Posted on by Matt Williams

“Monster Planet” Discovered, Makes Scientists Rethink Theories of Planetary Formation

Artist’s impression of the cool red star and gas-giant planet NGTS-1b against the Milky Way. Credit: University of Warwick/Mark Garlick.

When it comes to how and where planetary systems form, astronomers thought they had a pretty good handle on things. The predominant theory, known as the Nebular Hypothesis, states that stars and planets form from massive clouds of dust and gas (i.e. nebulae). Once this cloud experiences gravitational collapse at the center, its remaining dust and gas forms a protoplanetary disk that eventually accretes to form planets.

However, when studying the distant star NGTS-1 – an M-type (red dwarf) located about 600 light-years away – an international team led by astronomers from the University of Warwick discovered a massive “hot Jupiter” that appeared far too large to be orbiting such a small star. The discovery of this “monster planet” has naturally challenged some previously-held notions about planetary formation.

The study, titled “NGTS-1b: A hot Jupiter transiting an M-dwarf“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team was led by Dr Daniel Bayliss and Professor Peter Wheatley from the University of Warwick and included members from the of the Geneva Observatory, the Cavendish Laboratory, the German Aerospace Center, the Leicester Institute of Space and Earth Observation, the TU Berlin Center for Astronomy and Astrophysics, and multiple universities and research institutes.

Artist’s impression of the cool red star above NGTS-1b. Credit: University of Warwick/Mark Garlick.

The discovery was made using data obtained by the ESO’s Next-Generation Transit Survey (NGTS) facility, which is located at the Paranal Observatory in Chile. This facility is run by an international consortium of astronomers who come from the Universities of Warwick, Leicester, Cambridge, Queen’s University Belfast, the Geneva Observatory, the German Aerospace Center, and the University of Chile.

Using a full array of fully-robotic compact telescopes, this photometric survey is one of several projects meant to compliment the Kepler Space Telescope. Like Kepler, it monitors distant stars for signs of sudden dips in brightness, which are an indication of a planet passing in front of (aka. “transiting”) the star, relative to the observer.  When examining data obtained from NGTS-1, the first star to be found by the survey, they made a surprising discovery.

Based on the signal produced by its exoplanet (NGTS-1b), they determined that it was a gas giant roughly the same size as Jupiter and almost as massive (0.812 Jupiter masses). Its orbital period of 2.6 days also indicated that it orbits very close to its star – about 0.0326 AU – which makes it a “hot Jupiter”. Based on these parameters, the team also estimated that NGTS-1b experiences temperatures of approximately 800 K (530°C; 986 °F).

The discovery threw the team for a loop, as it was believed to be impossible for planets of this size to form around small, M-type stars. In accordance with current theories about planet formation, red dwarf stars are believed to be able to form rocky planets – as evidenced by the many that have been discovered around red dwarfs of late – but are unable to gather enough material to create Jupiter-sized planets.

Artist’s concept of Jupiter-sized exoplanet that orbits relatively close to its star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech)

As Dr. Daniel Bayliss, an astronomer with the University of Geneva and the lead-author on the paper, commented in University of Warwick press release:

“The discovery of NGTS-1b was a complete surprise to us – such massive planets were not thought to exist around such small stars. This is the first exoplanet we have found with our new NGTS facility and we are already challenging the received wisdom of how planets form. Our challenge is to now find out how common these types of planets are in the Galaxy, and with the new NGTS facility we are well-placed to do just that.”

What is also impressive is the fact that the astronomers noticed the transit at all. Compared to other classes of stars, M-type stars are the smallest, coolest and dimmest. In the past, rocky bodies have been detected around them by measuring shifts in their position relative to Earth (aka. the Radial Velocity Method). These shifts are caused by the gravitational tug of one or more planets that cause the planet to “wobble” back and forth.

In short, the low light of an M-type star has made monitoring them for dips in brightness (aka. the Transit Method) highly impractical. However, using the NGTS’s red-sensitive cameras, the team was able to monitored patches of the night sky for many months. Over time, they noticed dips coming from NGTS-1 every 2.6 days, which indicated that a planet with a short orbital period was periodically passing in front of it.

Artist’s impression of the planet orbiting a red dwarf star. Credit: ESO/M. Kornmesser

They then tracked the planet’s orbit around the star and combined the transit data with Radial Velocity measurements to determine its size, position and mass. As Professor Peter Wheatley (who leads NGTS) indicated, finding the planet was painstaking work. But in the end, its discovery could lead to the detection of many more gas giants around low-mass stars:

“NGTS-1b was difficult to find, despite being a monster of a planet, because its parent star is small and faint. Small stars are actually the most common in the universe, so it is possible that there are many of these giant planets waiting to found. Having worked for almost a decade to develop the NGTS telescope array, it is thrilling to see it picking out new and unexpected types of planets. I’m looking forward to seeing what other kinds of exciting new planets we can turn up.”

Within the known Universe, M-type stars are by far the most common, accounting for 75% of all stars in the Milky Way Galaxy alone. In the past, the discovery of rocky bodies around stars like Proxima Centauri, LHS 1140, GJ 625, and the seven rocky planets around TRAPPIST-1, led many in the astronomical community to conclude that red dwarf stars were the best place to look for Earth-like planets.

The discovery of a Hot Jupiter orbiting NGTS-1 is therefore seen as an indication that other red dwarf stars could have orbiting gas giants as well. Above all, this latest find once again demonstrates the importance of exoplanet research. With every find we make beyond our Solar System, the more we learn about the ways in which planets form and evolve.

Every discovery we make also advances our understanding of how likely we may be to discover life out there somewhere. For in the end, what greater scientific goal is there than determining whether or not we are alone in the Universe?

Further Reading: UofWarwick, RAS, MNRAS

Posted on by Matt Williams

Astronomers Find Comets Orbiting a Star 800 Light-Years Away

An artist’s conception of a view from within the Exocomet system KIC 3542116.. Credit: Danielle Futselaar

In the past thirty years, thousands of extra-solar planets have been discovered beyond our Solar System. For the most part, they have been detected by the Kepler Space Telescope using a technique called Transit Photometry. For this method, astronomers measure periodic dips in a star’s brightness – which are the result of planets passing in front of them relative to an observer – to confirm the presence of planets.

Thanks to a new research effort conducted by a team of professional and amateur astronomers, something much smaller than planets were recently detected orbiting a distant star. According to a new study published by the research team, six exocomets were observed orbiting around KIC 3542116, a spectral type F2V star located 800 light years from Earth. These comets are the smallest objects to date detecting the Transit Photometry method.

The study which details their findings, titled “Likely Transiting Exocomets Detected by Kepler“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Saul Rappaport of MIT’s Kavli Institute for Astrophysics and Space Research, the team also consisted of amateur astronomers, members of the Harvard-Smithsonian Center for Astrophysics (CfA), the University of Texas, Northeastern University, and NASA’s Ames Research Center.

Artist’s impression of an orbiting swarm of dusty comet fragments around Tabby’s Star. Credit: NASA/JPL-Caltech

This is the first time that Transit Photometry has been used to detect object as small as comets. These comets were balls of ice and dust – comparable in size to Halley’s Comet – that were found to be traveling at speeds of about 160,934 km/h (100,000 mph) before they vaporized. The researchers were able to detect them by picking out their tails, the clouds of dust and gas that form when comets get closer to their star and begin to sublimate.

This was no easy task, since the tails managed to obscure only about a tenth of 1% of the star’s light. As Saul Rappaport, who is also the professor emeritus of physics at the Kavli Institute for Astrophysics and Space Research, explained in an MIT press release:

“It’s amazing that something several orders of magnitude smaller than the Earth can be detected just by the fact that it’s emitting a lot of debris. It’s pretty impressive to be able to see something so small, so far away.”

Credit for the original detection goes to Thomas Jacobs, an amateur astronomer who lives in Bellevue, Washington, and is a member of Planet Hunters. This citizen scientist project was first established by Yale University and consists of amateur astronomers who dedicated their time to the search for exoplanets. Members are given access to data from the Kepler Space Telescope in the hopes that they would notice things that computer algorithms might miss.

NASA’s Kepler space telescope was the first agency mission capable of detecting Earth-size planets. Credit: NASA/Wendy Stenzel

Back in January, Jacobs began scanning four years of data obtained during Kepler‘s main mission. During this phase, which lasted from 2009 to 2013, Kepler scanned over 200,000 stars and conducted measurements of their light curves. After five months of sifting through the data (on March 18th), he noticed several curious light patterns amid background noise coming from KIC 3542116. As Jacobs said:

“Looking for objects of interest in the Kepler data requires patience, persistence, and perseverance. For me it is a form of treasure hunting, knowing that there is an interesting event waiting to be discovered. It is all about exploration and being on the hunt where few have traveled before.”

Specifically, Jacobs was searching for signs of single transits, which are not like those that are caused by planets orbiting a star (i.e. periodic). While looking at KIC 3542116, he noticed three single transits, and then alerted Rappaport and Andrew Vanderburg, as astrophysicist at University of Texas and member of the CfA. Jacobs had worked with both men in the past, and wanted their opinion on these findings.

As Rapport recalled, the process of interpreting the data was challenging, but rewarding. Initially, they noted that the lightcurves did not resemble those caused by planetary transits, which are characterized by a sudden and sharp drop in light, followed by a sharp rise. In time, Rapport noted the asymmetry in the three lightcurves resembled those of disintegrated planets, which they had observed before.

Artist’s impression of the Epsilon Eridani system, showing Epsilon Eridani b (a Jupiter-mass planet) and a series of asteroid belts and comets. Credit: NASA/SOFIA/Lynette Cook.

“We sat on this for a month, because we didn’t know what it was — planet transits don’t look like this,” said Rappaport. “Then it occurred to me that, ‘Hey, these look like something we’ve seen before’… We thought, the only kind of body that could do the same thing and not repeat is one that probably gets destroyed in the end. The only thing that fits the bill, and has a small enough mass to get destroyed, is a comet.”

Based on their calculations, which indicated that each comet blocked out about one-tenth of 1% of the star’s light, the research team concluded that the comet likely disintegrated entirely, creating a dust trail that was sufficient to block out light for several months before it disappeared. After conducting additional observations, they also noted three more transits in the same time period that were similar to the ones noticed by Jacobs.

The fact that these six exocomets appear to have transited very close to their star in the past four years raises some interesting questions, and answering them could have drastic implications for extra-solar research. It could also advance our understanding of our own Solar System. As Vanderburg explained:

“Why are there so many comets in the inner parts of these solar systems? Is this an extreme bombardment era in these systems? That was a really important part of our own solar system formation and may have brought water to Earth. Maybe studying exocomets and figuring out why they are found around this type of star… could give us some insight into how bombardment happens in other solar systems.”

This artist’s conception illustrates a storm of comets around a star near our own. Credit: NASA/JPL-Caltech

Between 4.1 and 3.8 billion years ago, the Solar System also experienced a period of intense comet activity known as the Late Heavy Bombardment. During this time, asteroids and comets are believed to have impacted bodies in the inner Solar System on a regular basis. Interestingly, this period of heavy bombardment is believed to be what was responsible for the distribution of water to Earth and the other terrestrial planets.

As noted, KIC 3542116 belongs to the spectral type F2V, a yellow-white class of star that is typically 1 to 1.4 times as massive as our Sun and quite bright. Since it is comparable in size and mass to our Sun, it is possible that the bombardment period it is experiencing is similar to what the Solar System went through. Watching it unfold could therefore tell us much about how similar activity influenced the evolution of our Solar System billions of years ago.

In addition to the study’s significance to the study of astrophysics and astronomy, it also demonstrates the important role citizen scientists play today. Were it not for the tireless work performed by Jacobs, who sifts through Kepler data between working his day job and on the weekends, this discovery would not have been possible.

“I could name 10 types of things these people have found in the Kepler data that algorithms could not find, because of the pattern-recognition capability in the human eye,” said Rappaport. “You could now write a computer algorithm to find this kind of comet shape. But they were missed in earlier searches. They were deep enough but didn’t have the right shape that was programmed into algorithms. I think it’s fair to say this would never have been found by any algorithm.”

In the future, the research team expects that the deployment Transiting Exoplanet Survey Satellite (TESS) – which will be led by MIT – will continue to conduct the type of research performed by Kepler.

Further Reading: MIT, MNRAS

Posted on by Matt Williams

Project Blue: Building a Space Telescope that Could Directly Observe Planets Around Alpha Centauri

Artist's concept of the Project Blue space telescope, which the organization hopes to use to spot exoplanets in Alpha Centauri beginning in 2020. Credit: projectblue.org

In the past few decades, thousands of exoplanets have been discovered in neighboring star systems. In fact, as of October 1st, 2017, some 3,671 exoplanets have been confirmed in 2,751 systems, with 616 systems having more than one planet. Unfortunately, the vast majority of these have been detected using indirect means, ranging from Gravitational Microlensing to Transit Photometry and the Radial Velocity Method.

What’s more, we have been unable to study these planets up close because the necessary instruments do not yet exist. Project Blue, a consortium of scientists, universities and institutions, is looking to change that. Recently, they launched a crowdfunding campaign through Indiegogo to finance the development of a space telescope that will start looking for exoplanets in the Alpha Centauri system by 2021.

In addition to its commercial and academic partners, Project Blue is a collaborative effort between the BoldlyGo Institute, Mission Centaur, the SETI Institute, and the University of Massachusetts Lowell. It is steered by a Science & Technology Advisory Committee (STAC) composed of science and technology experts who are dedicated to space exploration and the search for life in our Universe.

Artist’s impression of a planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Credit: ESO

To accomplish their goal of directly studying exoplanets, Project Blue is seeking to leverage recent changes in space exploration, which include improved instruments and methodology, the rate at which exoplanet have been discovered in recent years, and increased collaboration between the private and public sector. As SETI Institute President and CEO Bill Diamond explained in a recent SETI press statement:

“Project Blue builds on recent research in seeking to show that Earth is not alone in the cosmos as a planet capable of supporting life, and wouldn’t it be amazing to see such a planet in our nearest neighboring star system? This is the fundamental reason we search.”

As noted, virtually all exoplanet discoveries that have been made in the past few decades were done using indirect methods – the most popular of which is Transit Photometery. This method is what the Kepler and K2 missions relied on to detect a total of 5,017 exoplanet candidates and confirm the existence of 2,470 exoplanets (30 of which were found to orbit within their star’s habitable zone).

This method consists of astronomers monitoring distant stars for periodic dips in brightness, which are caused by a planet transiting in front of the star.  By measuring these dips, scientists are able to determine the size of planets in that system. Another popular technique is the Radial Velocity (or Doppler) Method, which measures changes in a star’s position relative to the observer to determine how massive its system of planets are.

Project Blue’s mission concept, showing the telescope, its launch and deployment. Credit: projectblue.org

These and other methods (alone or in combination) have allowed for the many discoveries that have been made to take place. But so far, no exoplanets have been directly imaged, which is due to the cancelling effect stars have on optical instruments. Basically, astronomers have been unable to spot the light being reflected off of an exoplanet’s atmosphere because the light coming from the star is up to ten billion times brighter.

The challenge has thus become how to go about blocking this light so that the planets themselves can become visible. One proposed solution to this problem is NASA’s Starshade concept, a giant space structure that would be deployed into orbit alongside a space telescope (most likely, the James Webb Space Telescope). Once in orbit, this structure would deploy its flower-shaped foils to block the glare of distant stars, thus allowing the JWST and other instruments to image exoplanets directly.

But since Alpha Centauri is a binary system (or trinary, if you count Proxima Centauri), being able to directly image any planets around them is even more complicated. To address this, Project Blue has developed plans for a telescope that will be able to suppress light from both Alpha Centauri A and B, while simultaneously taking images of any planets that orbit them. It’s specialized starlight suppression system consists of three components.

First, there is the coronagraph, an instrument which will rely on multiple techniques to block starlight. Second, there’s the deformable mirror, low-order wavefront sensors, and software control algorithms that will manipulate incoming light. Last, there is the post-processing method known as Orbital Differntial Imaging (ODI), which will allow the Project Blue scientist to enhance the contrast of the images taken.

Project Blue’s mission timeline, which woudl commence at the end of the decade and run for six years. Credit: projectblue.org

Given its proximity to Earth, the Alpha Centauri system is the natural choice for conducting such a project. Back in 2012, an exoplanet candidate – Alpha Centauri Bb – was announced. However, in 2015, further analysis indicated that the signal detected was an artefact in the data. In March of 2015, a second possible exoplanet (Alpha Centauri Bc) was announced, but its existence has also come to be questioned.

With an instrument capable of directly imaging this system, the existence of any exoplanets could finally be confirmed (or ruled out). As Franck Marchis – the Senior Planetary Astronomer at the SETI Institute and Project Blue Science Operation Lead – said of the Project:

“Project Blue is an ambitious space mission, designed to answer to a fundamental question, but surprisingly the technology to collect an image of a “Pale Blue Dot” around Alpha Centauri stars is there. The technology that we will use to reach to detect a planet 1 to 10 billion times fainter than its star has been tested extensively in lab, and we are now ready to design a space-telescope with this instrument.”

If Project Blue meets its crowdfunding goals, the organization intends to deploy the telescope into Near-Earth Orbit (NEO) by 2021. The telescope will then spend the next two years observing the Alpha Centauri system with its corongraphic camera. All told, between the development of the instrument and the end of its observation campaign, the mission will last six years, a relatively short run for an astronomical mission.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

However, the potential payoff for this mission would be incredibly profound. By directly imaging another planet in the closest star system to our own, Project Blue could gather vital data that would indicate if any planets there are habitable. For years, astronomers have attempted to learn more about the potential habitability of exoplanets by examining the spectral data produced by light passing through their atmospheres.

However, this process has been limited to massive gas giants that orbit close to their parent stars (i.e. “Super-Jupiters”). While various models have been proposed to place constraints on the atmospheres of rocky planets that orbit within a star’s habitable zone, none have been studied directly. Therefore, if it should prove to be successful, Project Blue would allow for some of the greatest scientific finds in history.

What’s more, it would provide information that could a long way towards informing a future mission to Alpha Centauri, such as Breakthrough Starshot. This proposed mission calls for the use of a large laser array to propel a lightsail-driven nanocraft up to relativistic speeds (20% the speed of light). At this rate, the craft would reach Alpha Centauri within 20 years time and be able to transmit data back using a series of tiny cameras, sensors and antennae.

As the name would suggest, Project Blue hopes to capture the first images of a “Pale Blue Dot” that orbits another star. This is a reference to the photograph of Earth that was taken by the Voyager 1 probe on February 19th, 1990, after the probe concluded its primary mission and was getting ready to leave the Solar System. The photos were taken at the request of famed astronomer and science communicator Carl Sagan.

The “Pale Blue Dot” photograph taken by the Voyager 1 probe. Credit: NASA/JPL

When looking at the photographs, Sagan famously said: “Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.” Thereafter, the name “Pale Blue Dot” came to be synonymous with Earth and capture the sense of awe and wonder that the Voyage 1 photographs evoked.

More recently, other “Pale Blue Dot” photographs have been snapped by missions like the Cassini orbiter. While photographing Saturn and its system of rings in the summer of 2013, Cassini managed to capture images that showed Earth in the background. Given the distance, Earth once again appeared as a small point of light against the darkness of space.

Beyond relying on crowdfunding and the participation of multiple non-profit organizations, this low-cost mission also seeks to capitalize on a growing trend in space exploration, – which is open participation and collaborations between scientific institutions and citizen scientists. This is one of the primary purposes behind Project Blue, which is to engage the public and educate them about the importance of space exploration.

As Jon Morse, the CEO of the BoldlyGo Institute, explained:

“The future of space exploration holds boundless potential for answering profound questions about our existence and destiny. Space-based science is a cornerstone for investigating such questions. Project Blue seeks to engage a global community in a mission to search for habitable planets and life beyond Earth.”

As of the penning of this article, Project Blue has managed to raise $125,561 USD of their goal of $175,000. For those interesting in backing this project, Project Blue’s Indiegogo campaign will remain open for another 11 days. And be sure to check out their promotional video as well:

Further Reading: SETI, Project Blue, Indiegogo

Posted on by Matt Williams

Neptune-Sized Exomoon Found Orbiting a Jupiter-Sized Planet?

Artist's impression of a hypothetical Earth-like moon around a Saturn-like exoplanet. Credit: Wikipedia Commons/ Frizaven

Finding planets beyond our Solar System is already tough, laborious work. But when it comes to confirmed exoplanets, an even more challenging task is determining whether or not these worlds have their own satellites – aka. “exomoons”. Nevertheless, much like the study of exoplanets themselves, the study of exomoons presents some incredible opportunities to learn more about our Universe.

Of all possible candidates, the most recent (and arguably, most likely) one was announced back in July 2017. This moon, known as Kepler-1625 b-i, orbits a gas giant roughly 4,000 light years from Earth. But according to a new study, this exomoon may actually be a Neptune-sized gas giant itself. If true, this will constitute the first instance where a gas giant has been found orbiting another gas giant.

The study, titled “The Nature of the Giant Exomoon Candidate Kepler-1625 b-i“, recently appeared in the scientific journal Astronomy and Astrophysics. The study was conducted by René Heller, an astrophysicist from the Max Planck Institute for Solar System Research, who examined lightcurves obtained by the Kepler mission to place constraints on the exomoon’s mass and determine its true nature.

An artist’s conception of a habitable exomoon orbiting a gas giant. Credit: NASA

Within the Solar System, moons tell us much about their host planet’s formation and evolution. In the same way, the study of exomoons is likely to provide insight into extra-solar planetary systems. As Dr. Heller explained to Universe Today via email, these studies could also shed light on whether or not these systems have habitable planets:

“Moons have proven to be extremely helpful to study the formation and evolution of the planets in the solar system. The Earth’s Moon, for example, was key to set the initial astrophysical conditions, such as the total mass of the Earth and the Earth’s primordial spin state, for what has become our habitable environment. As another example, the Galilean moons around Jupiter have been used to study the conditions of the primordial accretion disk around Jupiter from which the planet pulled its mass 4.5 billion years ago. This accretion disk has long gone, but the moons that formed within the disk are still there. And so we can use the moons, in particular their contemporary composition and water contents, to study planet formation in the far past.”

When it comes to the Kepler-1625 star system, previous studies were able to produce estimates of the radii of both Kepler-1625 b and its possible moon, based on three observed transits it made in front of its star. The light curves produced by these three observed transits are what led to the theory that Kepler-1625 had a Neptune-size exomoon orbiting it, and at a distance of about 20 times the planet’s radius.

But as Dr. Heller indicated in his study, radial velocity measurements of the host star (Kepler-1625) were not considered, which would have produced mass estimates for both bodies. To address this, Dr. Heller considered various mass regimes in addition to the planet and moon’s apparent sizes based on their observed signatures. Beyond that, he also attempted to place the planet and moon into the context of moon formation in the Solar System.

Artist’s impression of an exomoon orbiting a gas giant (left) and a Neptune-sized exoplanet (right). Credit: NASA/JPL-Caltech

The first step, accroding to Dr. Heller, was to conduct estimates of the possible mass of the exomoon candidate and its host planet based on the properties that were shown in the transit lightcurves observed by Kepler.

“A dynamical interpretation of the data suggests that the host planet is a roughly Jupiter-sized (“size” in terms of radius) brown dwarf with a mass of almost 18 Jupiter masses,” he said. “The uncertainties, however, are very large mostly due to the noisiness of the Kepler data and due to the low number of transits (three). In fact, the host object could be a Jupiter-like planet or even be a moderate-sized brown dwarf of up to 37 Jupiter masses. The mass of the moon candidate ranges somewhere between a super-Earth of a few Earth masses and Neptune’s mass.”

Next, Dr. Heller compared the relative mass of the exomoon candidate and Kepler-1625 b and compared this value to various planets and moons of the Solar System. This step was necessary because the moons of the Solar System show two distinct populations, based the mass of the planets compared to their moon-to-planet mass ratios. These comparisons indicate that a moon’s mass is closely related to how it formed.

For instance, moons that formed through impacts – such as Earth’s Moon, and Pluto’s moon Charon – are relatively heavy, whereas moons that formed from a planet’s accretion disk are relatively light. While Jupiter’s moon Ganymede is the most massive moon in the Solar System, it is rather diminutive and tiny compared to Jupiter itself – the largest and most massive body in the Solar System.

Artist’s impression of the view from a hypothetical moon around a exoplanet orbiting a triple star system. Credit: NASA

In the end, the results Dr. Heller obtained proved to be rather interesting. Basically, they indicated that Kepler-1625 b-i cannot be definitively placed in either of these families (heavy, impact moons vs. lighter, accretion moons). As Dr. Heller explained:

“[T]]he most reasonable scenarios suggest that the moon candidate is more of the heavy kind, which suggests it should have formed through an impact. However, this exomoon, if real, is most likely gaseous. The solar system moons are all rocky/icy bodies without a significant gas envelope (Titan has a thick atmosphere but its mass is negligible). So how would a gas giant moon have formed through an impact? I don’t know. I don’t know if anybody knows.

“Alternatively, in a third scenario, Kepler-1625 b-i could have formed through capture, but this implies a very unlikely progenitor planetary binary system, from which it was pulled into a bound orbit around Kepler-1625 b, while its former planetary companion was ejected from the system.”

What was equally interesting were the mass estimates for Keple-1625 b, which Dr. Heller averaged to be 19 Jupiter masses, but could be as high as 112 Jupiter Masses. This means that the host planet could be anything from a gas giant that is just slightly larger than Saturn to a Brown Dwarf or even a Very-Low-Mass-Star (VLMS). So rather than a gas giant moon orbiting a gas giant, we could be dealing with a gas giant moon orbiting a small star, which together orbit a larger star!

An artist’s conception of a T-type brown dwarf. Credit: Tyrogthekreeper/Wikimedia Commons.

It’s the stuff science fiction is made of! And while this study cannot provide exact mass constraints on Keplder-1625 b and its possible moon, its significance cannot be denied. Beyond providing astrophysicists with the first possible example of a gas giant moon, this study is of immense significance as far as the study of exoplanet systems is concerned. If and when Kepler-1625 b-i is confirmed, it will tell us much about the conditions under which its host formed.

In the meantime, more observations are needed to confirm or rule out the existence of this moon. Fortunately, these observations will be taking place in the very near future. When Kepler-1625 b makes it next transit – on October 29th, 2017 – the Hubble Space Telescope will be watching! Based on the light curves it observes coming from the star, scientist should be able to get a better idea of whether or not this mysterious moon is real and what it looks like.

“If the moon turns out to be a ghost in the data, then most of this study would not be applicable to the Kepler-1625 system,” said Dr. Heller. “The paper would nevertheless present an example study of how to classify future exomoons and how to put them into the context of the solar system. Alternatively, if Kepler-1625 b-i turns out to be a genuine exomoon, then my study suggests that we have found a new kind of moon that has a very different formation history than the moons we know as of today. Certainly an exquisite riddle for astrophysicists to solve.”

The study of exoplanet systems is like pealing an onion, albeit in a dark room with the lights turned off. With every successive layer scientists peel back, the more mysteries they find. And with the deployment of next-generation telescopes in the near future, we are bound to learn a great deal more!

Further Reading: Astronomy and Astrophysics

Posted on by Matt Williams

Water Worlds Don’t Stay Wet for Very Long

Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)
Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)

When hunting for potentially habitable exoplanets, one of the most important things astronomers look for is whether or not exoplanet candidates orbit within their star’s habitable zone. This is necessary for liquid water to exist on a planet’s surface, which in turn is a prerequisite for life as we know it. However, in the course of discovering new exoplanets, scientists have become aware of an extreme case known as “water worlds“.

Water worlds are essentially planets that are up to 50% water in mass, resulting in surface oceans that could be hundreds of kilometers deep. According to a new study by a team of astrophysicists from Princeton, the University of Michigan and Harvard, water worlds may not be able to hang on to their water for very long. These findings could be of immense significance when it comes to the hunt for habitable planets in our neck of the cosmos.

This most recent study, titled “The Dehydration of Water Worlds via Atmospheric Losses“, recently appeared in The Astrophysical Journal Letters. Led by Chuanfei Dong from the Department of Astrophysical Sciences at Princeton University, the team conducted computer simulations that took into account what kind of conditions water worlds would be subject to.

Artist’s impression of the planet orbiting a red dwarf star. Credit: ESO/M. Kornmesser

This study was motivated largely by the number of exoplanet discoveries have been made around low-mass, M-type (red dwarf) star systems in recent years. These planets have been found to be comparable in size to Earth – which indicated that they were likely terrestrial (i.e. rocky). In addition, many of these planets – such as Proxima b and three planets within the TRAPPIST-1 system – were found to be orbiting within the stars habitable zones.

However, subsequent studies indicated that Proxima b and other rocky planets orbiting red dwarf stars could in fact be water worlds. This was based on mass estimates obtained by astronomical surveys, and the built-in assumptions that such planets were rocky in nature and did not have massive atmospheres. At the same time, numerous studies have been produced that have cast doubt on whether or not these planets would be able to hold onto their water.

Basically, it all comes down to the type of star and the orbital parameters of the planets. While long-lived, red dwarf stars are known for being variable and unstable compared to our Sun, which results in periodic flares up that would strip a planet’s atmosphere over time. On top of that, planets orbiting within a red dwarf’s habitable zone would likely be tidally-locked, meaning one side of the planet would be constantly exposed to the star’s radiation.

Because of this, scientists are focused on determining just how well exoplanets in different types of star systems could hold onto their atmospheres. As Dr. Dong told Universe Today via email:

“It is fair to say that the presence of an atmosphere is perceived as one of the requirements for the habitability of a planet. Having said that, the concept of habitability is a complex one with myriad factors involved. Thus, an atmosphere by itself will not suffice to guarantee habitability, but it can be regarded as an important ingredient for a planet to be habitable.”

Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech
Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech

To test whether or not a water world would be able to hold onto its atmosphere, the team conducted computer simulations that took into account a variety of possible scenarios. These included the effects of stellar magnetic fields, coronal mass ejections, and atmospheric ionization and ejection for various types of stars – including G-type stars (like our Sun) and M-type stars (like Proxima Centauri and TRAPPIST-1).

With these effects accounted for, Dr. Dong and his colleagues derived a comprehensive model that simulated how long exoplanet atmospheres would last. As he explained it:

“We developed a new multi-fluid magnetohydrodynamic model. The model simulated both the ionosphere and magnetosphere as a whole. Due to the existence of the dipole magnetic field, the stellar wind cannot sweep away the atmosphere directly (like Mars due to the absence of a global dipole magnetic field), instead, the atmospheric ion loss was caused by the polar wind.

“The electrons are less massive than their parent ions, and as a result, are more easily accelerated up to and beyond the escape velocity of the planet. This charge separation between the escaping, low-mass electrons and significantly heavier, positively-charged ions sets up a polarization electric field. That electric field, in turn, acts to pull the positively charged ions along behind the escaping electrons, out of the atmosphere in the polar caps.”

Artist’s impression of the view from the most distant exoplanet discovered around the red dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser.

What they found was that their computer simulations were consistent with the current Earth-Sun system. However, in some extreme possibilities – such as exoplanets around M-type stars – the situation is very different and the escape rates could be one thousand times greater or more. The result means that even a water world, if it orbits an red dwarf star, could lose its atmosphere after about a gigayear (Gyr), one billion years.

Considering that life as we know it took around 4.5 billion years to evolve, one billion years is a relatively brief window. In fact, as Dr. Dong explained, these results indicate that planets that orbit M-type stars would be hard pressed to develop life:

“Our results indicate that the ocean planets (orbiting a Sun-like star) will retain their atmospheres much longer than the Gyr timescale as the ion escape rates are far too low, therefore, it allows a longer duration for life to originate on these planets and evolve in terms of complexity. In contrast, for exoplanets orbiting M-dwarfs, they could have their oceans depleted over the Gyr timescale due to the more intense particle and radiation environments that exoplanets experience in close-in habitable zones. If the atmosphere were to be depleted over the timescale less than Gyr, this could prove to be problematic for the origin of life (abiogenesis) on the planet.”

Once again, these results cast doubt on the potential habitability of red dwarf star systems. In the past, researchers have indicated that the longevity of red dwarf stars, which can remain in their main sequence for up to 10 trillion years or longer, make them the best candidate for finding habitable exoplanets. However, the stability of these stars and the way in which they are likely to strip planets of their atmospheres seems to indicate otherwise.

An artist’s depiction of planets transiting a red dwarf star in the TRAPPIST-1 System. Credit: NASA/ESA/STScl

Studies such as this one are therefore highly significant in that they help to address just how long a potentially habitable planet around a red dwarf star could remain potentially habitable. As Dr. Dong indicated:

“Given the importance of atmospheric loss on planetary habitability, there has been a great deal of interest in using telescopes such as the upcoming James Webb Space Telescope (JWST) to determine whether these planets have atmospheres and, if so, what their composition are like. It is expected that the JWST should be capable of characterizing these atmospheres (if present), but quantifying the escape rates accurately requires a much higher degree of precision and may not be feasible in the near-future.”

The study is also significant as far as our understanding of the Solar System and its evolution is concerned. At one time, scientists have ventured that both Earth and Venus may have been water worlds. How they made the transition from being very watery to what they are today – in the case of Venus, dry and hellish; and in the case of Earth, having multiple continents – is an all-important question.

In the future, more detailed surveys are anticipated that could help shed light on these competing theories. When the James Webb Space Telescope (JWST) is deployed in Spring of 2018, it will use its powerful infrared capabilities to study planets around nearby red dwarfs, Proxima b being one of them. What we learn about this and other distant exoplanets will go a long way towards informing our understanding of how our own Solar System evolved as well.

Further Reading: CfA, The Astrophysical Journal Letters

Posted on by Matt Williams

Looking for Signs of Life on Distant Planets Just Got Easier

This illustration shows a star's light illuminating the atmosphere of a planet. Credits: NASA Goddard Space Flight Center

When it comes to searching for worlds that could support extra-terrestrial life, scientists currently rely on the “low-hanging fruit” approach. Since we only know of one set of conditions under which life can thrive – i.e. what we have here on Earth – it makes sense to look for worlds that have these same conditions. These include being located within a star’s habitable zone, having a stable atmosphere, and being able to maintain liquid water on the surface.

Until now, scientists have relied on methods that make it very difficult to detect water vapor in the atmosphere’s of terrestrial planets. But thanks to a new study led by Yuka Fujii of NASA’s Goddard Institute for Space Studies (GISS), that may be about to change. Using a new three-dimensional model that takes into account global circulation patterns, this study also indicates that habitable exoplanets may be more common than we thought.

The study, titled “NIR-driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets“, recently appeared in The Astrophysical Journal. In addition to Dr. Fujii, who is also a member of the Earth-Life Science Institute at the Tokyo Institute of Technology, the research team included Anthony D. Del Genio (GISS) and David S. Amundsen (GISS and Columbia University).

Artist’s concept of the hot Jupiter WASP-121b, which presents the best evidence yet of a stratosphere on an exoplanet – generated using Engine House VFX. Credit: Bristol Science Centre/University of Exeter

To put it simply, liquid water is essential to life as we know it. If a planet does not have a warm enough atmosphere to maintain liquid water on its surface for a sufficient amount of time (on the order of billions of years), then it is unlikely that life will be able to emerge and evolve. If a planet is too distant from its star, its surface water will freeze; if it is too close, its surface water will evaporate and be lost to space.

While water has been detected in the atmospheres of exoplanets before, in all cases, the planets were massive gas giants that orbited very closely to their stars. (aka. “Hot Jupiters”). As Fujii and her colleagues state in their study:

“Although H2O signatures have been detected in the atmospheres of hot Jupiters, detecting molecular signatures, including H2O, on temperate terrestrial planets is exceedingly challenging, because of the small planetary radius and the small scale height (due to the lower temperature and presumably larger mean molecular weight).”

When it comes to terrestrial (i.e. rocky) exoplanets, previous studies were forced to rely on one-dimensional models to calculate the presence of water. This consisted of measuring hydrogen loss, where water vapor in the stratosphere is broken down into hydrogen and oxygen from exposure to ultraviolet radiation. By measuring the rate at which hydrogen is lost to space, scientists would estimate the amount of liquid water still present on the surface.

Artist’s impression of the “Venus-like” exoplanet GJ 1132b. Credit: cfa.harvard.edu

However, as Dr. Fujii and her colleagues explain, such models rely on several assumptions that cannot be addressed, which include the global transport of heat and water vapor vapor, as well as the effects of clouds. Basically, previous models predicted that for water vapor to reach the stratosphere, long-term surface temperatures on these exoplanets would have to be more than 66 °C (150 °F) higher than what we experience here on Earth.

These temperatures could create powerful convective storms on the surface. However, these storms could not be the reason water reaches the stratosphere when it comes to slowly rotating planets entering a moist greenhouse state – where water vapor intensifies heat. Planets that orbit closely to their parent stars are known to either have a slow rotation or to be tidally-locked with their planets, thus making convective storms unlikely.

This occurs quite often for terrestrial planets that are located around low-mass, ultra cool, M-type (red dwarf) stars. For these planets, their proximity to their host star means that it’s gravitational influence will be strong enough to slow down or completely arrest their rotation. When this occurs, thick clouds form on the dayside of the planet, protecting it from much of the star’s light.

The team found that, while this could keep the dayside cool and prevent water vapor from rising, the amount of near-Infrared radiation (NIR) could provide enough heat to cause a planet to enter a moist greenhouse state. This is especially true of M-type and other cool dwarf stars, which are known to produce more in the way of NIR. As this radiation warms the clouds, water vapor will rise into the stratosphere.

Artist’s impression of Proxima b, the closest exoplanet to the Solar System. In the background, the binary system of Alpha Centauri can be seen. Credit: ESO/M. Kornmesser

To address this, Fujii and her team relied on three-dimensional general circulation models (GCMs) which incorporate atmospheric circulation and climate heterogeneity. For the sake of their model, the team started with a planet that had an Earth-like atmosphere and was entirely covered by oceans. This allowed the team to clearly see how variations in distance from different types of stars would effect conditions on the planets surfaces.

These assumptions allowed the team to clearly see how changing the orbital distance and type of stellar radiation affected the amount of water vapor in the stratosphere. As Dr. Fujii explained in a NASA press release:

“Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study… We found an important role for the type of radiation a star emits and the effect it has on the atmospheric circulation of an exoplanet in making the moist greenhouse state.”

In the end, the team’s new model demonstrated that since low-mass star emit the bulk of their light at NIR wavelengths, a moist greenhouse state will result for planets orbiting closely to them. This would result in conditions on their surfaces that comparable to what Earth experiences in the tropics, where conditions are hot and moist, instead of hot and dry.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO

What’s more, their model indicated that NIR-driven processes increased moisture in the stratosphere gradually, to the point that exoplanets orbiting closer to their stars could remain habitable. This new approach to assessing potential habitability will allow astronomers to simulate circulation of planetary atmospheres and the special features of that circulation, which is something one-dimensional models cannot do.

In the future, the team plans to assess how variations in planetary characteristics -such as gravity, size, atmospheric composition, and surface pressure – could affect water vapor circulation and habitability. This will, along with their 3-dimensional model that takes planetary circulation patterns into account, allow astronomers to determine the potential habitability of distant planets with greater accuracy. As Anthony Del Genio indicated:

“As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state. Current technology will be pushed to the limit to detect small amounts of water vapor in an exoplanet’s atmosphere. If there is enough water to be detected, it probably means that planet is in the moist greenhouse state.”

Beyond offering astronomers a more comprehensive method for determining exoplanet habitability, this study is also good news for exoplanet-hunters hoping to find habitable planets around M-type stars. Low-mass, ultra-cool, M-type stars are the most common star in the Universe, accounting for roughly 75% of all stars in the Milky Way. Knowing that they could support habitable exoplanets greatly increases the odds of find one.

Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech
Illustration showing the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Credits: NASA/JPL-Caltech

In addition, this study is VERY good news given the recent spate of research that has cast serious doubt on the ability of M-type stars to host habitable planets. This research was conducted in response to the many terrestrial planets that have been discovered around nearby red dwarfs in recent years. What they revealed was that, in general, red dwarf stars experience too much flare and could strip their respective planets of their atmospheres.

These include the 7-planet TRAPPIST-1 system (three of which are located in the star’s habitable zone) and the closest exoplanet to the Solar System, Proxima b. The sheer number of Earth-like planets discovered around M-type stars, coupled with this class of star’s natural longevity, has led many in the astrophysical community to venture that red dwarf stars might be the most likely place to find habitable exoplanets.

With this latest study, which indicates that these planets could be habitable after all, it would seem that the ball is effectively back in their court!

Further Reading: NASA, The Astrophysical Journal

 

Posted on by Matt Williams

Debris Disks Around Stars Could Point the Way to Giant Exoplanets

This artist's rendering shows a large exoplanet causing small bodies to collide in a disk of dust. Credit: NASA/JPL-Caltech

According to current estimates, there could be as many as 100 billion planets in the Milky Way Galaxy alone. Unfortunately, finding evidence of these planets is tough, time-consuming work. For the most part, astronomers are forced to rely on indirect methods that measure dips in a star’s brightness (the Transit Method) of Doppler measurements of the star’s own motion (the Radial Velocity Method).

Direct imaging is very difficult because of the cancelling effect stars have, where their brightness makes it difficult to spot planets orbiting them. Luckily a new study led by the Infrared Processing and Analysis Center (IPAC) at Caltech has determined that there may be a shortcut to finding exoplanets using direct imaging. The solution, they claim, is to look for systems with a circumstellar debris disk, for they are sure to have at least one giant planet.

The study, titled “A Direct Imaging Survey of Spitzer Detected Debris Disks: Occurrence of Giant Planets in Dusty Systems“, recently appeared in The Astronomical Journal. Tiffany Meshkat, an assistant research scientist at IPAC/Caltech, was the lead author on the study, which she performed while working at NASA’s Jet Propulsion Laboratory as a postdoctoral researcher.

A circumstellar disk of debris around a mature stellar system could indicate the presence of Earth-like planets. Credit: NASA/JPL
Artist’s impression of circumstellar disk of debris around a distant star. Credit: NASA/JPL

For the sake of this study, Dr. Meshkat and her colleagues examined data on 130 different single-star systems with debris disks, which they then compared to 277 stars that do not appear to host disks. These stars were all observed by NASA’s Spitzer Space Telescope and were all relatively young in age (less than 1 billion years). Of these 130 systems, 100 had previously been studied for the sake of finding exoplanets.

Dr. Meshkat and her team then followed up on the remaining 30 systems using data from the W.M. Keck Observatory in Hawaii and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile. While they did not detect any new planets in these systems, their examinations helped characterize the abundance of planets in systems that had disks.

What they found was that young stars with debris disks are more likely to also have giant exoplanets with wide orbits than those that do not. These planets were also likely to have five times the mass of Jupiter, thus making them “Super-Jupiters”. As Dr. Meshkat explained in a recent NASA press release, this study will be of assistance when it comes time for exoplanet-hunters to select their targets:

“Our research is important for how future missions will plan which stars to observe. Many planets that have been found through direct imaging have been in systems that had debris disks, and now we know the dust could be indicators of undiscovered worlds.”

This artist’s conception shows how collisions between planetesimals can create additional debris. Credit: NASA/JPL-Caltech

This study, which was the largest examination of stars with dusty debris disks, also provided the best evidence to date that giant planets are responsible for keeping debris disks in check. While the research did not directly resolve why the presence of a giant planet would cause debris disks to form, the authors indicate that their results are consistent with predictions that debris disks are the products of giant planets stirring up and causing dust collisions.

In other words, they believe that the gravity of a giant planet would cause planestimals to collide, thus preventing them from forming additional planets. As study co-author Dimitri Mawet, who is also a JPL senior research scientist, explained:

“It’s possible we don’t find small planets in these systems because, early on, these massive bodies destroyed the building blocks of rocky planets, sending them smashing into each other at high speeds instead of gently combining.”

Within the Solar System, the giant planets create debris belts of sorts. For example, between Mars and Jupiter, you have the Main Asteroid Belt, while beyond Neptune lies the Kuiper Belt. Many of the systems examined in this study also have two belts, though they are significantly younger than the Solar System’s own belts – roughly 1 billion years old compared to 4.5 billion years old.

Artist’s impression of Beta Pictoris b. Credit: ESO L. Calçada/N. Risinger (skysurvey.org)

One of the systems examined in the study was Beta Pictoris, a system that has a debris disk, comets, and one confirmed exoplanet. This planet, designated Beta Pictoris b, which has 7 Jupiter masses and orbits the star at a distance of 9 AUs – i.e. nine times the distance between the Earth and the Sun. This system has been directly imaged by astronomers in the past using ground-based telescopes.

Interestingly enough, astronomers predicted the existence of this exoplanet well before it was confirmed, based on the presence and structure of the system’s debris disk. Another system that was studied was HR8799, a system with a debris disk that has two prominent dust belts. In these sorts of systems, the presence of more giant planets is inferred based on the need for these dust belts to be maintained.

This is believed to be case for our own Solar System, where 4 billion years ago, the giant planets diverted passing comets towards the Sun. This resulted in the Late Heavy Bombardment, where the inner planets were subject to countless impacts that are still visible today. Scientists also believe that it was during this period that the migrations of Jupiter, Saturn, Uranus and Neptune deflected dust and small bodies to form the Kuiper Belt and Asteroid Belt.

Dr. Meshkat and her team also noted that the systems they examined contained much more dust than our Solar System, which could be attributable to their differences in age. In the case of systems that are around 1 billion years old, the increased presence of dust could be the result of small bodies that have not yet formed larger bodies colliding. From this, it can be inferred that our Solar System was once much dustier as well.

Artist’s concept of the multi-planet system around HR 8799, initially discovered with Gemini North adaptive optics images. Credit: Gemini Observatory/Lynette Cook”

However, the authors note is also possible that the systems they observed – which have one giant planet and a debris disk – may contain more planets that simply have not been discovered yet. In the end, they concede that more data is needed before these results can be considered conclusive. But in the meantime, this study could serve as an guide as to where exoplanets might be found.

As Karl Stapelfeldt, the chief scientist of NASA’s Exoplanet Exploration Program Office and a co-author on the study, stated:

“By showing astronomers where future missions such as NASA’s James Webb Space Telescope have their best chance to find giant exoplanets, this research paves the way to future discoveries.”

In addition, this study could help inform our own understanding of how the Solar System evolved over the course of billions of years. For some time, astronomers have been debating whether or not planets like Jupiter migrated to their current positions, and how this affected the Solar System’s evolution. And there continues to be debate about how the Main Belt formed (i.e. empty of full).

Last, but not least, it could inform future surveys, letting astronomers know which star systems are developing along the same lines as our own did, billions of years ago. Wherever star systems have debris disks, they an infer the presence of a particularly massive gas giant. And where they have a disk with two prominent dust belts, they can infer that it too will become a system containing many planets and and two belts.

Further Reading: NASA, The Astrophysical Journal

Posted on by Matt Williams

Hubble Spots Pitch Black Hot Jupiter that “Eats Light”

Illustration showing one of the darkest known exoplanets - a hot Jupiter as black as fresh asphalt - orbiting a star like our Sun. The day side of the planet, called WASP-12b, eats light rather than reflects it into space. Something is pulling this planet into its star. Credit: NASA, ESA, and G. Bacon (STScI)
Illustration showing one of the darkest known exoplanets - a hot Jupiter as black as fresh asphalt - orbiting a star like our Sun. The day side of the planet, called WASP-12b, eats light rather than reflects it into space. Something is pulling this planet into its star. Credit: NASA, ESA, and G. Bacon (STScI)

The study of extra-solar planets has revealed discoveries that have confounded expectations and boggled the mind! Whether it’s Super-Earths that become diamond planets, multiple rocky planets orbiting closely together, or “Hot Jupiters” with traces of gaseous metal in their atmospheres, there’s been no shortage of planets out there for which there is no comparison here in the Solar System.

In this respect, WASP-12b is in good company. This Hot-Jupiter, located in a star system 1400 light years from Earth in the direction of the Auriga constellation, was recently studied by a team of astronomers using the Hubble Space Telescope. Due to the particular nature of its atmosphere, which absorbs the vast majority of light it receives instead of reflecting it, this planet appeared pitch black when observed by the Hubble team.

The study which details their findings, “The Very Low Albedo of WASP-12b from Spectral Eclipse Observations with Hubble“, was recently published in The Astrophysical Journal. Led by Taylor Bell, a researcher at the Institute for Research on Exoplanets (IREx) at McGill University, the team consulted data from the Hubble’s Space Telescope Imaging Spectrograph (STIS) to observe WASP-12b during an optical eclipse.

WASP-12b orbits so close to its star that it is heated to a record-breaking 2500°C. Credit: ESA/C Carreau

Like all Hot Jupiters, WASP-12b is similar in mass to Jupiter (1.35 to 1.43 Jupiter masses) and orbits very close to its star. At a distance of just 3.4 million km (2.115 million mi), or 0.0229 AU, it takes a little over a day to complete a single orbit. Because of its proximity, one side of the planet is constantly facing towards it’s sun – i.e. it is tidally locked with its star.

Because of its orbit, temperatures on the day side of the planet are estimated to reach as high as 2811 K (2538 °C; 4600 °F). It is because of these extreme temperatures that most molecules are unable to survive on the day side of the planet, so clouds cannot form to reflect light back into space. As a result, most incoming light penetrates deep into the planet’s atmosphere, where it is absorbed by hydrogen atoms and converted into heat energy.

This was what Bell and his team noticed as they observed the planet passing behind its star (aka. an optical eclipse). Using the STIS, they monitored the system for any dips in starlight, which would indicate how much reflected light was being given off by the planet. However, their observations did not detect reflected light, which indicated that the sun-facing side was absorbing most of the light it was receiving.

As Bell explained in a NASA press statement, this was quite the unusual find: “We did not expect to find such a dark exoplanet,” he said. “Most hot Jupiters reflect about 40 percent of starlight.” However, observations conducted of the night side of the planet show that things are quite different there. On this side, temperatures are about 1366 K (1093 °C; 2000 °F) cooler, which allows water vapor and clouds to form.

An artist’s impression of WASP 12-b being slowly consumed as a result of its ridiculously tight orbit around its star. Credit: NASA.

Back in 2013, scientists working with the HST detected traces of water vapor in the atmosphere (and possible traces of clouds as well) while studying the day/night boundary. As Bell indicated, this new research just goes to show just how diverse this type of gas giant can be:

“This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters. You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they’re both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don’t keep up the pace.”

Since its discovery in 2008, several telescopes have studied WASP-12b, including Hubble, NASA’s Spitzer Space Telescope, and NASA’s Chandra X-ray Observatory. Previous observations by Hubble’s Cosmic Origins Spectrograph (COS) also revealed that the planet may be losing size and mass due to super-heated material from its atmosphere slowly being accreted onto the star.

This is just the latest find in a slew that has confounded scientists expectations about exoplanets. The more we come to learn about the nature and diversity of these distant worlds, the more tantalizing they seem and the more appealing the prospect of exploring them directly someday becomes!

Further Reading: NASA, IREx, Astrophysical Journal Letters

Posted on by Matt Williams

Astronomers Spot Hellish World with Titanium in its Atmosphere

Artist's impression showing the exoplanet WASP-19b, in which atmosphere astronomers detected titanium oxide for the first time. Credit: ESO

The hunt for exoplanets has turned up many fascinating case studies. For example, surveys have turned up many “Hot Jupiters”, gas giants that are similar in size to Jupiter but orbit very close to their suns. This particular type of exoplanet has been a source of interest to astronomers, mainly because their existence challenges conventional thinking about where gas giants can exist in a star system.

Hence why an international team led by researchers from the European Southern Observatory (ESO) used the Very Large Telescope (VLT) to get a better look at WASP-19b, a Hot Jupiter located 815 light-years from Earth. In the course of these observations, they noticed that the planet’s atmosphere contained traces of titanium oxide, making this the first time that this compound has been detected in the atmosphere of a gas giant.

The study which describes their findings, titled “Detection of titanium oxide in the atmosphere of a hot Jupiter“, recently appeared in the science journal Nature. Led by Elyar Sedaghati – a recent graduate from the Technical University of Berlin and a fellow at the European Southern Observatory – the team used data collected by the VLT array over the course of a year to study WASP-19b.

Like all Hot Jupiters, WASP-19b has about the same mass as Jupiter and orbits very close to its sun. In fact, its orbital period is so short  – just 19 hours – that temperatures in its atmosphere are estimated to reach as high as 2273 K (2000 °C; 3632 °F). That’s over four times as hot as Venus, where temperatures are hot enough to melt lead! In fact, temperatures on WASP-19b are hot enough to melt silicate minerals and platinum!

The study relied on the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument on the VLT, a multi-mode optical instrument capable of conducting imaging, spectroscopy and the study of polarized light (polarimetry). Using FORS2, the team observing the planet as it passed in front of its star (aka. made a transit), which revealed valuable spectra from its atmosphere.

After carefully analyzing the light that passed through its hazy clouds, the team was surprised to find trace amounts of titanium oxide (as well as sodium and water). As Elyar Sedaghati, who spent 2 years as a student with the ESO to work on this project, said of the discovery in an ES press release:

“Detecting such molecules is, however, no simple feat. Not only do we need data of exceptional quality, but we also need to perform a sophisticated analysis. We used an algorithm that explores many millions of spectra spanning a wide range of chemical compositions, temperatures, and cloud or haze properties in order to draw our conclusions.”

Titanium oxide is a very rare compound which is known to exist in the atmospheres of cool stars. In small quantities, it acts as a heat absorber, and is therefore likely to be partly responsible for WASP-19b experiencing such high temperatures. In large enough quantities, it can prevent heat from entering or escaping an atmosphere, causing what is known as thermal inversion.

This is a phenomena where temperatures are higher in the upper atmosphere and lower further down. On Earth, ozone plays a similar role, causing an inversion of temperatures in the stratosphere. But on gas giants, this is the opposite of what usually happens. Whereas Jupiter, Saturn, Uranus and Neptune experience colder temperatures in their upper atmospheres, temperatures are much hotter closer to the core due to increases in pressure.

The team believes that the presence of this compound could have a substantial effect on the atmosphere’s temperature, structure and circulation. What’s more, the fact that the team was able to detect this compound (a first for exoplanet researchers) is an indication of how exoplanet studies are achieving new levels of detail. All of this is likely to have a profound impact on future studies of exoplanet atmospheres.

The study would also have not been possible were it not for the FORS2 instrument, which was added to the VLT array in recent years. As Henri Boffin, the instrument scientist who led the refurbishment project, commented:

“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose. Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”

Looking ahead, it is clear that the detection of metal oxides and other similar substances in exoplanet atmospheres will also allow for the creation of better atmospheric models. With these in hand, astronomers will be able to conduct far more detailed and accurate studies on exoplanet atmospheres, which will allow them to gauge with greater certainty whether or not any of them are habitable.

So while this latest planet has no chance of supporting life – you’d have better luck finding ice cubes in the Gobi desert! – its discovery could help point the way towards habitable exoplanets in the future. On step closer to finding a world that could support life, or possibly that elusive Earth 2.0!

Further Reading: ESO, Nature

Posted on by Matt Williams

Three Possible Super-Earths Discovered Around Nearby Sun-Like Star

Artist’s impression of a Super-Earth planet orbiting a Sun-like star. Credit: ESO/M. Kornmesser

Since it was launched in 2009, NASA’s Kepler mission has continued to make important exoplanet discoveries. Even after the failure of two reaction wheels, the space observatory has found new life in the form of its K2 mission. All told, this space observatory has detected 5,017 candidates and confirmed the existence of 2,494 exoplanets using the Transit Method during its past eight years in service.

The most recent discovery was made by an international team of astronomers around Gliese 9827 (GJ 9827), a late K-type dwarf star located about 100 light-years from Earth. Using data provided by the K2 mission, they detected the presence of three Super-Earths. This star system is the closest exoplanet-hosting star discovered by K2 to date, which makes these planets well-suited for follow-up studies.

The study which describes their findings, titled “A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at Thirty Parsecs“, was recently published online. Led by Dr. Jospeh E. Rodriguez from the Harvard-Smithsonian Center for Astrophysics (CfA), the team includes researchers from the University of Austin, the Massachusetts Institute of Technology (MIT), and the NASA Exoplanet Science Institute (NExSci) at Caltech.

The Transit Method, which remains one of the most trusted means for exoplanet detection, consists of monitoring stars for periodic dips in brightness. These dips correspond to planets passing (aka. transiting) in front of the star causing a measurable drop in the light coming from it. This method also offers unique opportunities to examine light passing through an exoplanet’s atmosphere. As Dr. Rodriguez told Universe Today via email:

“The success of Kepler combined with ground based radial velocity and transit surveys has now led to the discovery of over 4000 planetary system. Since we now know that planets appear to be quite common, the field has shifted its focus to understand architectures, interior structures, and atmospheres. These key properties of planetary systems help us understand some fundamental questions: how do planets form and evolve? What are the terrestrial planets around other stars like, are they similar to Earth in composition and atmosphere?”

These questions were central to the team’s study, which relied on data obtained during Campaign 12 of the K2 mission – from December 2016 to March 2017. After consulting this data, the team noted the presence of three super-Earth sized planets orbiting in a very compact configuration. This system, as they note in their study, was independently and simultaneously discovered by another team from Wesleyan University.

These three planetary objects, designated as GJ 9827 b, c, and d, are located at a distance of about 0.02, 0.04 and 0.06 AU from their host star (respectively). Owing to their sizes and radii, these planets are classified as “Super-Earths”, and have radii of 1.6, 1.2, and 2.1 times the radius of Earth. They are also located very close to their host star, completing orbits within 6.2 days.

The light curve obtained during Campaign 12 of the K2 mission of the GJ 9827 system. Credit: Rodriguez et al., 2017

Specifically, GJ 9827 b measures 1.64 Earth radii, has a mass of up to 4.25 Earth masses, a 1.2 day orbital period, and a temperature of 1,119 K (846 °C; 1555 °F). Meanwhile, GJ 9827 c measures 1.29 Earth radii, has a mass of 2.62 Earth masses, an orbital period of 3.6 days, and a temperature of 774 K (500 °C; 934°F). Lastly, GJ 9827 d measures 2.08 Earth radii, has a mass of 5.3 Earth masses, a 6.2 day period, and a temperature of 648 K (375 °C; 707 °F).

In short, all three planets are very hot, with temperatures that are hot as Venus and Mercury or (in the case of GJ 9827b) is even hotter! Interestingly, these radii and mass estimates place these planets within the transition boundary between terrestrial (i.e. rocky) planets and gas giants. In fact, the team found that GJ 9827 b and c fall in or close to the known gap in radius distribution for planets that are in between these two populations.

In other words, these planets could be rocky or gaseous, and the team won’t know for sure until they can place more accurate constraints on their masses. What’s more, none of these planets are likely to be capable of supporting life, certainly not as we know it! So if you were hoping that this latest find would produce an Earth-analog or potentially habitable planet, you’re sadly mistaken.

Nevertheless, the fact that these planets straddle the radius and mass boundary between terrestrial and gaseous planets – and the fact that this system is the closest planetary system to be identified by the K2 mission – makes the system well-situated for studies designed to probe the interior structure and atmosphere of exoplanets.

Artistic design of the super-Earth orbiting a Sun-like star. Credit: Gabriel Pérez/SMM (IAC)

The reason for this has much to do with the brightness of the host star. In addition to being relatively close to our Sun (~100 light-years), this K-type star is very bright and also relatively small – about 60% the size of our Sun. As a result, any planet passing in front of it would be able to block out more light than if the star were larger. But as noted, there’s also the curious nature of the planets themselves. As Dr. Rodriguez indicated:

“Recently, we have found planets around other stars that have no analogue to a planet in our own system. These are known as “super Earths” and they have radii of 1-3 times the radius of the Earth. To add to the complexity of these planets, their is a clear dichotomy in their composition within this radius range. The larger super Earths (>1.6 x radius of the Earth) appear to be less dense, consistent with a puffy Hydrogen/Helium atmosphere. However, the smaller super Earths are more dense, consistent with an Earth-like composition (rock).

“As mentioned above, the GJ 9827 system hosts three super Earth sized planets. Interestingly, planet c has a radius consistent with it being rocky, planet d is consistent with being puffy, and planet b has a radius that is right on what we believe to be the transition boundary between rock and gas. Therefore, by studying the atmospheres of super-Earths, we may better understand the transition from dense rocky planets to puffier planets with very thick atmospheres (like Neptune).”

Artist’s impression of the super-Earth orbiting closely to its parent star. Credit: ESA/NASA

Looking ahead, the team hopes to conduct further studies to determine the masses of these planets more precisely. From this, they will be able to place better constraints on their compositions and determine if they are Super-Earths, mini gas giants, or some of each. Beyond that, they are to conduct more detailed studies of this system with next-generation instruments like the James Webb Space Telescope (JWST), which is scheduled to launch in 2018.

“I am really interested in studying the atmosphere of GJ 9827 b, whether it is rocky or puffy,” said Dr. Rodriguez. “This planet has a radius at the rock/gas transition but it is very close to its host star. Therefore, by studying the chemical composition of its atmosphere we may better understand the impact of the host star’s proximity has on the evolution of its atmosphere.  To do this we would use JWST to take spectroscopic observations during the transit of GJ 9827b (known as “Transmission Spectroscopy”). From this observations we will gather information on the chemical composition and extent of the planet’s atmosphere.“

Now that we have thousands of extra-solar planet discoveries under our belt, its only natural that research would be shifting towards trying to understand these planets better. In the coming years and decades, we are likely to learn volumes about the respective structures, compositions, atmospheres, and surface features of many distant worlds. One can only imagine what kind of things these studies will turn up!

Further Reading: arXiv