Using the Hubble Space Telescope astronomers have spotted an important and extraordinary event in planetary evolution for the first time. The researchers have observed volcanic activity on a distant rocky planet reforming that world’s atmosphere.
The planet–GJ 1132 b–is believed by the team to have previously possessed an atmosphere that was stripped by the intense radiation emitted by the bright young red dwarf star it closely orbits. After its thick blanket of hydrogen and helium was expunged the planet was left as a rocky core roughly the size of Earth.
The astronomers believe that much of the hydrogen from GJ 1132 b’s initial atmosphere was absorbed by the exoplanet’s molten magma mantle creating a reservoir of the element which is now being slowly dispersed back into the atmosphere. This dispersal replenishes hydrogen being lost to space.
The fact that the planet’s volcanic activity is generating a secondary atmosphere that is replacing the first has come as a huge suprise to the researchers.
What makes this replacement atmosphere so interesting and useful to astronomers is the fact that has come from the planet’s interior. Thus its chemical composition–with abundant hydrogen, hydrogen cyanide, methane and ammonia with glimmers of a hydrocarbons–means that astronomers should be able to study the interior of the exoplanet by proxy.
“This second atmosphere comes from the surface and interior of the planet, and so it is a window onto the geology of another world,” explains Paul Rimmer, University of Cambridge, UK, who was part of the team that made the discovery. “A lot more work needs to be done to properly look through it, but the discovery of this window is of great importance.”
The finding could change the way we think about highly irradiated exoplanets which astronomers normally expect to lack atmospheres. “We first thought that these highly radiated planets would be pretty boring because we believed that they lost their atmospheres,” explains Raissa Estrela of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena, California, USA, another member of the research team. “But we looked at existing observations of this planet with Hubble and realised that there is an atmosphere there.”
Like Earth, But Really Different
Whilst sharing some similarities with Earth, GJ 1132 b is actually a very different world. GJ 1132 b has a similar density, size and age–around 4.5 billion years. Additionally, both planets started life as molten balls of rock with hydrogen-dominated atmospheres. But, whereas our planet was able to hang on to its atmosphere, the intense radiation GJ 1132 b was exposed to stripped that world’s gaseous envelope.
The differences become more extreme when considering the formation of both worlds. GJ 1132 b is the surviving core of a sub-Neptune exoplanet–a planet resembling Neptune but with a smaller mass–so didn’t start its life as a terrestrial world like we believe Earth did. Possibly the most extreme difference between the two worlds, however, is their relationships with their respective parent stars.
Whilst Earth orbits the Sun at a comfortable distance, rotating on its axis as it does so, GJ 1132 b orbits its red dwarf parent star in blisteringly close proximity. So-close that the exoplanet’s orbit period is just 36 hours. That isn’t the only major orbital difference, however. GJ 1132 b is tidally locked, meaning that the same face points towards its parent star throughout its orbit.
This isn’t the only source of heating the exoplanet is experiencing. The tidal force that the planet experiences due to its proximity to its parent star and that star’s gravitational force is permanently stretching and squeezing it.
This deformation is converted to heat beneath the planet’s surface, maintaining its mantle’s molten state. It could be this tidal heating that is driving the extreme volcanism and also causing the planet’s thin crust to crack, allowing hydron to escape and replenish the atmosphere.
The findings raise the question; how many of the terrestrial worlds we see are actually the stripped cores of sub-Neptunes?
“How many terrestrial planets don’t begin as terrestrials? Some may start as sub-Neptunes, and they become terrestrials through a mechanism whereby light evaporates the primordial atmosphere,” says Mark Swain of NASA’s Jet Propulsion Laboratory who led the research. “This process works early in a planet’s life when the star is hotter. Then the star cools down and the planet’s just sitting there.”
“So you’ve got this mechanism that can cook off the atmosphere in the first 100 million years, and then things settle down. And if you can regenerate the atmosphere, maybe you can keep it.”
The observations made by the team were part of the Hubble observing program and raise the interesting possibility that if this secondary atmosphere is thin enough, astronomers could actually see down to the surface of the exoplanet.
“This result is significant because it gives exoplanet scientists a way to figure out something about a planet’s geology from its atmosphere,” concludes Rimmer. “It is also important for understanding where the rocky planets in our own Solar System — Mercury, Venus, Earth and Mars, fit into the bigger picture of comparative planetology, in terms of the availability of hydrogen versus oxygen in the atmosphere.”
An international team of astronomers has discovered a nearby exoplanet orbiting a red dwarf star that is perfect for deeper investigation. In particular, this exoplanet could be a prime target for precise atmospheric measurements, something that, for planets outside the solar system, has so-far eluded astronomers.
The team’s findings documenting the discovery of this relatively close super-Earth–so-called because they have a mass greater than our planet but still lower than planets like Uranus and Neptune which are classified as ‘ice giants’–are published in the latest edition of the journal Science.
The team discovered Gliese 486 b whilst surveying 350 small red dwarf stars for signs of low-mass planets using the CARMENES spectrograph mounted on the 3.5m telescope at the Calar Alto Observatory telescope, Spain. The exoplanet was found due to the ‘wobble’ it caused in the orbit of its parent star.
“Our team is searching primarily for Earth-like and super-Earth planets orbiting nearby stars. In this case, we have found a nearby super-Earth, just 26 light-years away orbiting a small star every 1.5 or so Earth days,” Karen Collins, an astronomer at the Center for Astrophysics, Harvard & Smithsonian, and a co-author on the paper tells ZME Science. “We were certainly excited to have found a transit signal in the light curve of a star that is so close to the Sun in astronomical terms.
“We quickly realized that Gliese 486 b, with radial velocity mass measurements in hand, would likely become a prime target for additional detailed follow-up studies, particularly atmospheric investigations.”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
These investigations could include searching for the conditions necessary for life, or even for biomarkers left behind by simple lifeforms.
Colins continues by explaining that it is Gliese 486 b’s proximity–it is the third closest transiting exoplanet yet to be uncovered– that, amongst other things like its temperature, makes it a good candidate for more in-depth study. “Because Gliese 486 b is so close to the solar system, relative to most known transiting exoplanets, we may be able to probe the atmosphere of the planet using the upcoming James Webb Space Telescope and possibly other telescopes,” she explains.
That is, of course, if it actually has an atmosphere.
What We Know About Gliese 486 b So Far…
Whilst the team of astronomers may not yet be certain that Gliese 486 b has an atmosphere, there are some things that they do know about the exoplanet and its red dwarf home star.
“It is only about 30% larger than Earth but has a mass of about 2.8 times that of our planet,” study author Trifon Trifonov, Max Planck Institute for Astronomy, explains to ZME Science. The researcher adds that models suggest that the exoplanet’s composition is similar to Venus and Earth, including a metallic core. “Anyone standing on Gliese 486 b would feel a gravitational pull that is about 70% stronger than what we experience on Earth.”
In addition to being denser than the earth, Gliese 486 b is also much hotter according to Trifon. This is because the exoplanet revolves around its host star on a circular orbit every 1.47 days, with one side permanently pointing towards its parent star.
“The proximity to the red dwarf Gliese 486 heats the planet significantly, making its landscape hot and dry, interspersed with volcanos and glowing lava rivers,” Trifon says. “There are quite a few super-Earth type exoplanets already discovered. All of these exoplanets are exceptional on their own. In this context, the physical characteristics of Gliese 486 b are not uncommon. However, the proximity of Gliese 486 b, allowed us to measure its mass with unprecedented precision, thanks to observations done with the CARMENES and the MAROON-X instruments.”
From the information the astronomers do possess regarding Gliese 486 b, especially its mass, Collins adds that the clues it also has an appreciable atmosphere are in place.
“Because we do know that the planet surface gravity is relatively high–about 70% stronger than Earth–we believe that there is a chance the planet may have retained an appreciable atmosphere.”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
Using NASA’s Transiting Exoplanet Survey Satellite (TESS) spacecraft the astronomers were able to deduce that Gliese 486 b periodically crosses the stellar disk of its parent red dwarf star, a rare and fortuitous event.
“For transiting planets like Gliese 486 b, we have two primary methods to probe the atmospheres, if they exist,” Collins continues. “Transit spectroscopy allows us to study the planet’s atmosphere as the planet passes in front of the star from the telescope’s perspective.”
Collins says that should the exoplanet possess an atmosphere part of the light from its parent star that reaches our telescopes will have been filtered through this. This means that the light profile filtered by the atmosphere can be compared to an unfiltered version when the planet is not in front of the star.”By comparing the in-transit spectrum of the star with a spectrum of the star when the planet is not transiting, we can isolate atmospheric signals from the planet and possibly detect some of the components of the atmosphere.”
The second method detailed by Collins involves the detection of radiation directly from an exoplanet’s hot surface as it occupies different orbital phases across the star’s face. The emission spectrum that gives this technique its name–emission spectroscopy–reveals characteristic traits that indicate the presence of certain elements emitting and absorbing light in the exoplanet’s atmosphere.
“Its temperature of around 700 Kelvin makes it suitable for emission spectroscopy and phase curve studies in search of an atmosphere,” adds Trifonov.
The Golden Age of Exoplanet Science
Concluding our interview I ask Collins and Trionov if we are entering a ‘Golden Age’ for exoplanet science. They are both quick to correct me. “I would say we are living in it!” Trinov exclaims. “During the past three decades, astronomers have discovered thousands of exoplanets, and the number is increasing daily.
“Every day, we enhance our knowledge about the physical properties of exoplanets, their formation, and evolution.”
Trifon Trifonov, Max Planck Institute for Astronomy
Collins is equally assured that exoplanet science is in its prime, but adds that there is no decline in sight. “Frankly, I believe we have been in the golden age of exoplanet science for over a decade now,” the astronomer says. “Even so, with the advent of TESS to discover and measure the size of nearby small transiting planets, precise radial velocity machines like that of the CARMENES consortium and the MAROON-X instrument to measure their masses, and soon the James Webb Space Telescope to investigate their atmospheres, it’s fair to say that we are entering the golden age of well-characterized small planet exoplanet science.”
And Collins is clear how lucky she regards herself for just being involved with astronomy at this crucial juncture in its history. “I am excited to be involved in the search for and characterization of Earth-sized and Super-Earth planets such as Gliese 486 b,” says explains enthusiastically. “Precise atmospheric measurements are likely around the corner! What will this relatively new scientist from a small but progressive astrophysics program at a school in Kentucky be involved with next? Will we soon discover an Earth twin with an Earth-like atmosphere or even signs of life in an atmosphere?
“It is almost as if I’m living in a series of Star Trek. I can’t wait to see what we discover next!”
Karen Collins, Center for Astrophysics, Harvard & Smithsonian
Astronomers have discovered a unique system of exoplanets in which all but one of the planets orbit their parent star in a rare rhythm. The finding could force us to revise our ideas of how planets–including those in our own solar system–form.
The team–including astronomers from the University of Bern and the University of Geneva–used a combination of telescopes and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) to observe the star TOI-178, 200 light-years away from us in the constellation Sculptor.
Upon first glance, the astronomers believed that the star was orbited by just two exoplanets, both of which had the same orbits. Closer inspection revealed something surprising, however — six planets, five of which are locked in a rhythmic dance with each other.
“Through further observations, we realised that there were not two planets orbiting the star at roughly the same distance from it, but rather multiple planets in a very special configuration,” says lead researcher Adrien Leleu, University of Bern.
This rhythm reveals a star system that has remained undisturbed by cosmic events since its birth. But, even within this system exists a measure of chaos, with the compositions of the constituent planets displaying some disharmonious densities that are just as rare as their harmonious orbits.
The system consists of planets ranging from one to three times the size of Earth, with masses that range from 1.5 to 30 times that of our planet. Some are rocky and larger than Earth–so-called Super-Earths. Others are gaseous like the solar system’s outer bodies, but much smaller–a class of exoplanets called Mini Neptunes.
“This contrast between the rhythmic harmony of the orbital motion and the disorderly densities certainly challenges our understanding of the formation and evolution of planetary systems,” Leleu adds.
The team’s research is published in the journal Astronomy & Astrophysics.
Exoplanets in Resonance
All the exoplanets around TOI-178, barring the one closest to the star itself, are exhibiting a resonance can be observed in the repeated patterns in their orbits. These repeating orbits mean that the planets align at regular intervals as they loop their parent star.
A similar–albeit less complex– resonance can be found in our own solar system, not with planets, but with three of the moons of Jupiter. Io completes four full orbits for every orbit of Ganymede, whilst also completing two full orbits for every orbit of Europa. This is what is known as a 4:2:1 resonance.
TOI-178’s five outer planets possess a far more complex chain of resonance than these moons, however. The exoplanets exist in an 18:9:6:4:3 resonance. This means the first exoplanet in the chain–the second closest to the star overall–completes 18 orbits as the second in the chain completes nine, the third completes six, and the fourth completes 4, and the fifth (the sixth planet overall) completes three orbits.
The team were able to take the resonance of the four planets described above and use it to discover the fifth in the chain, which is the sixth and final planet overall.
The team believes that the exoplanet’s rhythmic orbits could teach them more the system than its current state, though. It could even provide them with a window into its past. “The orbits in this system are very well ordered, which tells us that this system has evolved quite gently since its birth,” explains co-author Yann Alibert from the University of Bern.
In fact, the resonance of the system shows that it has remained relatively undisturbed since its formation. Were it to have been significantly disturbed earlier in its life–by a giant impact or the gravitational influence of another system, for example– the fragile configuration of its orbits would have been obliterated.
Disharmony and Disorder Enter the Picture
It’s not all harmony within the TOI-178 exoplanets., however. Whilst their arrangements and neat and well-ordered, the densities and compositions of the individual exoplanets are much more disordered. It’s a disorder that is very different from what we observe in our solar system.
“It appears there is a planet as dense as the Earth right next to a very fluffy planet with half the density of Neptune, followed by a planet with the density of Neptune. It is not what we are used to,” team member Nathan Hara, University of Geneva, says, describing a system comprised of Super Earths and Mini Neptunes.
As is the case with most exoplanets, the planets in the TOI-178 system were difficult to spot. The team used data collected by the European Space Agency’s CHEOPS satellite, launched in December 2019, with instruments at the VLT located in Chile’s Atacama Desert region.
In addition to this data, the team used two of the most common techniques used by astronomers to spot exoplanets. Examing the light emitted by a parent star and how it dips indicates when a planet is transitting in front of it. Also, orbits of exoplanets around a parent star can cause it to ‘wobble’–something that can be seen in its light profile.
This combination of methods allowed the team to discover that the exoplanets in TOI-178 are orbiting their parent star far more rapidly and at a much closer distance than Earth orbits the Sun.
The innermost planet, the one not part of the resonant chain, is the fastest and orbits TOI-178 in just a matter of days. The slowest has an orbit that takes ten times this period to complete.
None of the planets seems to be orbiting in what is believed to be TOI-178’s habitable zone–the area in which water can exist as a liquid. But, the team believes that studying the resonance chain could uncover additional planets in this system, some with orbits that bring them within this region.–also colourfully nicknamed the ‘Goldilocks zone’ because it is neither too hot not too cold.
The researchers will continue to investigate this unique and extraordinary system and suggest that it could be a target for intense observation with the ESO’s Extremely Large Telescope (ELT) when it begins operations later this decade.
The ELT should be able to allow researchers to directly image the exoplanets in Goldilocks zones around stars like TOI-178 as well as study their atmospheres in detail.
This could reveal that the TOI-178 holds even more secrets than this study has revealled.
A. Leleu, Y. Alibert, N. C. Hara, et al, ‘Six transiting planets and a chain of Laplace resonances in TOI-178,’ Astronomy & Astrophysics, , (doi: 10.1051/0004-6361/202039767).
The star system of Trappist-1 is home to the largest group of Earth-like planets ever discovered elsewhere in the Universe by astronomers. This means that investigating these seven rocky worlds gives us a good idea of how common exoplanets with similar compositions to our own are in the Milky Way and the wider cosmos.
New research has revealed that these planets, which orbit the Trappist-1 star 40 light-years away from Earth, all have remarkably similar compositions and densities. Yet, all are less dense than Earth.
The results could indicate these are worlds with much more water than is found on earth, or possibly even that these planets are composed almost entirely of rust.
This similarity between the exoplanets makes the Trappist-1 system significantly different from our own solar system which consists of planets with radically compositions and densities. Trappist-1’s worlds are dense, meaning they are like the rocky planets in our solar system, Earth, Mars, Venus, and Mercury. The system seems to be lacking larger gas dominated planets like Jupiter, Saturn, Uranus and Neptune.
The finding, documented in a paper published in the Planetary science Journal shows how the system, first discovered in 2016, offers insight into the wide variety of planetary systems that could fill the Universe.
“The new observations allowed us to use transit data from a much longer time span than was available to us for the 2018 calculations,” explains Simon Grimm of the University of Bern, who as well as being involved in the current study, was part of a 2018 team that provided the most accurate calculation of the masses of the seven planets thus far. “With the new data, we were able to refine the mass and density determinations of all seven planets.
“It turned out that the derived densities of the planets are even more similar than we had previously expected.”
Seven Exoplanets with Similar Densities
The similarity in densities observed in the Trappist-1 exoplanets seen by the astronomers hailing from the Universities of Bern, Geneva and Zurich, indicates that there is a good chance they are composed of the same materials at similar ratios.
These are the same materials that we believe form most terrestrial planets, iron, oxygen, magnesium, and silicon. But there is a significant difference between our terrestrial world and the Trappist-1 exoplanets.
The planets in the Trappist-1 system appear to be about 8% less dense than the Earth. This suggests that the materials that comprise them exist in different ratios than they do throughout our home planet.
This difference in density could be the result of several different factors.
One of the possibilities being investigated by the team is that the surfaces of the Trappist-1 exoplanets could be covered with water, reducing their overall density. Combining the planetary interior models with the planetary atmosphere models, the team was able to evaluate the water content of the seven TRAPPIST-1 planets with what Martin Turbet, an astrophysicist at the University of Geneva and co-author of the study describes as “a precision literally unprecedented for this category of planets.”
For the Trappist-1 system’s four outermost planets, should water account for the difference in density, the team has estimated that water would account for 5% of their overall masses. This is considerably more than the 0.1% of Earth’s total mass made up of water.
Rust Nevers Sleeps for the Trappist-1 Planets
Another possibility that could explain why the Trappist-1 exoplanets have lower densities than Earth is the fact that they could be composed of less iron than our planet is–21% rather than the 32% found in the Earth.
It’s also possible that the iron within the seven exoplanets could be bonded with oxygen forming iron oxides–commonly known as rust. This additional oxygen would reduce the planet’s densities.
Iron oxides give Mars its rust-red colour, but they are pretty much confined to its surface. Its core is comprised of non-oxidized iron like the solar system’s other terrestrial planets. If iron-oxide accounts for the seven exoplanet’s lower densities it implies that these worlds are rusty throughout and lacking solid non-oxidized iron cores.
“The lower density might be caused by a combination of the two scenarios – less iron overall than and some oxidized iron,” explains Eric Angol, an astrophysicist at the University of Washington and lead author of the new study. “They might contain less iron than Earth and some oxidized iron like Mars.”
Angol also points out that the Trappist-1 planets are likely to have a low-water content, an idea supported by previous research. “Our internal and atmospheric structure models show that the three inner planets of the TRAPPIST-1 system are likely to be waterless and that the four outer planets have no more than a few per cent water, possibly in liquid form, on their surfaces,” says Turbet.
This seems to favour the theory that the lower density of the Trappist-1 planets is a result of one or both of the iron scenarios suggested by the researchers.
There’s Still a Lot to Learn from Trappist-1
Since its discovery in 2o16, the Trappist system has been the subject of a wealth of observations made by both space and ground-based telescopes alike. Before it was decommissioned at the start of January 2020 the team used the Spitzer Space Telescope to collect their data. This telescope, operated by NASA’s Jet Propulsion Laboratory, alone has clocked in more than 1,000 hours of targeted observations of the exoplanets.
This new study demonstrated the importance of studying systems such as Trappist-1 for extended periods of time.
Caroline Dorn, an astrophysicist at the University of Zurich also highlights the fact that studying systems like this could answer questions about the habitability of exoplanets and the possibility of life elsewhere in the Universe.
“The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system,” concludes Dorn. “And we can actually learn more about an individual planet by studying its neighbours as well, so this system is perfect for that.”
“The night sky is full of planets, and it’s only been within the last 30 years that we’ve been able to start unravelling their mysteries, also for determining the habitability of these planets.”
Agol. E., Dorn. C., Grimm. S. L., et al, ‘Refining the transit timing and photometric analysis of TRAPPIST-1: Masses, radii, densities, dynamics, and ephemerides,’ Planetary Science Journal, [https://arxiv.org/abs/2010.01074]
A team of researchers from the University of Bern has discovered a very different binary system 450 light-years from Earth. The system — CFHTWIR-Oph 98 or Oph 98 for short — has twin occupants that appeared at first sight to be exoplanets existing in a star-less system. A deeper examination has revealed that they are brown dwarfs — Oph 98 A and Oph 98 B respectively — astronomical objects that are similar to stars but smaller and cooler.
These brown dwarfs wander the galaxy together, orbiting each other at an incredibly large distance equivalent to 200 times the distance between Earth and the Sun.
The discovery of the curious Oph 98 system by the research team led by Clémence Fontanive from the Center for Space and Habitability (CSH) and National Centre of Competence in Research PlanetS (NCCR PlanetS) is documented in a paper published in The Astrophysical Journal Letters.
A Star that Failed
The Oph 98 is a relativity new-born system in astrophysical terms, forming just 3 million years ago in the Ophiuchus stellar nursery (hence the ‘Oph’ element of its name). Its relative youth has some interesting consequences for the bodies that comprise it and led the team to properly identify its constituent bodies.
The system has not existed for long enough for it to start forming planets. This means that Oph 98 A and B must have both formed via the same mechanisms that give rise to stars. This conclusion is also supported by the fact that Oph 98 B is roughly the right size to be a planet, but Oph A is too small to have the reservoir of material needed to form a planet so large. That means they must be brown dwarfs.
“This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scaled-down versions all the way down to these planetary masses,” says Fontanive.
The fact that brown dwarfs form in ways that are similar to stars and share similar masses, but do not ignite with the nuclear processes that power stars, has often led to them being nicknamed ‘failed stars.’ It is extremely rare for star-forming processes to create worlds that go on to exist in a system such as this.
The objects are rare examples of astronomical bodies similar to giant exoplanets that orbit each other without a parent star. Both are young brown dwarfs, with Oph 98 A being the larger of the two with a mass 15 times that of Jupiter. Its smaller companion — Oph 98 B — has a mass equivalent to 8 times that of the gas giant, which is the largest body other than the Sun in our solar system.
This isn’t the only thing that makes Oph 98 unique, however.
Brown Dwarfs with a Weak Bond
Another thing that makes the Oph 98 system so remarkable is the fact that, like all binary systems, the bodies are gravitationally bound. These bonds are greater with objects of greater mass but follow an inverse square law — meaning the bond’s strength falls off quickly as separation distances increase. Because these objects have relatively small mass coupled with an extremely large separation, the gravitational bond between them is one of the weakest in terms of energy that astronomers have ever observed.
Observing this system at all is no mean feat as brown dwarfs — especially low-mass ones — emit very little electromagnetic radiation and are thus, not easy to spot.
“Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation,” explains Fontanive. “This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light.”
This visibility challenge was further compounded by the fact that Oph 98 and the Ophiuchus galaxy cluster itself is embedded in a dense cloud of dust that scatters visible light. “Infrared observations are the only way to see through this dust,” the researcher adds.
In fact, the team’s discovery was only made possible by the impressive power of the Hubble Space Telescope and the fact that it makes its observations from above Earth.
Hubble Shines Through Again
The Hubble Space Telescope is one of the only telescopes capable of observing objects as faint as the Oph 98 A and B and resolving the image of the brown dwarfs at such tight angles.
“Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky,” Fontanive continues.
Hubble’s space-based vantage point is also crucial for the observation of such objects. This is because the infrared signatures that are used to observe brown dwarfs arise from water vapors that form in their upper atmospheres. As Earth’s atmosphere is full of water also producing this signal, the fainter trace from distant brown dwarfs is almost always obscured beyond detection for telescopes at the planet’s surface.
“Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source we saw next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky,” says Fontanive.
Interestingly, the team’s findings have helped confirm the fact that the Oph 98 system has actually been spotted before. The binary was also visible in data collected by the Canada-France-Hawaii Telescope (CFHT), located atop the summit of Mauna Kea, Hawaii, 14 years ago. This older data helped the team confirm how Oph 98 A and B move together across the galaxy as a pair.
“We observed the system again this summer from another Hawaiian observatory, the United Kingdom Infra-Red Telescope. Using these data, we were able to confirm that Oph 98 A and B are moving together across the sky over time, relative to other stars located behind them, which is evidence that they are bound to each other in a binary pair”, explains Fontanive. “We are really witnessing an incredibly rare output of stellar formation processes.”
Fontanive. C., et al, ‘A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus,’ The Astrophysical Journal Letters, , [https://arxiv.org/abs/2011.08871]
Researchers believe that our galaxy is teeming with cosmic orphans, planets wandering free of a parent star. Though common, these rogue planets are difficult to spot, especially when they are in the size range of the earth.
Despite this difficulty; an international team of astronomers including Przemek Mróz, a postdoctoral scholar at the California Institute of Technology (Caltech) and Radosław Poleski from the Astronomical Observatory of the University of Warsaw, have spotted what they believe to be a free-floating planet with a size and mass somewhere in the range of Mars and Earth, wandering the Milky Way.
The discovery represents a major step forward in the field of exoplanet investigation as it is the first earth-sized ‘rogue planet’ ever observed.
“We found a planet that seems extremely lonely and small, far away in the Universe,” Poleski tells ZME Science. “If you can imagine, Earth is in a sandbox surrounded by lots of other planets, and light from the Sun. This planet isn’t. It’s truly alone.”
The rogue planet the team found — OGLE-2016-BLG-1928 — is believed to be the smallest free-floating planet ever discovered. It was found in data collected by Optical Gravitational Lensing Experiment (OGLE), a Polish astronomical project based at the University of Warsaw. Previously discovered rogues — such as the first-ever recorded free-floating planet also found by OGLE in 2016 — are closer in size to Jupiter.
“We discovered the smallest free-floating planet candidate to date. The planet is likely smaller than Earth, which is consistent with the predictions of planet-formation theories,” Mróz — lead author of the team’s study published in Astrophysical Journal Letters — explains to ZME Science. “Free-floating planets are too faint to be observed directly — we can detect them using gravitational microlensing via their light-bending gravity.”
The Gravity of the Situation
The team spotted this wandering planet using the technique of gravitational microlensing, often utilised to spot exoplanets — planets outside our solar system. Exoplanets can’t often be observed directly, and when they can it’s a result of interaction with radiation from their parent star — for example, the dimming effect exoplanets have when they cross in front of their star and block some of the light it emits. Clearly, as rogue planets don’t have a parent star, they don’t have these interactions, making micro-lensing events the only way of spotting them.
“Microlensing occurs when a lensing object — a free-floating planet or star — passes between an Earth-based observer and a distant source star, its gravity may deflect and focus light from the source,” Mróz explains to ZME Science. “The observer will measure a short brightening of the source star, which we call a gravitational microlensing event.”
Mróz continues by explaining that the duration of microlensing events depends on the mass of the object acting as a gravitational lens. “The less massive the lens, the shorter the microlensing event. Most of the observed events, which typically last several days, are caused by stars,” Mróz says. “Microlensing events attributed to free-floating planets usually last barely a few hours which makes them difficult to spot. We need to very frequently observe the same part of the sky to spot brief brightenings caused by free-floating planets.”
By measuring the duration of a microlensing event and shape of its light curve astronomers can estimate the mass of the lensing object. That is how the team were able to ascertain this free-floating planet is approximately Earth-sized. “Hence, we can discover very dim objects, like black holes, or free-floating planets,” says Poleski. “We found it an event, which has a timescale of 41 minutes. And it’s the shortest event ever discovered.”
Poleski explains that the lack of any other lensing body in the system told the team that it is a very strong candidate for a free-floating planet. He adds: “We know it’s a planet because of the very short timescale and we think it’s free-floating because we don’t see any star next to it.”
Going Rogue. How Free-Floating Planets Come to Wander the Universe Alone
Astronomers believe that free-floating planets actually formed in protoplanetary disks around stars in the same way that ‘ordinary’ planets are. At some point, they are ejected from their parent planetary systems, probably after gravitational interactions with other bodies, for example, with other planets in the system.
“Some low-mass planets are expected to be ejected from their parent planetary systems during the early stages of planetary system formation,” says Mróz. “According to planet formation theories, most of the ejected planets should be smaller than Earth. Theories of planet formation predict that typical masses of ejected planets should be between 0.3 and 1.0 Earth masses. Thus, the properties of this event fit the theoretical expectations.”
These free-floating rogue planets are believed to be fairly common, but researchers can’t be certain because they are so difficult to spot. “Our current studies indicate that the frequency of low-mass–in the Earth to super-Earth-mass range–free-floating or wide-orbit planets is similar to that of stars — there are about two-five such objects per each star in the Milky Way,” says Mróz. “These numbers are very uncertain because they are based on a few sightings of short-timescale microlensing events. However, if free-floating/wide-orbit planets were less frequent than stars, we would have observed much fewer short-timescale events than we do.”
The researcher adds that though these objects are relatively common, the chances of observing microlensing events caused by them are still extremely small. “Three objects — source, lens, and observer — must be nearly perfectly aligned,” Mróz says. “If we observed only one source star, we would have to wait almost a million year to see the source being microlensed.”
In fact, one of the extraordinary elements of the team’s study is that such a short duration lensing event wasn’t believed to be observable given the sensitivity of the current generation of telescopes.
“The surprise, in general, was that with current technology we could define such a short time event,” Poleski says. “It’s especially surprising if you beat the previous record by a factor of few.”
The Nancy Grace Roman Telescope and Future Rogue Reconnaissance
For Mróz, there are still questions that he would like to see answered about OGLE-2016-BLG-1928. Primarily, confirming that it definitely is a free-floating planet.
“We aren’t fully sure whether our planet is free-floating or not. Our observations rule out the presence of stellar companions within 10 astronomical units–930 million miles–of the planet, but the planet may have a more distant companion,” Mróz says. “Let’s imagine that we’re observing microlensing events by a doppelganger of the Solar System. If Jupiter or Saturn caused a microlensing event, we would see a signature of the Sun in the microlensing event light curve. However, microlensing events by Uranus or Neptune would likely look like those of free-floating planets, because they are very far from the Sun.”
Fortunately, Mróz says that should be possible to distinguish between free-floating and wide-orbit planets. “The lens is moving relative to the source star in the sky and — a few years after the microlensing event — the lens and source should separate in the sky,” the researcher elaborates. “If the lens has a stellar companion, we will see some excess of light at its position. If it is a free-floating planet, we will not.”
Whilst this method may seem simple, Mróz says we cannot apply it now, because the existing telescopes are not powerful enough. This includes the instrument that conducted the long-term observations that gave rise to the OGLE sky survey–the data from which the team found the micro-lensing event OGLE-2016-BLG-1928.
“[The discovery of OGLE-2016-BLG-1928] was part of the larger search for microlensing events in general, which we perform in a number of steps,” Poleski tells ZME. “In one step, I started looking at the wide orbit planets — planets similar to Uranus, or Neptune and on similar orbits. And while looking for those, I screened a list of candidate microlensing events in general and I found this one.”
Soon NASA’s Nancy Grace Roman Telescope will take over the search for microlensing events, but in the meantime, there is still data from OGLE and other projects to be examined. “We now have more data and other surveys are also collecting data. So we hope to analyze those,” Poleski says. “The longer-term future is the launch of the Nancy Grace Roman Space Telescope. It will be a telescope similar to the Hubble telescope, only with new infrared and infrared cameras and that camera field of view larger than the Hubble Space Telescope.
“One of the main projects for the Raman telescope will be to observe galactic bulge in search for microlensing planets, including free-floating planets.”
Mroz, P., Poleski, R., Gould, A. et al., ‘A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event,’ Astrophysical Journal Letters,  DOI: 10.3847/2041–8213/abbfad
Astronomers have discovered a spectacular first in terms of star clusters and planet-forming discs of gas, a system–GW Orionis–with a warped disc with torn out inner rings. The team believes that the disc’s odd shape –which defies the common view of a flat plane orbiting planets and gas discs–was created when the misalignment of the three stars at the centre of the disc caused it to fracture into distinct rings.
As well as being extraordinary in its own right, the astronomers believe that the warped disc could harbour exotic and strange exoplanets– not unlike Tatooine in Star Wars series– which formed within the inclined rings and are, for now, hidden from view.
“The idea that planets form in neatly-arranged, flat discs around young stars goes back to the 18th century and Kant and Laplace,” research team-leader Stefan Kraus, a professor of astrophysics at the University of Exeter in the UK, tells ZME Science. “Our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disc.”
“‘Tatooine’ planets that orbit around 2 or 3 suns have already been envisioned by science fiction and some Tatooine exoplanets have already been found. Here, we observe how such planets form and find that they can form on extreme, highly inclined orbits — in configurations that are completely different from the ‘neat’ arrangement observed in the Solar System.”
Stefan Kraus, professor of astrophysics, the University of Exeter
GW Orionis is Twisted
The team saw the warped shape of the system GW Orionis, which sits 1300 light-years from Earth in the constellation of Orion, in observations made by the Very Large Telescope (VLT) operated by European Southern Observatory (ESO), and the Atacama Large Millimeter/ submillimeter Array (ALMA) based in the Chilean desert. But, properly envisioning this shape and its cause meant studying the system for a staggering 11 years.
“The most important result from our study is that we can identify the cause for the misalignments and link it to the ’disc tearing’ effect that has been proposed by theorists 8 years ago, but has not been observed so far,” Kraus continues. “For this, it was essential to measure the orbital motion of the three stars that are in the centre of the system over their full 11-year orbital period.
“We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc.”
Stefan Kraus, professor of astrophysics, the University of Exeter
“We have observed GW Orionis, a triple star system surrounded by a planet-forming disc, with several different telescopes including the VLT and ALMA. After observing the three stars for several years, our team was able to calculate the orbits very accurately,” team member Alison Young of the Universities of Exeter and Leicester tells ZME Science. “This data allowed us to build a detailed computer model of the system, which predicted that the disc would be bent and even torn to form a separate inner ring.”
“A couple of years later when we received the data back from the VLT and ALMA, the image of a disc bent and even torn to form a separate inner ring, were stunning.”
Alison Young of the Universities of Exeter and Leicester
A paper detailing their work is published in the journal Science.
That Tears It! How GW Orionis got warped
The images of GW Orionis that the astronomers collected represent the first visualisation of disc-tearing ever captured by researchers. This tearing and the ‘warped’ effect it created marks this out as a planetary system exceptionally different from the solar system.
“The radial shadows in the VLT SPHERE image are clear evidence that the ring is tilted. To form a narrow shadow like this on the disc you need a fairly opaque ring of material that is at an angle to the disc surface blocking the starlight,” Young explains. “This result is consistent with some modelling done by members of the team which worked out the most likely orientations of the components of the system.”
“This system is unusual because the orbits of the three stars are misaligned, unlike the planets in the solar system they do not orbit in the same plane, and these stars host a large disc that is also tilted relative to their orbits,” Young continues. “We see all sorts of intriguing structures now in images of protoplanetary discs but this is the first direct evidence of the disc tearing effect.”
The observations also gave the researchers an idea of the vast scale of the GW Orionis disc.
“The ring harbours about 30 Earth masses of dust, which is likely sufficient for planet formation to occur in the ring. Any planets formed within the misaligned ring will orbit the star on highly oblique orbits and we predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging surveys.”
Stefan Kraus, professor of astrophysics, the University of Exeter
As well as being able to reconstruct the torn disc of GW Orionis from the ALMA data in conjunction with data collected from several other telescopes, the team has been able to piece together the process by which this tearing likely occurred. They conclude that it could be a result of those three, misaligned stars. Something that initially came as a surprise to the astronomers.
“One very intriguing aspect of GW Orionis is that the orbits of the stars are strongly misaligned with respect to each other, and they are also strongly titled with respect to the large-scale disc. This wasn’t clear at the time when we started the study and became only apparent after monitoring the orbit motion for the full 11-years orbital period.”
Stefan Kraus, professor of astrophysics, the University of Exeter
Alison Young explains that because the disc surrounds three stars and the orbits of those stars are misaligned with respect to each other, the gravitational pull on the disc is not the same all the way around. This means that the gas and dust orbiting in the disc around all three stars feels a different force at different positions in the disc. This is what tears the disc apart into separate rings.
“Our study shows that the strong distortions observed in the disc– such as the warp and torn-away ring–can be explained by the conflicting gravitational pull from the 3 stars. The key aspect is that the orbits are strongly misaligned with the disc.
Stefan Kraus, professor of astrophysics, the University of Exeter
How Warped Rings and Multiple Suns Effect Exoplanets
One interesting consequence of the warping of this gas and dust is that fact that it will wrap rings of material around any planets forming within it. This tearing also has a marked effect on these exoplanets’ orbits. This leads to conditions that would make the exoplanets in the GW Orionis system significantly different from planets in our own solar system.
“The planets in our solar system all have more-or-less aligned orbits. Any planets that form in the warped disc or misaligned ring could have highly inclined orbits,” says Young. “Further out, the disc is flatter and any planets that form there are likely to orbit in a similar plane to the disc. Of course, any planets that form in the GW Orionis system will also have three suns!”
Kraus points out that planets with oblique orbits have been identified before–particularly in the case of ‘Hot Jupiters’–planets with a mass and size comparable to the solar system’s largest planet, but that orbit closer to their star and transit across its face.
“Hot Jupiters orbit their stars very close in, and it is clear that they have not formed on the oblique orbits were we observe them. Instead, they must have been moved onto these orbits through migration processes,” Kraus says. “We haven’t found yet any long-period planets on oblique orbits–comparable to Earth or Jupiter. However, our research shows that such planets could form in the torn-apart rings around multiple systems.
“Given that about half of all stars are found in multiple systems, there could be a huge population of such long-period planets with high obliquity.”
Stefan Kraus, professor of astrophysics, the University of Exeter
Existing under the glare of three suns would make the planets in the GW Orionis system similar in some ways to an exoplanet discovered by astronomers from the University of Arizona in 2016.
The young exoplanet HD 131399Ab, 340 light-years from Earth in the constellation Centaurus, has a scorching hot temperature of around 580 C and exists in a state of constant daytime. It too has been compared to the planet of Tatooine from the Star Wars series. But Straus believes the planets in GW Orionis could be much cooler than this–or could alternate between cool and hot climates.
“Planets on such orbits could have stable atmospheric conditions, but would be ‘ice worlds’ with low temperatures on their surfaces,” Kraus says. “Planets that might have formed in the circumstellar/ circumbinary disc would experience extreme temperature variations, depending on where they are on their orbit. This should result in a strongly variable climate.”
Further Questions and Future Investigations: Delving Deeper into GW Orionis
Questions still remain about the GW Orionis system especially in light of research from another team who investigated the system with the ALMA telescope. This work-published in The Astrophysical Journal Letters earlier this year– suggests that our understanding of how the disc became warped is missing a vital component. “We think that the presence of a planet between these rings is needed to explain why the disc tore apart,” says Jiaqing Bi of the University of Victoria, Canada, lead author of a paper.
Speaking to ZME Science exclusively, Kraus addresses this earlier research: “This alternative scenario, where a yet-unseen planet located between the inner and middle ring might be the cause for the unusual disc shape, is more speculative, as such as planet has not been found yet,” the astrophysicist says. “Also, the paper’s authors had less information on the 3-dimensional shape of the disk as their ALMA observations had 6x lower solution and they did not have scattered-light images showing the shadows. Plus, they did not know the full orbits.”
Young continues by adding one future question regarding GW Orionis she would like to see answered also concerns the mechanism that caused the warping of the as and dust planet-forming disc.
“An important question we need to look at is how these systems came to be misaligned in the first place. Was the disc formed with the stars, did the material forming the disc arrive later, or did the system get disrupted at some point?”
Alison Young of the Universities of Exeter and Leicester
“Think of a star as a spinning top tilted at an angle,” the researcher suggests. “We want to find out how tilted the stars are so we can check whether a star’s tilt–or ‘spin axis’– matches the tilt of its disc, or if the stars in a binary or triple system have the same or different tilts.”
Some members of the team that made this discovery are currently developing a technique for measuring the spin axis of stars which could massively aid the understanding of how these systems formed.
Remembering that whilst this is not the first system discovered with such a warped disc, it is the first with a directly observed torn disc. This means the key to answering lingering questions likely lies in the direct observation of more systems that share features with GW Orionis.
“There are a few planet-forming discs that show some evidence of warping but for these, it is unclear what is causing the effect or there is an alternative scenario that can explain the observations, that has not been ruled out yet,” adds Young. “This is the first time that disc tearing has been directly observed and the only system so far for which we can link the structure with the physical mechanism behind it.”
Young suggests that the results of a larger survey performed by the ALMA array could provide clearer information about the motion of gas in planet-forming discs and their chemical composition, thus helping the team gather more information about the GW Orionis disc.
“We would like to obtain high-resolution observations of molecular emission from GW Orionis to shed more light on the motion of the gas in the disc and perhaps reveal any planets that are forming,” she explains. “Of course, we also are keen to understand if there are differences in how planets might form in warped discs compared to flat discs around a single star and we will be working on new computer models to look at this, using what we have learned from our observations.”
Young explains the importance of the GW Orionis images the team captured, whilst focusing on one image that for her, brought home the significance of the investigation in which she played a part.
“I find the SPHERE image [above left] in particular amazing because we can really see the disc is a 3-dimensional structure with a surface covered in bumps and shadows. We are looking at what could eventually become an unusual type of planetary system in the very process of forming.”
Alison Young of the Universities of Exeter and Leicester
For Stefan Kraus, the beauty of investigating a system such as GW Orionis is the wonder to imagining what it is like to stand on the surface of such a world and stare up into sky. Kraus concludes: “Half of the sky would be covered by a massive disc warp that is being illuminated by the 3 stars, intercepted by narrow shadows that are cast by the misaligned disc ring.”
“I find it fascinating to imagine how the sky would look like from any planet in such a system — one would see not only the 3 stars dancing around each other at different speeds but also a massive dust ring extending over the whole firmament.”
Stefan Kraus, professor of astrophysics, the University of Exeter
Our galaxy is teeming with rogue planets either torn from their parent stars by chaotic conditions or born separate from a star. These orphan planets could be discovered en masse by an outcoming NASA project — Nancy Grace Roman Space Telescope.
The Milky Way is home to a multitude of lonely drifting objects, galactic orphans — with a mass similar to that of a planet — separated from a parent star. These nomad planets freely drift through galaxies alone, thus challenging the commonly accepted image of planets orbiting a parent star. ‘Rogue planets’ could, in fact, outnumber stars in our galaxy, a new study published in the Astronomical Journal indicates.
“Think about how crazy it is that there could be an Earth, a Mars, or a Jupiter floating all alone through the galaxy. You would have a perfect view of the night sky but stuck in an eternal night,” lead author of the study, Samson Johnson, an astronomy graduate student at The Ohio State University, tells ZME Science. “Although these planets could not host life, it is quite a place to travel to with your imagination. The possibility of rogue planets in our galaxy had not occurred to me until coming to Ohio State.”
Up to now, very few very of these orphan planets have actually been spotted by astronomers, but the authors’ simulations suggest that with the upcoming launch of NASA’s Nancy Grace Roman Space Telescope in the mid-2020s, this situation could change. Maybe, drastically so.
“We performed simulations of the upcoming Nancy Grace Roman Space Telescope (Roman) Galactic Exoplanet Survey to determine how sensitive it is to microlensing events caused by rogue planets,” Johnson says. “Roman will be good at detecting microlensing events from any type of ‘lens’ — whether it be a star or something else — because it has a large field of view and a high observational cadence.”
The team’s simulations showed that Roman could spot hundreds of these mysterious rogue planets, in the process, helping researchers identify how they came to wander the galaxy alone and indicating how great this population could be in the wider Universe.
Rogue by Name, Rogue by Nature: Mysterious and Missing
Thus far, much mystery surrounds the process that sees these planets freed from orbit around a star. The main two competing theories suggest that these stars either are thrown free of their parent star, or form in isolation. Each process would likely lead to rogue planets with radically different qualities.
“The first idea suggests that rogue planets form like planets in the Solar System, condensing from the protoplanetary disk that accompanies stars when they are born,” Johnson explains. “But as the evolution of planetary systems can be chaotic and messy, members can be ejected from the system leading to most likely rogue planets with masses similar to Mars or Earth.”
Johnson goes on to offer an alternative method of rogue planet formation that would see them form in isolation, similar to stars that form from giant collapsing gas clouds. “This formation process would likely produce objects with masses similar to Jupiter, roughly a few hundred times that of the Earth.”
“This likely can’t produce very low-mass planets — similar to the mass of the Earth. These almost certainly formed via the former process,” adds co-author Scott Gaudi, a professor of astronomy and distinguished university scholar at Ohio State. “The universe could be teeming with rogue planets and we wouldn’t even know it.”
The question is if these objects are so common, why have we spotted so few of them? “The difficulty with detecting rogue planets is that they emit essentially no light,” Gaudi explains. “Since detecting light from an object is the main tool astronomers use to find objects, rogue planets have been elusive.”
Astronomers can use a method called gravitational microlensing to spot rogue planets, but this method isn’t without its challenges, as Gaudi elucidates:
“Microlensing events are both unpredictable and exceedingly rare, and so one must monitor hundreds of millions of stars nearly continuously to detect these events,” the researcher tells ZME Science. “This requires looking at very dense stellar fields, such as those near the centre of our galaxy. It also requires a relatively large field of view.”
Additionally, as the centre of the Milky Way is highly obscured by requiring us to look at it in the near-infrared region of the electromagnetic spectrum — a task that is extremely difficult as the Earth’s atmosphere makes the sky extremely bright in near-infrared light.
“All of these points argue for a space-based, high angular resolution, wide-field, near-infrared telescope,” says Gaudi. “That’s where Roman — formally the Wide Field InfraRed Survey Telescope (WFIRST) — comes in.”
Nancy Grace Roman Space Telescope (and Einstein) to the Rescue!
The Roman telescope — named after Nancy Grace Roman, NASA’s first chief astronomer, who paved the way for space telescopes focused on the broader universe–will launch in the mid-2020s. It is set to become the first telescope that will attempt a census of rogue planets — focusing on planets in the Milky Way, between our sun and the centre of our galaxy, thus, covering some 24,000 light-years.
The team’s study consisted of simulations created to discover just how sensitive the Roman telescope could be to the microlensing events that indicate the presence of rogue planets, finding in the process, that the next generation space telescope was 10 times as sensitive as current Earth-based telescopes. This difference in sensitivity came as a surprise to the researchers themselves. “Determining just how sensitive Roman is was a real shock,” Johnson says. “It might even be able to tell us about moons that are ejected from planetary systems! We also, found a new ‘microlensing degeneracy’ in the process of the study — the subject another paper that will be coming out shortly.”
Johnson’s co-author Gaudi echoes this surprise. “I was surprised that Roman was sensitive to rogue planets with mass as low as that of Mars and that the signals were so strong,” the researcher adds. “I did not expect that before we started the simulations.”
The phenomenon that Roman will exploit to make its observations stems from a prediction made in Einstein’s theory of general relativity, that suggests that objects with mass ‘warp’ the fabric of space around them. The most common analogy used to explain this phenomenon is ‘dents’ created in a stretched rubber sheet by placing objects of varying mass upon it. The heavier the object — thus the greater the mass — the larger the dent.
This warping of space isn’t just responsible for the orbits of planets, it also curves the paths of light rays, the straight paths curving as they pass the ‘dents’ in space. This means that light from a background source is bent by the effect of the mass of a foreground object. The effect has recently been used to spot a distant Milky Way ‘look alike’. But in that case, and in the case of many gravitational lensing events, the intervening object was a galaxy, not a rogue planet, and thus was a much less subtle, more long-lasting, and thus less hard to detect effect than ‘microlensing’ caused by a rogue planet.
“Essentially, a microlensing event happens when a foreground object — in this case, a rogue planet — comes into very close alignment with a background star. The gravity of the foreground object focuses light from the background star, causing it to be magnified,” Gaudi says. “The magnification increases as the foreground object comes into alignment with the background star, and then decreases as the foreground object moves away from the background star.”
As Johnson points out, microlensing is an important and exciting way to study exoplanets — planets outside the solar system — but when coupled with Roman, it becomes key to spotting planetary orphans.
“Roman really is our best bet to find these objects. The next best thing would be Roman 2.0 — with a larger field of view and higher cadence,” the researcher tells ZME, stating that rogue planets are just part of the bigger picture that this forthcoming space-based telescope could allow us to see. “I’m hoping to do as much work with Roman as possible. The next big project is determining what Roman will be able to teach us about the frequency of Earth-analogs — Earth-mass planets in the habitable zones of Sun-like stars.”
Johnson. S. A., Penny. M, Gaudi. B. S, et al, ‘Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free-floating Planet Detection Rates*,’ The Astronomical Journal, .
Europe’s newest space telescope, CHEOPS, has completed its testing period and is ready to help us peer into distant worlds.
CHEOPS, or the CHaracterising ExOPlanet Satellite is the European Space Agency’s (ESA) newest tool in the sky. It was launched in December with the aim of studying exoplanets, with early targets including the so-called “Styrofoam world” Kelt-11b; the “lava planet” 55 Cancri-e; and the “evaporating planet” GJ-436b.
“We have a very stable satellite; the pointing is excellent — better than requirements. And this is going to be a real benefit to the mission,” said Dr Kate Isaak, lead scientist of the project behind CHEOPS at ESA for BBC News. “From the spacecraft side, from the instrument side, from the analysis of the data that we’re getting — we can see that this mission has huge promise.”
CHEOPS will take a closer look at points of interest identified in previous surveys of the sky, in the hope of improving our understanding of what these objects actually are. While the coronavirus crisis has meant considerable disruption for many space projects, CHEOPS has been largely unaffected.
The satellite is a joint project between the Swiss Space Office and ESA. It is “a small photometric observatory” that will observe and measure the transits of exoplanets as they pass in front of their stars — allowing us to better estimate their size. Combined with data about their mass obtained from other devices, such measurements would allow researchers to estimate the planets’ densities and from that, their chemical composition and internal structure.
Prof David Ehrenreich from the University of Geneva, which participated in the project, said a few early observations made with CHEOPS would be of “super-Earths” such as 55 Cancri-e. This planet is eight times as massive as Earth but has 18-hour-long days. Due to its size and proximity to its star, researchers suspect that 55 Cancri-e harbors an ocean — an ocean of molten, liquid rock.
“These are planets that are assumed to be rocky like Earth – but much bigger, more massive. And much hotter, too. Lava worlds,” he explained.
Roughly 80% of observing time on CHEOPS has been earmarked for participants in the project, including the ESA, universities in Bern and Geneva, and other members in eleven European nations. The remaining 20% is being offered to the community at large, with proposals to be reviewed in the coming days.
“We have built a whole theory of planet formation by observing only the eight planets of our Solar System, but by extending our observations to other kinds of planets that have no counterpart in our Solar System,” Prof. Didier Queloz told the BBC — a professor from the universities of Cambridge and Geneva, and a Nobel Prize Laureate.
“We should be able to add the missing parts of this theory and get, let’s say, a bigger perspective on how we actually fit in.”
Science planning for CHEOPS is run from Geneva; the telescope itself is controlled from Spain, at the National Institute for Aerospace Technology in Torrejon on the outskirts of Madrid.
We have all, at some point, stared at the stars and dreamed lazily of other worlds, but, fortunately, for many of us, dreaming alone was not enough. These people set about building a toolkit stocked with instruments and techniques to find planets outside our solar system — exoplanets. In turn, these tools help us better understand our place in the Universe.
In October the Nobel Committee awarded the 2019 Nobel Prize in Physics to Michel Mayor, Professor at the Observatory of the Faculty of Science of the University of Geneva (UNIGE), Switzerland, and his doctoral student Didier Queloz for their discovery of 51 Pegasi b in 1995 — which marked the first discovery of an exoplanet orbiting a Sun-like star. The award marked the first time that exoplanet research has scooped what is, arguably, the most prestigious prize in science. Quite fitting as even though 51 Pegasi b was not the first exoplanet to be discovered — that honour goes to Astronomers Aleksander Wolszczan and Dale Frail who discovered an exoplanet around a neutron star in 1992 — it was Mayor and Queloz’s breakthrough that really spurred on the science of exoplanet investigation.
As extraordinary as it sounds, before the 1990s, it wasn’t entirely certain that other stars actually possessed planets of their own. Whilst there was technically no reason to suspect that the solar system was unique, the 1980s had proved a frustrating time for exoplanet hunters. By the turn of that decade, many potential candidates had come and gone evading positive confirmation.
Despite early setbacks, since 1995, the catalogue of exoplanets has soared, with over 4,000 examples now in NASA’s catalogue. And with technology only improving, that collection is set to soar. This animation and sonification from SystemSounds is a stunning representation of how the field has exploded since the 1990s. Created by SYSTEM Sounds (Matt Russo, Andrew Santaguida)
We are becoming so confident in the discovery of exoplanets, that we are now turning our attention to much more detailed examinations of previously discovered examples. For example, many researchers are now focusing on the investigation of exoplanet atmospheres, attempting to discover if they contain traces of chemicals such as carbon monoxide and other organic and complex molecules, and, of course, water. Should these elements be observed it constitutes a clue, a tiny hint, that life may not be unique to our planet.
Thus far, searches for exoplanets have been more effective in finding gas giants, planets similar to Jupiter. But new advances such as the James Webb Space Telescope and the Extremely Large Telescope have researchers salivating at the idea of finding and examining smaller, rocky planets. Planets just like Earth. And of course, the discovery of the Trappist-1 system — containing seven Earth-like rocky planets, three in the so-called ‘habitable zone’ capable of harbouring liquid water — has shown that these planets are definitely out there waiting for us to find them.
As such, exoplanet research stands on the cusp of providing an answer to the question we have all pondered at some point whilst staring at the stars, are we alone in the universe?
Of course, the fact that it took so many years of fruitless searching to begin to successfully spot exoplanets illustrates, these blighters are extremely difficult to observe. This means that astronomers have had to develop extremely precise and sensitive methods of exoplanet detection. These techniques are numerous, each with its own strengths and weaknesses.
It goes without saying that before we spotted the first exoplanet, our experience of observing other planets was restricted to our neighbours in the solar system. This was done exclusively through direct imaging, but this technique becomes much more difficult as the distance to an object increases.
The hindrances imposed on direct imaging increase exponentially when we consider the effect of attempting to spot a dim object next to a much bright one — exactly the scenario faced when attempting to spot a distant planet orbiting its parent star. But, this proximity to an extremely bright object is not always a hindrance to exoplanet detection. In fact, many methods of spotting these planets absolutely depend on it. If a dim object can have an effect of the extremely bright object — then the ability to observe this bright object is a benefit.
This interference arises from the fact that stars with planets orbiting them demonstrate a ‘wobble’ in their motion. This arises from the fact, that despite common belief, planets don’t actually orbit stars. In fact, planets and stars orbit a mutual centre of mass— or barycentre —its location based on the masses of the planets and stars involved. As the usual set-up of a planetary system involves a star that is tremendously more massive than its planets, this mutual point of orbit is usually closer to the star centre of mass — often within the star’s surface.
This huge disparity in mass means that this ‘wobble’ is tiny. As an example, consider our own solar system. As the Sun constitutes more than 99.9% of the total mass of the solar system, the barycentre for our planetary system is located very close to our star’s centre of mass. The most significant gravitational influence on the Sun arises as a result of the solar system’s most mass planet — Jupiter.
Let’s imagine, for simplicity’s sake, that Jupiter is the only planet orbiting the Sun. An observer viewing this reduced solar system and Jupiter’s 12-year orbit from the nearest planetary system — Alpha Centauri, 4.4 light-years away — would see the Sun as a mere point of light. The shift in its position caused by Jupiter would be just 3.7 milliarcseconds. To put this shift into perspective, consider that one pixel in an image from the Advanced Camera for Surveys aboard the Hubble Space Telescope represents 50 milliarcseconds — one pixel! Thus you can see, this ‘wobble’ caused by Jupiter is a tiny, barely perceptible amount of movement, less than 1/10 of a pixel from the nearest star!
Two further things to consider in this hypothetical situation, Jupiter is the most massive planet in the solar system, the wobble caused by Earth viewed from the same position would be smaller by a factor of at least 300. Also, many of the exoplanets that we are attempting to spot are much further afield than 4.4 light-years. That means that any method using this wobble must be incredibly sensitive and precise. Incredibly, despite this tiny effect, the wobble has spawned several methods of exoplanet detection.
One of these methods is astrometry — very effective for detailing high-mass planets in wide orbits around relatively low-mass stars, and thus not well suited to tracking down Earth-like, rocky planets. For an indirect observation method, astrometry is pretty good at pinning down characteristics like mass, and orbital period, shape and width. Unfortunately, it isn’t great at actually identifying planets.
Thankfully there are other indirect techniques that have helped astronomers help find exoplanets — one of which combines a star’s ‘wobble’ with a phenomenon familiar to drivers and pedestrians everywhere.
Sirens, soundwaves and stars. The Doppler Wobble
I’m sure everyone reading this has been in a situation in which an ambulance with sirens blaring has raced towards them, passed their position and continued on its journey. You’ll have likely noticed that as the vehicle approaches the sound of its siren is higher pitched, switching to a lower pitch as it moves away.
This is because as the soundwaves are emitted by the approaching ambulance they are compressed and shorter wavelength sound waves mean a higher-pitched sound. As the siren recedes, the soundwaves are stretched out — resulting in a lower pitch.
This is the Doppler effect, and the key thing for astronomers is, it applies to any kind of wave emitted by a moving object — even light which propagates as a wave. Just as the wavelengths of soundwaves correspond to different pitches, the wavelengths of light correspond to different colours. Longer wavelengths producing a reddening, shorter wavelengths produce bluer light. This is referred to as redshift and blueshift— a crucial phenomenon in astronomy.
Instead of an ambulance, let’s think about a star moving towards us, as the light waves emitted are compressed — causing the light signature of the star to be shifted towards the blue end of the spectrum. As the star moves away, the light is stretched out again — shifting the light signature towards the red end of the electromagnetic spectrum.
If this is the case, why do the lights atop the ambulance as it recedes not appear redder than they were on their approach? This is because the amount of red and blue shift is determined by an object’s speed divided by the speed of light c. As c is so large, an object would have to be moving at tremendous speeds to result in a significant enough change in colour for us to notice.
You might be wondering how exactly scientists can tell that a star’s signature has shifted towards either end of the electromagnetic spectrum. This is because stars don’t emit light in a constant ‘smear’ across the spectrum. There are notable dark bars where light is not emitted — referred to as the absorption spectrum. It is by tracing the shift of these bars that researchers can see if a star is wobbling and by how much, thus inferring the presence of exoplanets.
Of course, you may well have noticed a flaw with this technique. It’s only useful in detecting exoplanets that are causing their star to wobble towards and away from Earth. This gives rise to the method’s alternative name — the radial-velocity method. In addition to this blind-spot in glimpsing planets moving perpendicular to Earth, the Doppler-wobble technique can also only tell us what a planet’s minimum mass is.
But, knowledge of the light signature of a star gives rise to another tool in the exoplanet hunter’s arsenal, one which depends on planets crossing — or transiting — their parent star. The photometry technique.
Don’t cross me!
The photometry technique measures the dip in brightness of a star caused as a planet crosses in front of it, thus allowing us to infer the presence of an exoplanet and even collect details about a few of its characteristics. The method clearly requires searching for rare eclipse events where a planet blocks some of its parent star’s light.
You may be unsurprised to learn that like the other methods detailed above, the photometry technique has to be incredibly sensitive. In this case, that is because the disparity in size between a star and a planet orbiting it is so huge in the star’s favour that the light obscured by this transit is minuscule.
To illustrate this, take a look at this image of Mercury transiting the Sun seen from within the solar system.
This speck, highlighted below, is Mercury. Now imagining the tiny fraction of light this would have obscured. When you’ve done that, imagine viewing this scene from millions of light-years away!
Returning to the example of Jupiter, the largest planet in our solar system, when it transits the Sun it blocks just 1% of the star’s light — making the Sun appear 1% fainter for a period of 12 hours. As small as it is, in comparison to the phenomena exploited by the two methods above this effect is massive.
And again, like its fellow methods of exoplanet detection, the photometric technique has significant limitations that define the situations in which it can be employed. Many planets don’t transit their parent stars and those that do have to be orientated ‘just right’ for the photometry method to work. Also, transits that do occur are incredibly brief, so it takes a lot of good fortune to catch one. That means that the vast majority of exoplanets that we believe exist out there in the depths of space can’t be spotted by this method.
The Earth’s atmosphere and the ‘twinkling effect’ it has on stars is also a major hindrance to the photometry method. This results in its reliance on space-based telescopes. By taking the atmosphere out of the equation, it is possible to not just improve the precision of our measurements but also allows for the continuous monitoring of a star’s brightness without the agony of something as mundane as a rainy-day ruining data.
The future of exoplanet research is extremely bright
With all the limits and drawbacks I’ve listed it may seem like searching for exoplanets is something of a hopeless task, like searching for a needle in a haystack. Except there are 100 billion ‘haystacks’ or stars outside of our analogy in each galaxy. Clearly its a tribute to our advances in science that we have found 4000 or so ‘needles’ thus far.
The astrometry technique, the first tool we examined in the exoplanet hunter’s toolkit isn’t particularly useful, but the second, the doppler technique has been a real boon. It kickstarted exoplanet-hunting as a viable scientific field in the ’90s and provided the majority of discoveries right up into the 2000s. Despite this, its the transit technique — photometry — the last piece of equipment that we turned over, that holds the most promise for the future.
It was a slow starter for sure, reaching maturity much later than the previous two methods mentioned. But, as the use of automated and space-based telescopes has become more prevalent, the ability to keep thousands of stars under constant observation is making the photometry technique the exoplanet-hunting tool that promises to push the boundaries of our understanding of planets elsewhere in the universe.
As our catalogue of exoplanets expands, researchers also now begin to look beyond just spotting these other worlds. The CHEOPS telescope will launch this week (17/12/19) with its mission to spot exoplanets close-by that warrant further investigation. And it is the James Webb Space Telescope, launching in 2021, that will really delve into these selected planets.
Researchers will then use some of the methods I’ve listed above to examine the atmospheres of these planets, a ‘deep-dive’ that would have seemed like little more than a pipe-dream in 1995 when Michel Mayor and Didier Queloz spotted 51 Pegasi b.
Exoplanet research, in many ways, represents one of the ultimate expressions of the drive to perform science. For its pioneers, the men and women that stocked our toolkit, it simply wasn’t enough to lie back staring at the stars, dreaming of other worlds.
After an initial setback yesterday (17/12/19) due to a software error, the European Space Agency’s (ESA) CHaracterising ExOPlanets Satellite — or CHEOPS — telescope has finally launched from the European Spaceport in Kourou, French Guiana.
CHEOPS was aboard a Russian Soyuz-Fregat rocket which blasted off at 9:54 am European time. The Rocket will take approximately 145 minutes to place the CHEOPS unit into a rare pole to pole low-Earth orbit.
The telescope hitched a ride with an Italian radar satellite, the rocket’s primary payload.
CHEOPS is the result of a collaboration between 11 member countries within the ESA, with Switzerland taking the lead on the project. Two of the country’s leading Universities — the University of Geneva and the University Bern — worked together to equip CHEOPS with a state of the art photometer.
This powerful device will measure changes in the light emitted by nearby stars as planets pass by — or transit — them. This examination reveals many details about a planet’s characteristics, its diameter, and details of its atmosphere in particular.
By combining a precise measurement of diameter with a measurement of mass, collected by an alternative method, researchers will then be able to determine a planet’s density. This, in turn, can lead to them deducing its composition and internal structure.
CHEOPS was completed in a short time with an extremely limited budget of around 50-million Euros.
“CHEOPS is the first S-class mission for ESA, meaning it has a small budget and a short timeline to completion,” explains Kate Issak, an ESA/CHEOPS project researcher. “Because of this, it is necessary for CHEOPS to build on existing technology.”
CHEOPS: Informed by the past, informing the future
The project is acting as a kind of ‘middle-man’ between existing exoplanet knowledge and future investigations. It is directed to perform follow-up investigations on 400–500 ‘targets’ found by NASA planet-hunter Transiting Exoplanet Survey Satellite (Tess) and its predecessor, the Kepler observatory. Said targets will occupy a size-range of approximately Earth-Neptune.
This mission then fits in with the launch of the James Webb Telescope in 2021 and further investigation methods such as the Extremely Large Telescope array in the Chilean desert, set to begin operations in 2026. It will do this by narrowing down its initial targets to a smaller set of ‘golden targets’. Thus, meaning its investigation should help researchers pinpoint exactly what planets in close proximity to Earth are worthy of follow-up investigation.
“It’s very classic in astronomy that you use a small telescope ‘to identify’, and then a bigger telescope ‘to understand’ — and that’s exactly the kind of process we plan to do,” explains Didier Queloz, who acted as chair of the Cheops science team. “Cheops will now pre-select the very best of the best candidates to apply to extraordinary equipment like very big telescopes on the ground and JWST. This is the chain we will operate.”
Queloz certainly has pedigree when it comes to exoplanets. The astrophysics professor was jointly awarded the 2019 Nobel Prize in Physics for the discovery of the first exoplanet orbiting a Sun-like star with Michel Mayor.
The first task of the science team operating the satellite, based out of the University of Bern, will be to open the protective doors over the 30 cm aperture telescope — thus, allowing CHEOPS to take its first glimpse of the universe.
The scheduled launch of the European Space Agency’s (ESA) Characterizing Exoplanets Satellite or CHEOPS telescope, set to usher in a new era of exoplanet research was cancelled today.
The launch, which was set to take place at 12:54 am local time (roughly 4am ET) from the spaceport in Kourou, French Guiana was called-off due to what the University of Bern is calling a software error. The institution was set to live stream the event.
The launch has been rescheduled and is expected to take place within the next 24 to 48 hours. The official revised launch time and date will be announced at 6:00pm (ET).
CHEOPS is loaded aboard a Russian Soyuz-FG, which will place it in a low-Earth orbit. The procedure — which will take around 145 minutes to complete — will result in CHEOPS taking a rare pole-to-pole orbit.
The CHEOPS mission is designed to observe exoplanets in relatively close proximity to Earth. The aim of this is to select viable targets for future investigation by the next major development in both the fields of astronomy and exoplanet research — the James Webb Telescope, set to launch in 2021.
It is hoped that by using a combination of these instruments, researchers will finally be able to uncover characteristics of rocky exoplanets, which has been tricky up until now. This will include discovering if such bodies can maintain atmospheres and deduce the chemical compositions of these atmospheres.
It is likely that when the launch does occur, live coverage will be provided by the ESA on its website.
Exoplanet researcher Ignas Snellen — a professor in astronomy at the University of Leiden in the Netherlands — has collected the 2019 Hans Sigrist prize for his innovative work in the field of exoplanet research. The award of the prize to Snellen comes at the conclusion of a year which also marked the Nobel Committee’s recognition of the first observation of an exoplanet orbiting a Sun-like star, awarding its discoverers Michel Mayor and Didier Queloz the 2019 Nobel Prize in Physics.
The message from the scientific community seems to be clear, exoplanet research is a field to watch. With the launch of the CHEOPS satellite, later this month and the James Webb Space Telescope set to launch in 2021, applied science is finally catching up to aspirations held by astronomers for decades–the discovery of more and more diverse worlds outside our solar system.
In addition to this, the tantalizing possibility of catching a fleeting glimpse of a clue that we are not alone in the universe seems closer than ever to realization.
But as Snellen explains, things could have been very different for him, falling into exoplanet research was something of a happy accident: “I was doing very different research, working with galaxies,” he says. “I didn’t really know where my research was going. That’s when I was asked to present a workshop on extrasolar planets.”
Despite the serendipity at play, Snellen says he recognised the potential growth for the young field almost immediately. “I thought ‘wow, what an amazing field!'”
And Snellen’s decision to pursue exoplanet research relates indirectly to Nobel prize winners Mayor and Queloz. “This was in 2001, so exoplanet research was still in its infancy, but the first transiting exoplanet had been discovered as well as a few others.”
Despite the fact that only a handful of exoplanets had been discovered when Snellen began his research in the field less than two decades ago, NASA’s catalog of extrasolar planets now numbers in excess of 4,000. Clearly, this is a stunning illustration of just how rapidly the field has advanced in this relatively short period of time.
Snellen’s work focuses on assessing the atmospheric composition of exoplanets. This possible to do when a planet passes in front of–or ‘transits’– its parent star. The planet’s atmosphere absorbs light from the star at certain wavelengths. As chemical elements absorb and emit light at certain frequencies, the resulting light spectrum forms a distinct ‘fingerprint’ by which they can be identified.
This method of transit spectroscopy holds great promise in terms of identifying potential ‘biomarkers’ such as molecular oxygen, water and carbon monoxide.
As the Hans Sigrist Prize is specifically designated to recognize scientists in the midst of their careers rather than acting as a ‘lifetime achievement’ type award, it is only fitting that its recipient should very clearly have their eyes on future goals. And, fortunately, the future is bright for exoplanet research.
The ESO’s CHEOPS telescope launches on 17th December with its mission to identify nearby, small rocky exoplanets. Snedden points out the mission’s role as an important first step in the exoplanet research, helping select targets for researchers to further investigate.
But the two projects that Snellen is most excited for and the launch of the James Webb Telescope in 2021 and the completion of the aptly named 39-meter diameter Extremely Large Telescope (ELT) scheduled for completion in 2025.
“At the moment we can only observe the atmospheres of large Jupiter-like gas giants,” he explains. “The James Webb will finally allow us to start examining the atmospheres of smaller, rocky, more Earth-like exoplanets.”
These planets will still differ quite a bit from Earth, elaborates Snellen, explaining that they will, for example, be much hotter than our planet. “The exciting thing is, we don’t yet know if these small rocky planets can actually hold an atmosphere,” Snellen says.
The researcher concludes by pointing out that the seven Earth-like planets of the Trappist-1 system are very likely the first targets for further investigation. An exciting prospect, given that at least three of these planets are believed to exist in that system’s ‘habitable zone’–an area where water can exist as a liquid, a key ingredient for life.
One of the most promising prospects for discovering liquid water in the Trappist-1 system is Trappist-1e, an exoplanet that is slightly denser than Earth. As liquid water requires a temperature that is not too hot and not too cold, and also a certain amount of pressure–the fact that Trappist-1e receives roughly the same amount of radiation from its star as Earth and its gravitational influence exerts a similar pressure, it seems a safe bet to predict liquid water will be found there.
Of course, the concept of discovering liquid water amongst the stars and drawing comparisons to Earth leads, inevitably to the question could any of these planets also host life?
Snellen urges caution, remarking that even if these biomarkers are found, it is still a long way from confirming the ‘Holy Grail’ of exoplanet research: the presence of extraterrestrial life.
“It would be a major clue,” Snellen points out. “But it’s too simple to say ‘OK we have molecular oxygen, this is a sign of life.’ As molecular oxygen is difficult to detect though, by the time we can identify it, we should also be able to see lots of other gases.”
The Hans Sigrist Prize was established in 1994 to recognise mid-career scientists who still have a significant time left in their careers to make further major contributions to their field. Thus far, two of the previous recipients have gone on to become Nobel Prize Laureates later in their careers.
In connection with the prize, Snellen will receive 100,000 CHF–around $100,000–to help further his research. Accepting his prize, Snellen first thanked the team of researchers that have supported him in his research over the past decade.
Researchers from the University of Bern have discovered that the Earth would be approximately 5% larger if it were hot and molten rather than rocky and solid. Pinpointing the difference between rocky exoplanets and their hot, molten counterparts is vital for the search for Earth-like exoplanets orbiting stars outside the solar system.
The fact that rocky exoplanets that are approximately Earth-sized are small in comparison to other planets, makes them notoriously difficult for astronomers to spot and characterise. Identification of a rocky exoplanet around a bright, Sun-like star will likely not be plausible until the launch of the PLATO mission in 2026. Thankfully, spotting Earth-size planets around cooler and smaller stars such as the red dwarfs Trappist-1 or Proxima b is currently possible.
But, searching for molten exoplanets could help astronomers probe the darkness of space — and identify Earth-sized rocky-exoplanets around stars like our own.
“A rocky planet that is hot, molten, and possibly harbouring a large, outgassed atmosphere ticks all the boxes,” says Dan Bower, an astrophysicist at the Center for Space and Habitability (CSH) of the University of Bern. “Such a planet could be more easily seen by telescopes due to strong outgoing radiation than its solid counterpart.”
Learning more about these hot, molten worlds could also teach astronomers and astrophysicists more about how planets such as our’s form. This is because rocky planets such as the Earth are built from ‘leftovers of leftovers’ — material not utilised in either the formation of stars or giant planets.
“Everything that doesn’t make its way into the central star or a giant planet has the potential to end up forming a much smaller terrestrial planet,” says Bower: “We have reason to believe that processes occurring during the baby years of a planet’s life are fundamental in determining its life path.”
This drove Bower and a team of colleagues mostly from within the Planet S network to attempt to discover the observable characteristics of such a planet. The resulting study — published in the journal Astronomy and Astrophysics — shows that a molten Earth would have a radius 5% or so larger than the actual solid counterpart. They believe this disparity in size is a result of the differences in behaviour between solid and molten materials under the extreme conditions generated beneath the planet’s surface.
As Bower explains: “In essence, a molten silicate occupies more volume than its equivalent solid, and this increases the size of the planet.”
This 5% difference in radii is something that can currently be measured, and future advances such as the space telescope CHEOPS — launching later this year — should make this even easier.
In fact, the most recent collection of exoplanet data suggests that low-mass molten planets, sustained by intense starlight, may already be present in the exoplanet catalogue. Some of these planets may well then be similar to Earth in regards to the material from which they are formed — with the variation in size no more than the result of the different ratios of solid and molten rock.
Bower explains: They do not necessarily need to be made of exotic light materials to explain the data.”
Even a completely molten planet would fail to explain the observation of the most extreme low-density planets, however. The research team suggest that these planets form as a result of molten planets releasing — or outgassing — large atmospheres of gas originally trapped within interior magma. This would result in a decrease in the observed density of the exoplanet.
Spotting such outgassed atmospheres of this nature should be a piece of cake for the James Webb Telescope if it is around a planet that orbits a cool red dwarf — especially should it be mostly comprised of water or carbon dioxide.
The research and its future continuation have a broader and important context, points out Bower. Probing the history of our own planet, how it formed and how it evolved.
“Clearly, we can never observe our own Earth in its history when it was also hot and molten. But interestingly, exoplanetary science is opening the door for observations of early Earth and early Venus analogues that could greatly impact our understanding of Earth and the Solar System planets,” the astrophysicist says. “Thinking about Earth in the context of exoplanets, and vice-versa offers new opportunities for understanding planets both within and beyond the Solar System.”
Original research: Dan J. Bower et al: Linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations, Astronomy & Astrophysics. DOI: https://doi.org/10.1051/0004-6361/201935710
A rocky extrasolar moon brimming with lava could orbit a planet 550 light-years from Earth, astronomers led by researchers from Bern University have discovered.
The volcanically active exomoon could be hidden in the exoplanet system WASP-49b, orbiting a hot giant planet in the inconspicuous constellation of Lepus, underneath the bright Orion constellation.
The researchers describe the exomoon as an ‘extreme’ version of Jupiter’s moon Io — the most volcanically active body in our own solar system. Thus, painting a picture of an exotic and dangerous world — an ‘exo-Io’.
Apurva Oza, a postdoctoral fellow at the Physics Insitute of the University of Bern and associate of the NCCR PlanetS, describes the exomoon, comparing it to a famous sci-fi setting: “It would be a dangerous volcanic world with a molten surface of lava — a lunar version of close-in Super-Earths like 55 Cancri-e.
“A place where Jedis go to die, perilously familiar to Anakin Skywalker.”
More than a grain of sodium. Uniting theory and circumstantial evidence.
Astronomers have yet to discover a moon beyond our solar system meaning that the researchers base their suspicions of the existence of this exo-Io on circumstantial evidence — namely sodium gas in WASP-49b at an unusually high-altitude.
Oza explains: “The neutral sodium gas is so far away from the planet that it is unlikely to be emitted solely by a planetary wind.
“The sodium is right where it should be.”
Comparing this feature to observations of the Jupiter and Io system using low-mass calculations demonstrated to the team that an exo-Io could, indeed, be a plausible mechanism for sodium at WASP-49b.
The theory that large amounts of sodium around an exoplanet could point to a hidden moon or a ring of material was advance by Bob Johnson and Patrick Huggins in 2006. Following this, researchers from the University of Virginia calculated that a three-body system comprised of a star, close giant planet and a moon could remain stable for billions of years.
Oza took these theoretical predictions to form the basis of he and his colleagues’ work — published in the Astrophysical Journal.
The astrophysicist explains: “The enormous tidal forces in such a system are the key to everything.
“The energy released by the tides to the planet and its moon keeps the moon’s orbit stable, simultaneously heating it up and making it volcanically active.”
The researchers also demonstrate in their study that a small rocky moon would eject more sodium and potassium into space via this extreme volcanism than a large gas planet. This would especially be the case at high altitudes.
These emissions can then be identified by astronomers using the technique of spectroscopy. These particular elements are particularly useful to astronomers.
Oza adds: “Sodium and potassium lines are quantum treasures to us astronomers because they are extremely bright.
“The vintage street lamps that light up our streets with yellow haze, is akin to the gas we are now detecting in the spectra of a dozen exoplanets.”
When comparing their calculations with actual observations of sodium and potassium, the team found five candidate systems where a hidden exomoon could survive thermal evaporation. In the case of WASP-49b, the best explanation for the observed data was the presence of an exo-Io.
This isn’t the only explanation, however. As mention above, the observations of sodium at high altitudes could instead indicate the exoplanet is surrounded by a ring of material — most likely ionised gas.
Oza admits that the team need to find more clues, and as such, are relying on future observations with both ground and space-based telescopes. Also, as a few of these exo-Ios could eventually be destroyed as a result of extreme mass-loss, the team also want to search for evidence of such destruction.
Oza concludes: “While the current wave of research is going towards habitability and biosignatures, our signature is a signature of destruction.
“The exciting part is that we can monitor these destructive processes in real-time, like fireworks.”
Some exoplanets could have better conditions for life to thrive than Earth itself, according to a new study that used computer modeling to explore the conditions that could exist on different types of exoplanets.
“This is a surprising conclusion,” said lead researcher Dr. Stephanie Olson, “it shows us that conditions on some exoplanets with favorable ocean circulation patterns could be better suited to support life that is more abundant or more active than life on Earth.”
The search for life outside the solar system has been accelerated by the discovery of exoplanets. As they can’t be explored by space probes because of the distances involved, scientists are working with remote tools such as telescope to understand conditions there.
With her team, Olson used software called ROCKE-3D developed by NASA’s Goddard Institute for Space Studies to model rocky exoplanets. They modeled a range of different exoplanets to explore which would be the most likely to develop and sustain life, based on ocean circulation.
They found that thicker atmospheres combined with slower rotation rates and the presence of continents all produced higher upwelling rates. The research was presented at the Goldschmidt Geochemistry Congress in Barcelona.
“NASA’s search for life in the Universe is focused on the so-called ‘habitable zone’ planets, which are worlds that have the potential for liquid water oceans. But not all oceans are equally hospitable—and some oceans will be better places to live than others due to their global circulation patterns,” Olson said.
Previous research has shown that salty oceans are likely to exist beyond the Solar System. In addition to Earth, Mars was once rather watery for example and there are moons that appear to harbor liquid oceans. But these nearby worlds don’t meet the criteria laid out by the research, though.
Mars is dry and has a thin whisper of an atmosphere, and the moons so far researched have barely any atmospheres as well; we’re also currently unsure of their continental status. But there are a lot more exoplanets out there in the galaxy than there are moons in the Solar System.
The first criterion that has so far been used in the search for habitable exoplanets has been whether a planet is in the “habitable zone” — where temperatures are not so hot that liquid oceans would boil, nor so cold that they would freeze. This new research adds some parameters that could be employed in future searches.
“In our search for life in the Universe, we should target the subset of habitable planets that will be most favorable to large, globally active biospheres,” Olson said, “because those are the planets where life will be easiest to detect – and where non-detections will be most meaningful.”
The use of ultraviolet flares from red suns and biofluorescence may provide astronomers with vital life signs in the universe
A new method of searching for life in the cosmos has been pioneered by astronomers from Cornell University.
The team propose that astronomers could utilise harsh ultraviolet radiation flares from red suns — once thought to destroy surface life on planets — to assist in the discovery of hidden biospheres. The team’s study — published in the journal Monthly Notices of the Royal Astronomical Society — suggests that ultraviolet radiation could trigger biofluorescence — a protective glow — from life on exoplanets.
Jack O’Malley-James, a researcher at Cornell’s Carl Sagan Institute and the study’s lead author, says: “This is a completely novel way to search for life in the universe.
“Just imagine an alien world glowing softly in a powerful telescope.”
Some undersea coral on Earth use a similar form of biofluorescence that the team intend to utilise in the search for life. The coral does this in order to render the sun’s harmful ultraviolet radiation into harmless visible wavelengths, in the process, creating a beautiful radiance.
“Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them,” points out Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute.
She points out that in our search for exoplanets, we have searched for ones which look like our own planet. This research plays off the idea the biofluorescence may not have evolved on Earth exclusively.
In fact, as this is a form of defence from harsh UV radiation, logic suggests that its usefulness — and thus, the chance of development — would be increased around stars where UV flares are commonplace.
A large fraction of exoplanets — planets beyond our solar system — reside in the habitable zone of M-type stars. This type of star — the most commonly found in the universe — frequently flare, and when those ultraviolet flares strike their planets, biofluorescence could paint these worlds in beautiful colours.
The next generation of Earth- or space-based telescopes can detect the glowing exoplanets — should they exist.
Ultraviolet rays are transformed into less-energetic and therefore less harmful wavelengths through a process called “photoprotective biofluorescence.” This should leave a very specific signal which astronomers can search for.
Kaltnegger continues: “Such bio fluorescence could expose hidden biospheres on new worlds through their temporary glow when a flare from a star hits the planet.”
The astronomers used emission characteristics of common coral fluorescent pigments from Earth to create model spectra and colours for planets orbiting active M stars to mimic the strength of the signal and whether it could be detected for life.
Proxima b — a potentially habitable world found orbiting the active M star Proxima Centauri in 2016 could qualify as a target for such a search. The rocky exoplanet has been one of the most optimal space travel destinations due to the proximity of the star it orbits — although such jaunts are a concern for the far-future.
Jack O’Malley-James, continues: “These biotic kinds of exoplanets are very good targets in our search for exoplanets, and these luminescent wonders are among our best bets for finding life on exoplanets.”
Large, land-based telescopes that are being developed now for 10 to 20 years into the future may be able to spot this glow.
Kaltenegger concludes: “It is a great target for the next generation of big telescopes, which can catch enough light from small planets to analyze it for signs of life, like the Extremely Large Telescope in Chile.”
It may be an infant, but that doesn’t mean it’s small. Researchers have discovered a new ‘baby’ planet, at least twice the size of Jupiter, carving a path through a stellar nursery.
Astrophysicists from Monash University have used the ALMA telescope in Chile to discover a ‘baby’ planet inside a protoplanetary disc. But despite being a youngster, this infant is still between two to three times the mass of Jupiter — the most massive planet in our solar system.
The giant ‘baby’ was found inside in the middle of a gap in the gas and dust that forms the planet-forming disc around the young star HD97048. The study — published in Nature Astronomy — is the first to provide an origin of these gaps in protoplanetary discs — also known as ‘stellar nurseries’ because they act as the birthplaces for planets— which have thus far puzzled astronomers.
“The origin of these gaps has been the subject of much debate,” says the study’s lead author, Dr Christophe Pinte, an ARC Future Fellow at the Monash School of Physics and Astronomy. “Now we have the first direct evidence that a baby planet is responsible for carving one of these gaps in the disc of dust and gas swirling around the young star.”
The team discovered the new planet by mapping the flow of gas around HD97048 — a young star not yet on the main sequence, which sits in the constellation Chamaeleon located over 600 light-years from Earth.
Observing the flow in this material, the team hunted for areas in which the flow was disturbed, in a similar way to disturbance a submerged rock would cause in a stream flowing over it. They were able to ascertain the planet’s size by recreating this ‘bump’ or ‘kink’ in the flow using computer models.
Using the same method of locating ‘bumps’ in gas flow around young stars, the team previously discovered a similar new ‘baby’ planet around another young star roughly a year ago. Those findings were published in the Astrophysical Journal Letters.
That initial discovery — found in the stellar nursery around HD163296 360 light-years from Earth — was the first of its kind and provided a ‘missing link’ in scientists understanding of planet formation.
These two studies add to what is only a small collection of known ‘baby’ planets.
“There is a lot of debate about whether baby planets are really responsible for causing these gaps,” says Associate Professor Daniel Price, the study’s co-author and Future Fellow at the school. “Our study establishes for the first time a firm link between baby planets and the gaps seen in discs around young stars.”
Remember the Boaty McBoatface incident? Well, the Internet is trying its digital hand at naming things again, and this time it’s for NASA’s latest exciting discovery: the 7 new exoplanets of the Trappist system. Twitter users have come up with a wonderful mix of suggestions ranging from trollish or tongue-in-cheek, all the way to some that might actually have some merit as potential names for the planets.
Image credits NASA.
The Internet doesn’t have the best track record when it comes to naming things. Just last March, UK’s Natural Environment Research Council (NERC) invited people to vote on what name their newest arctic research vessel should be christened with. NERC went with RRS Sir David Attenborough in recognition to the world famous UK naturalist and broadcaster — but that’s not what the public voted for. Oh no.
After former BBC Radio Jersey presenter James Hand jokingly suggested the council should go with Boaty McBoatface, the suggestion picked up a huge number of votes, quickly becoming the most popular name. Thankfully for the NERC, they announced from the beginning that the poll was non-binding in nature so they could opt for what they considered a “more appropriate” name.
Just last month, NASA announced the discovery of seven exoplanets in the Trappist system, three of which lie in the Goldilocks zone of potential habitability. Currently named Trappist-1b to h, the planets’ permanent nomenclature will be decided by the International Astronomical Union — but the opportunity to name them was too good for the collective creativity of the Internet to pass up on, and people are tweeting their ideas under the hashtag 7NamesFor7NewPlanets. Some suggestions are simply funny, we’ve seen some nods to cultural references, and some names that actually sound pretty good. And surely enough, “Planet McPlanetface” made it in the suggestions.
Here are some of the highlights, starting with the funnies.
There’s also a lot of cultural referencing going on, with the names of great houses from Game of Thrones being suggested, the dwarfs’ names in Snow White, as well as nods to the Harry Potter books. But this one I enjoyed the most:
Some users view the christenings as an opportunity to those who have sacrificed in humanity’s efforts to reach for the stars — several tweets call for the planets to be named for the seven astronauts who lost their lives aboard the Challenger in 1986.
So will these suggestions actually make it on the star charts? Probably not.
“The TRAPPIST #7NamesFor7NewPlanets was a trending hashtag that was started by Twitter users, and we were simply joining an existing conversation by posting the current scientific names with the hashtag. We are not collecting suggestions, and we rely on the IAU’s process for the naming of these planets,” NASA’s Social Media Manager John Yembrick told me in an e-mail.
Seeing the generally light-hearted and humorous way these names are being suggested on Twitter, it’s unlikely that the IAU will actually go with any of them. But there are some good contenders tweeted under the hashtag, so the union may still surprise us in the end. Which means there’s still a tiny hope for Pluto.
Author’s note: Corrected the article after receiving NASA’s Social Media Manager John Yembrick’s email. Initially, it stated NASA started the hashtag to ask for suggestions for the new names; 1:50 am EET.
We humans have a lot of reason to be proud. In the short span of a few million years we have become self-aware and clever, learning to manipulate our world in ways that have greatly enhanced our survival. The last 100,000 years have seen the evolution of anatomically modern humans, which migrated from our African birthplace to colonize and populate essentially all corners of the globe. Using sophisticated brains we learned about the world, deciphering patterns in nature, designed and constructed tools, and formed societies and civilizations.
Unfortunately, there has also been much about our success that is less praiseworthy. At the same time that we have been building ingenious devices to better feed, clothes, shelter, and move ourselves from point A to point B, we have also been in the business of making ever more efficient weapons to destroy one another. As our technological progress seems to outpace our societal ethics and maturity, we now have it in our power to completely annihilate our entire species. In the not too distant future it could conceivably be possible to extinguish all life on planet earth, whether through horrible accident or intentional destruction.
While we sit on this world powder cake of self destruction, perhaps at times in a little more danger, and at times in a little less, we often wonder if we are alone in the universe. Not only are we the only example of intelligent life that we know of in the universe, but our little planet is home to the only example of life we know of anywhere. All evidence seems to indicate that there are a vast number of planetary systems and potential habitable worlds in the universe. We have detected over 2000 exoplanets, so far, with the first one being discovered only as recently as 1992, and with advancing techniques the numbers have been skyrocketing in recent years. Yet, there is still no sign of alien life, and even with SETI (Search for Extraterrestrial Intelligence) listening for alien radio transmissions since 1960, we have not detected any confirmed signs of intelligent aliens.
A few of the exoplanets that the Kepler space telescope has discovered orbiting other stars.
In the October 23, 2015 issue of The International Journal of Astrobiology, authors Adam Stevens, Duncan Fogan, and Jack O’Malley James, make an interesting case that we may soon have the technology necessary to detect alien civilizations in the act of self-destruction. In fact, alien armageddon may provide us with our most likely opportunity to detect the presence of intelligent alien life – even if we are only witness to their last moments. The authors summarize some of the possible ways that an intelligent civilization could go horribly wrong, and how evidence for these tragic events could potentially be detected by our instruments here on earth.
The first major scenario would be that of global nuclear war. There are several characteristics of a world that has been annihilated by an intense exchange of nuclear weapons that might be detectable from our distant vantage point. The detonation of the devices would emit high energy gamma radiation that would last for a short period of time – on the order of thousandths of a second. Even given the high energy involved in the detonation of a world arsenal of nuclear devices, it is not very likely we could detect the energy output from so many light years away. Naturally occurring gamma ray bursts (GRBs) are some of the most intense energy generating events in the universe, and can be observed at the edges of the visible universe, but they are also around 10 billion billion billion times more energetic than the predicted energy release of all the nuclear weapons on earth combined.
The intense radiation from global nuclear war would, however, ionize the planet’s atmosphere, resulting in an “air glow” due to light emission from energized nitrogen and oxygen. The atmosphere would have a lovely green glow in the the visible spectrum, is predicted to last several years, and could be observed as an increase in the light intensity at the expected wavelength. There would also be a depletion of the planet’s ozone layer as reactive chemicals are produced by the explosions. This too, might be observable as a change in the planet’s atmosphere. Nuclear war would also generate a great deal of dust and small particles that enter the air, altering the transparency of the atmosphere. A combination of a gamma ray burst, air glow, drop in ozone concentration, and loss of transparency of the atmosphere would be good evidence for this alien-made disaster. Any one event on its own might not be enough evidence to be certain of an artificial event. For example, a change in the atmosphere from transparent to opaque could also be caused by natural events like a large asteroid impact.
Second on the list for a self-induced civilization-stopping calamity would be use of potent biological weapons. Genetically engineered organisms, like viruses and bacteria, would potentially be much more deadly than any naturally occurring epidemic. If the infectious agent was designed to attack all animals and plants, the entire biosphere would be jeopardized. How would such a horror be detected by us? Well, a rapid demise of the planet’s multicellular life would result in a huge amount of organic material for bacteria to consume. The result of this massive decay would be the release of certain chemicals such as methane and ethane, that could be observed by spectroscopic analysis of the atmosphere.
Artistis depiction of an exoplanet surface in a distant solar system.
The next deadly scenario is the so called, “grey goo” event. This involves the engineering of self-replicating nanomachines – tiny machines that use some building material as substrate and convert it into more tiny nanomachines. The authors of the paper point out that this could be the result of either “goodbots” or “badbots”. In the goodbot case the self-replicating nanomachines were never intended for destruction, but due to poor system controls, got out of hand leading to world destruction. Badbots, on the other hand, were designed to cause complete and total destruction – the ultimate doomsday machine! These replicators would take all carbon containing material on the planet’s surface, (ie. living organisms), and convert them into a growing mass of more replicators that do the same. K. Eric Drexler – who coined the term nanotechology- pointed out in his ‘Engines of Creation’: “Replicators can be more potent than nuclear weapons: to devastate Earth with bombs would require masses of exotic hardware and rare isotopes, but to destroy all life with replicators would require only a single speck made of ordinary elements.”
It might take as little as a few weeks to convert the worlds living biomass into a lifeless desert of tiny replicators – grey goo! Pretty scary!! From earth we might be able to detect this as a large increase in atmospheric dust (the masses of nanomachines). The nanomachines would form giant sand dunes (bot dunes in this case) and would change the apparent brightness of the planet as we observe it. There would be visual effects of shadowing, as the planet orbits its star due to the changing angle that light hits the grains of nanomachines in the bot dunes. This is similar to the effect we see as light passes through the small particles in Saturn’s rings at different angles. Over a period of thousands of years the nanomachines would be recycled through the planet’s interior, as the planet’s normal geological processes continue to operate.
Another apocalyptic possibility would be intentional pollution of the planet’s star. To dispose of harmful radioactive waste, a civilization might launch such materials into its parent star. Detecting uncommon radioactive elements in the star’s atmosphere would be evidence for this unnatural process. Carl Sagan, called this “salting” the star. We would know that this was an artificial process by the fact that elements present would be produced only in such high amounts by nuclear processes that don’t occur naturally. Models have shown that if this was carried out to extremes, it would affect the star’s internal balance of forces and cause it’s size to increase, while dropping the surface temperature. This change in the star’s characteristics could change the location of the habitable zone around the star, making life difficult or impossible on the alien planet that did the salting. The authors suggest that, “compiling a sample of stars that are bright, cool, and slightly larger than expected as an initial step to search for this particular death channel.”
Finding evidence for intelligent life in the cosmos would radically change our view of ourselves, and our place in the universe. If aliens have a similar psychology to ourselves (a big if to be sure), they could be prone towards potentially fatal flaws that could escalate to total catastrophe. Their demise at their own hands (or equivalent body structures) might also be the signal that informs us that they were ever there at all. Finding one or more civilizations that self-destructed might also give us a way to prognose the long-term health of the human race. Do civilizations reach a point where their technological power is too great for their wisdom? Could Homo sapiens one day end up as a signal to the stars that we were here for a brief time, an intelligent species, but just not quite intelligent enough to solve the problem of surviving peacefully with one another? Journal Reference: