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This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)

Astronomers discover an exoplanet system with rhythm

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.

This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star. New research by Adrien Leleu and his colleagues with several telescopes, including ESO’s Very Large Telescope, has revealed that the system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits.  But while the orbital motion in this system is in harmony, the physical properties of the planets are more disorderly, with significant variations in density from planet to planet. This contrast challenges astronomers’ understanding of how planets form and evolve. This artist’s impression is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)
This artist’s impression shows the view from the planet in the TOI-178 system found orbiting furthest from the star based on the known physical parameters for the planets and the star as seen and using a vast database of objects in the Universe. (ESO/L. Calçada/spaceengine.org)

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.

This animation shows a representation of the orbits and movements of the planets in the TOI-178 system. In this artist’s animation, the rhythmic movement of the planets around the central star is represented through a musical harmony, created by attributing a note (in the pentatonic scale) to each of the planets in the resonance chain. This note plays when a planet completes either one full orbit or one-half orbit; when planets align at these points in their orbits, they ring in resonance. (ESO/L. Calçada)

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.

This artist’s animation shows the view from the planet in the TOI-178 system found orbiting furthest from the star, with the inner planets visible in the background. This animation is based on the known physical parameters for the planets and the star seen, and uses a vast database of objects in the Universe. (
ESO/L. Calçada/spaceengine.org)

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.

The astronomers used the transit method that measures tiny dips in light to spot the exoplanets (NASA)

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.

Original Research

A. Leleu, Y. Alibert, N. C. Hara, et al, ‘Six transiting planets and a chain of Laplace resonances in TOI-178,’ Astronomy & Astrophysics, [2021], (doi: 10.1051/0004-6361/202039767).

NASA’s exciting announcement: They’ve discovered an Earth-like planet in the habitable zone

Planet Kepler-452b: the first near-Earth-size world to be found in the habitable zone of a star that is similar to our Sun. This extremely exciting announcement was made by NASA today; while this doesn’t mean that the planet is inhabited, it does mean that it has many of the characteristics that our own Earth-Sun system has, and the odds of it hosting life seem significant.

The sweep of NASA Kepler mission’s search for small, habitable planets in the last six years. The first planet smaller than Earth, Kepler-20e, was discovered in December 2011 orbiting a Sun-like star slightly cooler and smaller than our sun every six days. But it is scorching hot and unable to maintain an atmosphere or a liquid water ocean. Kepler-22b was announced in the same month, as the first planet in the habitable zone of a sun-like star, but is more than twice the size of Earth and therefore unlikely to have a solid surface. Kepler-186f was discovered in April 2014 and is the first Earth-size planet found in the habitable zone of a small, cool M dwarf about half the size and mass of our sun. Kepler-452b is the first near-Earth-Size planet in the habitable zone of a star very similar to the sun.
Credits: NASA Ames/W. Stenzel

The first exoplanet orbiting another star like our sun was discovered in 1995; it seems almost incredible to think that just 21 years ago, exoplanets, especially Earth-like planets, were science fiction. Today, thousands of discoveries later, we know better.

The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus, but the planet itself is quite old – 6 billion years old, 1.5 billion years older than our sun. While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer, and the planet is just 5% farther away from its star than the Earth is from the Sun.

“The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth,” said Paul Hertz, NASA’s Astrophysics Division director at the agency’s headquarters in Washington. “Future NASA missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind’s quest to find truly Earth-like worlds.”

Its size is also known – Kepler-452b is 60 percent larger in diameter than Earth, being considered a “super Earth”. It’s a rocky planet just like Earth, but we don’t yet know its composition. What we do know is that while bigger, Kepler-452b has a 385-day orbit, only 5 percent longer than ours.

“We know of just one planet where life exists — Earth. When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth,” said Elisa Quintana, research scientist at the SETI Institute at NASA’s Ames Research Center in Moffett Field, Calif., and lead author of the paper published today in the journal Science. “Finding a habitable zone planet comparable to Earth in size is a major step forward.”

This artist’s concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water — an essential ingredient for life as we know it — to pool on the surface. Credits: NASA Ames/JPL-Caltech/T. Pyle

But as exciting as this announcement is, it’s important to remember that there is no clear indication that the planet might host life. We know nothing of the temperature and (potential) atmosphere of the planet, and these are decisive factors. It’s these two that will determine whether or not this is a true Earth twin, or only a distant cousin.

“Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has,” said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames, and co-author of the paper. “Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth.”

But even finding a “cousin” of Earth is still remarkable, especially when you consider where we’ve come in 25 years; one can only wonder, where will we be another 25 years from now?

Artist's impression of a view from the HD 7924 planetary system looking back toward our sun. Credit: Karen Teramura & BJ Fulton, University of Hawaii, Institute for Astronomy

Automated process finds three super-Earths in our neighborhood – a new way to hunt for alien planets

Using three state of the art ground-based telescopes, a team of astronomers has identified three super-Earth exoplanets seven to eight times as massive as our own planet and orbit their parent star closer than Mercury orbits the sun. What’s hot about the findings – apart from the planet’s likely scorching surface – is that these were made using a novel automated approach, in which one telescope called the Automated Planet Finder (APF) Telescope at Lick Observatory in California was programmed to scour the night’s sky and look for signs of nearby alien planets. These three planets are just the beginning of a new process that will hopefully return hundreds of planets in our neighborhood, all without the need for human supervision.

Artist's impression of a view from the HD 7924 planetary system looking back toward our sun.  Credit: Karen Teramura & BJ Fulton, University of Hawaii, Institute for Astronomy

Artist’s impression of a view from the HD 7924 planetary system looking back toward our sun. Credit: Karen Teramura & BJ Fulton, University of Hawaii, Institute for Astronomy

To find the new planets, scientists at UC Berkeley detected the wobble of the star HD 7924 as the planets orbited and pulled on the star gravitationally. APF and Keck Observatory in Hawaii traced out the planets’ orbits around the over many years using the Doppler technique that has successfully found hundreds of mostly larger planets orbiting nearby stars. APT made crucial measurements of the brightness of HD 7924 to assure the validity of the planet discoveries.

Most of the planets discovered outside our solar system are about the size of Neptune or bigger most of which are called Hot Jupiters since they’re similar in size to Jupiter (several hundred times the mass of Earth) and usually orbit a very hot star. If we’re to find life on other planets or find one that’s hospitable enough to cater for life (why not bring ourselves in…), the best chance we have according to researchers is to look for those planets that are similar to Earth in terms of mass, density and orbit around the parent star. Of course, these aren’t mandatory conditions – it’s just that this is a proven system we’ve confirmed right in our backyard. Preferably, you also want to track planets that are located nearby, say in the 100-light-years range. This is where the APF comes in.

Tracing planets in the nightsky can be very difficult, tiresome and prone to error. It took many years to train the computers to run the observations by themselves, but we’re finally seeing the first results. Next, this proven system will be used for a pilot two-year search with the APF.

“This level of automation is a game-changer in astronomy,” said Andrew Howard, a professor of astronomy at the University of Hawaii. “It’s a bit like owning a driverless car that goes planet-shopping.”

“When the survey is complete we will have a census of small planets orbiting sun-like stars within approximately 100 light-years of Earth,” says University of Hawaii at Manoa graduate student Benjamin “BJ” Fulton.

“We initially used APF like a regular telescope, staying up all night searching star to star. But the idea of letting a computer take the graveyard shift was more appealing after months of little sleep. So we wrote software to replace ourselves with a robot,” BJ continued.

Findings appeared in the Astrophysical Journal.

Super-dense celestial bodies may be new types of planet

Despite all the magnificent advancements in the field, we are still in the infancy of our research on extraterrestrial planets, so it shouldn’t really surprise anybody if a new type of planet is found.

neptune stripped

Mysterious dense bodies outside the Solar System which have puzzled astronomers for quite a while may in fact be remnants of Neptune-like planets which went too close to their Sun and got compressed.

NASA’s Kepler space mission to find exoplanets, which launched in 2009 found bodies which appeared to be simply too heavy for their size – the planets in case have radiuses similar to Earth’s, but are denser than pure iron. No conventional planet forming theory can explain this.

“There is no way to explain that in the Solar System,” says Olivier Grasset, a geophysicist at the University of Nantes in France.

Grasset and his team put forth an interesting theory which claims that these planets are actually fossil remains of much larger bodies, which were stripped of their outer, frozen crust – leaving us today with the fossil core.

If these planets were formed far from their stars, but in time, migrated closer to their star – possibly as cloe as Mercury is today, then the hot temperatures of the star would evaporate the outer layers of the planet, which are made mostly from volatile elements (hydrogen, helium and water). The only thing that would remain would be the core (consisting of rock and metal, just like Earth’s) – which is very dense, because during its initial stage (before the outer layers were evaporated) it was formed at about 5 million times atmospheric pressure on Earth and temperatures of approximately 6000 Celsius degrees.

Lars Stixrude, a geologist at University College London, calls the idea “fascinating”, but he does mention that we still don’t understand the behaviour of materials under the extreme temperatures and pressures of an ice-giant core is still incomplete. William Borucki, a space scientist at NASA’s Ames Research Center in Moffett Field, California, and leader of the Kepler mission adds that the theory is plausible, but there are plenty of other ways through which the outer layers could be blasted away. The process could be the result of a cataclysmic collision with another planet-sized object, for example. Either way, the Kepler mission is definitely updating how we understand the Universe we live in.

“This is why we do science.”, Borucki says.

Super Earth planet

Super-earth planets might have a magnetic field from liquid metals

Super Earth planet

Of the hundreds of exoplanets discovered thus far, many of them are classed as super-Earths, planets with a mass up to ten times that of our planet. Due to their inherent different structure however, their cores would be far from being similar to that of the Earth, leading many scientist to claim that they might not have a magnetic field. A team of researchers  University of Rochester has shown, however, that a flowing liquid metal might generate magnetic dynamos in super-Earths.

While our planet’s atmosphere is rather thick, it is not at the front line in the war against deadly cosmic radiation. This role is played by the sheltering magnetic field that fends off radiation and makes the Earth a paradise for life. This magnetic field – and that of Mercury, the only other rocky planet known to have a magnetic field – stems from the constant motion of its molten iron core.

Super-Earths on the other hand, because of their extreme mass, would present large viscosities and high melting temperatures at their core. This means that they can’t support a magnetic field.

That is, as the researchers very well put it, if you apply what you know about the Earth to other planets as well. This process of reason works in most cases, however when dealing with totally alien environments, phenomenons that don’t occur in our own back yard might escape scientists.

“For many decades we have usually imagined terrestrial planets — the Earth, its neighbors such as Mars, and distant super-Earths — as all having Earth-like properties: that is, they have a outer shell or mantle composed of nonmetallic oxides, and an iron rich core which is metallic and from which planetary magnetic fields originate,” said R. Stewart McWilliams, a geophysicist at the Carnegie Institution of Washington.

“This rule is central to our thinking about super-Earths, yet it is clearly anthropocentric — that is, we are applying what we know from our own observations on Earth to remote planets for which we can observe very little — and, as for many anthropocentric ideas, we are finding that more imagination is needed to understand such alien worlds.”

Extreme conditions at the core of super-Earths

The researchers  found the magnesium oxide, a common ceramic material found on Earth, can transform into liquid when subjected to the extreme conditions such as those found in the interior of super-Earths. Magnesium’s highly resistant to changes when under intense pressures and temperature, and theoretical predictions claim that it has just three unique states with different structures and properties present under planetary conditions.

To see how the material might perform in extreme conditions on alien worlds, the researchers aimed a high-pulsating laser, that shoots beams in just a billionth of a second, to heat a magnesium oxide sample to temperatures as high as 90,000 degrees Fahrenheit (50,000 Celsius), also squeezing it in the process to pressures 14 million times that of normal Earth atmospheric pressure.   They watched this rocky substance change to a solid with a new crystal structure, and finally into a liquid metal. In the melting process, the material changes its properties radically, going from an electrical insulator into a material that allows electrons to flow easily through it, allowing a magnetic field to form.

“Our results show that the usual assumption that planetary magnetic fields originate exclusively in iron cores is too limiting,” McWilliams said. “Magnetic fields might also form within planetary mantles. In fact, this idea has been speculated on for decades, but now we have hard data to show that, indeed, such a ‘mantle-dynamo’ is plausible.”

Previous theories regarding magnesium oxide said that the material may exist in only three states with different structures and properties present under planetary conditions –  solid under ambient conditions (such as on the Earth’s surface), liquid at high temperatures, and another form of solid at high pressure . This last structure had never been observed until now.

The implications of these findings suggest that the metallic, liquid phase of magnesium oxide could well exist today in the deep mantles of super-Earth planets, as well as the newly-observed solid phase. This means that they might very well harbor a magnetic field which might protect its surface from radiation and allow life to blossom.

“It is often said that life on planets may require the presence of a strong magnetic field to protect organisms from dangerous radiation from space such as cosmic rays — at least this may be true for certain types of life, similar to humans, that live on a planet’s surface,” McWilliams said. “We find that magnetic fields may occur on a wider range of planets than previously thought, possibly creating unexpected environments for life in the universe.”

“Everyone, both scientists and the public, should keep in mind that super-Earths are, and probably will remain for some time, a big mystery,” McWilliams said. “It is easy to speculate as to their properties — to draw a picture of one, for example — but quite difficult to make certain conclusions such as we have for our own Earth. This is both exciting and daunting — there are many possibilities to explore, but scientists have much work to do. We hope the public has a lot of patience.”

Findings were reported in the journal Science.

 

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

How many Earth-like planets are there in the Milky Way? Billions, according to astronomers

One of the most outstanding dreams astronomers and other scientists hope to accomplish is to someday encounter proof that extraterestrial life exists. Intelligent life might be extremely far off, however microbiological life should without a doubt be present elsewhere other than our planet or solar system. For life to blossom, however, the right conditions have to be met, and one of the major prerequisites for life supporting conditions is liquid water. Along the years, scientists have come up with what’s called the habitable zone, an area around a star’s orbit where favorable conditions for harboring life may exist. Now, after hundreds of potential Earth-life planets have been found, scientists have enough data at their disposal to elaborate a statistical hypothesis – there are billions of planets similar to Earth that might potentially support life in our galaxy alone!

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

Astronomers using the European Southern Observatory’s HARPS, a high precision instrument fitted to the 3.6m telescope at the Silla Observatory in Chile, studied 102 red dwarf stars neighbouring the sun over a period of six years. Red dwarfs are smaller and cooler than the sun, however it’s been found that 40% of red dwarf stars may have Earth-sized planets orbiting them that have the right conditions for life.

“Our new observations with Harps mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” said team leader Xavier Bonfils from the Observatoire des Sciences de l’Univers de Grenoble, France.

“Because red dwarfs are so common – there are about 160 billion of them in the Milky Way – this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

During their survey, the group of astronomers found a total of nine super-Earths, planets with a rocky structure that have a mass up to ten times that of Earth, while two such planets are orbiting inside their stars’ habitable zones. Extrapolating with data gathered from non-dwarf stars were super-Earths have also been found, the scientists were able to produce an estimate for how common different sorts of planets are around red dwarf.

Huge planets, the size of Jupiter for instance, have been found to orbit in less than 12% of red dwarfs, suggesting their much rarer than small rocky words, like the Earth. Alright, but why should we care if there’s another potential Earth out there if its thousands of light years away? Well, the scientists found that there could be at least 100 super-Earths’ orbiting in the habitable zones of their stars, located in a radius 30 light years away from our own sun. That’s not that far at all, in the astronomical scale.

The group’s findings were reported in the journal Astronomy and Astrophysics.

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