Most planets in this universe are spherical, and for good reason. Forces of gravity generally pull equally from all sides, from the center to the edges like the spokes of a bicycle wheel. This makes the overall shape of a planet a sphere. Some can be more spherical than others (Earth is flattened at the poles and bulges at the equator) depending on their distance from the sun and speed of rotation, but generally all are alike.
However, the European Space Agency’s exoplanet mission Characterizing Exoplanets Satellite (Cheops) has revealed a planet with a deformed shape more like that of a rugby ball than a sphere. This planet, coined WASP-103b and which has a density 1.5 times that of Jupiter, is located in the Hercules constellation approximately 1,225 light-years away from our oblate spheroid home.
“It’s incredible that Cheops was actually able to reveal this tiny deformation,” says Jacques Laskar of Paris Observatory, Université Paris Sciences et Lettres, and co-author of the research. “This is the first time such analysis has been made, and we can hope that observing over a longer time interval will strengthen this observation and lead to a better knowledge of the planet’s internal structure.”
The deformation is caused by gravitational tugs from WASP-103, its host star. The planet lies a mere 1.8 million miles away from WASP-103, which is both hotter and 1.5 times larger than our Sun (by comparison, Earth is around 93 million miles from the Sun). Astronomers have suspected that such close proximity would cause monumental tides, but up until now they haven’t been able to measure them.
Using new data from Cheops, which measures exoplanet transits — the dip in light caused when a planet passes in front of its star from our point of view — along with data already obtained by the Hubble Space Telescope and Spitzer Space Telescope, researchers were able to detect how tidal forces deform the exoplanet from a usual sphere into the rugby ball shape.
The team was able to utilize the transit light curve of WASP-103b to obtain a boundary—the Love number—that determines how mass is distributed within a planet. Understanding how mass is distributed can reveal details on the internal structure of the planet.
“The resistance of a material to being deformed depends on its composition,” explains Susana Barros of Instituto de Astrofísica e Ciências do Espaço and University of Porto, Portugal, and lead author of the research. “For example, here on Earth we have tides due to the Moon and the sun but we can only see tides in the oceans. The rocky part doesn’t move that much. By measuring how much the planet is deformed we can tell how much of it is rocky, gaseous or water.”
When they calculated the Love number for WASP-103b, the researchers discovered an exoplanet larger than our Solar System’s largest inhabitant, which suggested that the internal structure is similar, despite the exoplanet having almost twice the radius.
“In principle, we would expect a planet with 1.5 times the mass of the Jupiter to be roughly the same size, so WASP-103b must be very inflated due to heating from its star and maybe other mechanisms,” Susana said. “If we can confirm the details of its internal structure with future observations maybe we could better understand what makes it so inflated. Knowing the size of the core of this exoplanet will also be important to better understand how it formed.”
While it’s fairly certain that WASP-103b isn’t the only deformed planet out there, it is the most conclusive evidence to date. Researchers hope that further work, including from the James Webb Space Telescope, can provide more certainty on where those might lie within the vast universe.
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.
The European Space Agency’s (ESA) space telescope CHEOPS (CHaracterising ExOPlanet Satellite) begins its journey into space aboard the Soyuz rocket on December 17th. In preparation for the launch from French Guiana, collaborators in the mission, the ESA, the University of Geneva and the University of Bern held a press conference on the morning of the 5th December.
The gathered experts from the respective agencies discussed the mission–the ESA’s first ‘S-Class’ or small scale project–the international collaboration that brought it together and the role CHEOPS will play in the investigation of Exoplanets and the search for life elsewhere in the universe.
“After over six years of intensive work, I am, of course very pleased that the launch is finally in sight,” Willy Benz, CHEOPS’s principal investigator and professor of astrophysics at the University of Bern states.
The main role of CHEOPS will be to examine the ever-growing catalog of exoplanets, explains David Ehrenreich, CHEOPS Consortium Mission Scientist from the University of Geneva.
This involves selecting what Ehrenreich describes as ‘golden targets’ or exoplanets that missions such as the James Webb Space Telescope (JWST)–set to launch in 2021 from the same site—can follow-up on in order to perform in-depth examinations. As the JWST will search for signs of habitability–mainly indications of water and methane– it is a massive advantage for it to have preselected targets to study.
CHEOPS will enforce this selection process by examining nearby bright stars that are known to host exoplanets–particularly those with planets in a size range of Earth to Neptune. By measuring the transit depths as these planets cross their host star–the sizes of the planets can be accurately ascertained and then the researchers can also calculate their density and in turn, their composition–if they are rocky or gaseous, for example. The mission should also be able to determine if the planets possess deep oceans–believed to be a key component for the development of life.
A Small Mission Can Answer Big Questions
Kate Issak, a CHEOPS project scientist from the ESA explains how the mission–the first part of the Cosmic Vision 2015-2025 program–differs from previous endeavors undertaken by the agency: “CHEOPS is the first S-class mission for ESA, meaning it has a small budget and a short timeline to completion.
“Because of this, it is necessary for CHEOPS to build on existing technology.”
The cost of CHEOPS is an estimated 50-million Euros and it has taken 5 years to complete after being greenlit in 2014. Whilst this may not seem like a small amount of money or a short period of time, the cost and preparation time of the JWST–about 9 billion Euros and 7 years–very much puts both into perspective.
But neither a short timeline to completion or a small budget nor the fact that it mainly bridges the gap between past and future investigations will stop CHEOPS from attempting to answer some of the biggest lingering questions in exoplanet research.
Ehrenreich lays out some of the big questions that CHEOPS may have the potential to tackle, namely:
How do planets form?
At what rate do planets occur around other stars?
What are the compositions of these planets?
How do these compositions compare with the compositions of planets in the solar system?
Is our solar system unique or common?
And perhaps most interestingly for the general public and scientists alike:
Are any of these worlds habitable?
By tackling these questions CHEOPS and the ESA really get to the heart of both space exploration and exoplanet investigation.
CHEOPS: Empathising collaboration
As is fitting for a mission that probes such fundamental ideas as, how common is life in the universe, the ESA is throwing the use of the CHEOPS equipment out to other institutions and researchers.
Whilst 80% of CHEOPS’s operating time will be determined by the ESA’s mission program, Issak explains, the remaining 20% will be devoted to the wider scientific community. The projects and researchers that will be able to make use of this time will be determined based on merit alone.
“CHEOPS will build on the work of the consortium and benefit the scientific community as a whole,” promises Issak.
The idea of community spirit is built into CHEOPS’s DNA from its genesis, Willy Benz the mission’s principal investigator explains. The project brings together 11 individual nations each of which has made a specific contribution to the equipment aboard the satellite.
Issak adds “CHEOPS is an excellent example of how EU member states can work together.”
The ESA will follow-up on CHEOPS with PLATO (PLAnetary Transits and Oscillation of stars) project in 2026, and ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission in 2028.
Plato will specialise in the examination of rocky exoplanets orbiting in habitable zones around Sun-like stars, particularly focusing on the potential for these planets to hold liquid water. It will also examine seismic activity in stars–giving insight into the age and evolutionary stage of these planetary systems.
Ariel, meanwhile, will take exoplanet survey and characterisation to a whole new level of detail, enable to perform chemical censuses of a wide variety of planet’s atmospheres.
As the award of this year’s Nobel Prize in Physics to Michel Mayor and Didier Queloz for the discovery of the first exoplanet around a Sun-like star demonstrates, the search for exoplanets and the quest to categorise and understand them is currently one of the hottest research areas in science.
As such CHEOPS puts the ESA at the forefront of the race to discover how common our home planet and the solar system is, and potentially, answer an age-old question: are we alone in the Universe?
In 2018, NASA’s Kepler Space Telescope mission came to a predictable end after it ran out of fuel some 94 million miles from Earth. During its nine-year planet-hunting mission, Kepler discovered nearly 3,000 exoplanet candidates and more than 2,600 confirmed exoplanets in our galaxy, cementing the notion that our solar system isn’t all that special. So far, 55 exoplanets that are potentially habitable — meaning they orbit their stars at just the right distance that may allow water to flow on the surface — have been found, of which 20 are Terran or Earth-sized.
There are at least as many planets as there are stars in the galaxy
After studying thousands of exoplanets astronomers are now confident that:
Relatively small planets are common;
There are likely more planets than stars in the galaxy;
Planets and planetary systems are extremely diverse;
No exoplanets similar to Earth in size, distance, and type of star they orbit have been found.
“I think that exoplanets tell us about our place in the universe. That’s probably the main reason the discovery of the first exoplanets were awarded the Nobel Prize in Physics this year. We are seeing just how diverse planets are. Planets are more common than they were thought to be before the first exoplanets were found. The number of planets in our galaxy is at least as large as the number of stars. But while planets and planetary systems are so diverse, planets like Earth may be very, very rare,” Dr. Jack Lissauer, a scientist at the NASA Ames Research Center and co-investigator of the Kepler mission, told ZME Science at the World Science Forum in Budapest. The World Science Forum is a biannual international conference on global science policy, which is affiliated with UNESCO and ICSU.
An exoplanet is any planet orbiting a star other than the Sun. Just 24 years ago, we only knew of planets in our solar system — but not for lack of trying. Detecting exoplanets is very challenging because they’re much smaller and fainter than stars. Since exoplanets are not self-luminous, scientists had to think outside the box.
The most successful exoplanet detection method is transit photometry, which looks for periodic, repetitive dips in the visible light of stars caused by planets passing, or transiting, in front of them. Essentially, a transit is just a partial eclipse.
“It was getting all the precision to detect the small variations in the light of the stars for planetary transits. To be able to detect planets — actually the smallest one that we’ve found was about the size of Earth’s moon, it’s the smallest planet known,” Lissauer said.
This has led to some incredibly unexpected discoveries that exceeded even our wildest expectations. Planets such as Kepler-22b, which is a water world between the size of Earth and Neptune located more than 600 light-years away or Kepler-16b, which is part of a ‘Tatooine-like’ system 200 light-years away — it is home to the largest planet ever discovered orbiting two stars. Then there’s the exciting Kepler-11 system, home to no fewer than six planets and the fullest, most compact planetary system yet discovered beyond our own.
“A year before that, or even eight months before that, no multi-planetary transiting system had been discovered. By the time of Kepler-11 discovery, there were two others. One had three planets, one had two planets, Kepler-11 had six. And we were able to derive the masses of the inner five by the perturbations they gave on one another so the transits were not periodic. It contains five of the lowest mass exoplanets at the time for which we had measurements of both their size and their mass, so we could have good estimates of what they’re made of, by getting their density,” Lissauer told ZME Science.
The car-sized telescope was launched primarily to detect small planets. For this purpose, it was designed to find out how many planets are out there not by observing the entire galaxy but by taking a sample in and near the habitable zone — the region at the right distance from the star so that the surface has liquid water.
Although it has been decommissioned, Kepler’s legacy lives on. Scientists are still sifting through thousands of candidate exoplanets, a task which will keep them busy for many years to come. Kepler has also shaped future missions such as the Transiting Exoplanet Survey Satellite, or TESS.
Launched in April 2018, TESS is NASA’s latest planet hunter. Its mission is to survey planets orbiting 200,000 of some of the brightest stars close to Earth. Later, planets identified by TESS can be inspected for a closer look by the upcoming James Webb Telescope.
“I’m a co-investigator on TESS as well as Kepler and I think of Kepler as having done great science by detecting these very small planets — planets not hugely different from Earth in their properties, in some cases,” Lissauer said.
“TESS won’t detect planets as small and as long-period orbits as Kepler — it has much smaller cameras — but it detects planets around brighter stars. So, the purpose of TESS is really finding planets around very bright stars so there’s enough light from these stars that we can detect light passing through their thin atmosphere where they transit their stars. So, TESS is enabling us — with other instruments, especially the James Webb Telescope, which will be launched in two years, and some of the very large and extremely large telescopes on the ground — to study the composition of the atmospheres of mid-sized exoplanets. Not Earth analogs — that’s too difficult — but not these hot Jupiters. So, planets a big step closer to our own,” he added, explaining TESS’ major role in future planet-hunting efforts.
Besides TESS, there are exciting exoplanet-hunting missions. Europe’s CHaracterising ExOPlanets Satellite (CHEOPS) mission is destined to launch in December. Its mission is to that of a follow-up: it will be tasked with studying stars known to harbor planets, rather than surveying the sky in search of new ones.
By performing observations of multiple planetary transits, CHEOPS will be able to provide more precise measurements of a planet’s size, which can be combined with existing mass determinations to render accurate densities. Knowing these parameters, it is possible to determine the exoplanet’s composition and discriminate between Earth-like planets where life may blossom and other types of Earth-mass planets that challenge our current notions of habitability.
In 2026, ESA will launch PLATO, which is short for the PLAnetary Transits and Oscillations of stars) mission. PLATO is designed to find and determine the properties of Earth-like planets that orbit the habitable zone around stars similar to the Sun. For the first time, PLATO will allow scientists to calculate accurately the properties of a large number of stars with planets, including their ages.
Meanwhile, ESA’s ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission is destined to study and characterize exoplanets, rather than discover them. ARIEL is scheduled to launch in 2028. The mission is designed to perform high-accuracy transit, eclipse, and phase-curve multiband observations of exoplanets. Scientists are confident that ARIEL will be able to provide a complex picture of the chemical nature of its targeted exoplanets, but also their host stars. This will allow researchers to investigate the nature of these exoplanets, how they formed, and how they evolved.
Kepler opened the gate for mankind’s exploration of the cosmos, and its successors are bound to offer even more surprises. There are billions — perhaps trillions — of stars in the Milky Way galaxy alone and, on average, each of those stars has at least one planet orbiting them. However, there really is no place like home.
“We only have Earth. It’s possible that there are other planets like Earth out there but even if they are very similar, they are very far away. We can’t do a migration. We can’t solve our problem as the Irish did in the late 1800s to solve the potato famine. We would be like Easter Island. If we don’t take care of this planet, we are toast! All the mass extinctions in the last 5 million years are coincident with the rise of CO2 in the atmosphere of our planet. We must stop this crazy behavior. We can’t just say something has to be done. We have to do things ourselves. We have to cut our carbon footprint,” Lissauer told the audience during an event at the 2019 World Science Forum, held between 20-24 November.