Upcoming Telescopes Should be Able to Detect Mountains and Other Landscapes on Extrasolar Planets

The study of exoplanets has advanced by leaps and bounds in the past few decades. Between ground-based observatories and spacecraft like the Kepler mission, a total of 3,726 exoplanets have been confirmed in 2,792 systems, with 622 systems having more than one planet (as of Jan. 1st, 2018). And in the coming years, scientists expect that many more discoveries will be possible thanks to the deployment of next-generation missions.

These include NASA’s James Webb Space Telescope (JWST) and several next-generation ground based observatories. With their advanced instruments, these and other observatories are not only expected to find many more exoplanets, but to reveal new and fascinating things about them. For instance, a recent study from Columbia University indicated that it will be possible, using the Transit Method, to study surface elevations on exoplanets.

The study, which recently appeared online under the title “Finding Mountains with Molehills: The Detectability of Exotopography“, was conducted by Moiya McTier and David Kipping – and graduate student and an Assistant Professor of Astronomy at Columbia University, respectively. Based on models they created using bodies in our Solar System, the team considered whether transit surveys might be able to reveal topographical data on exoplanets.

Artist’s impression of an extra-solar planet transiting its star. Credit: QUB Astrophysics Research Center

To recap, the Transit Method (aka. Transit Photometry) is currently the most popular and reliable means for detecting exoplanets. It consists of astronomers measuring the light curve of distant stars over time and looking for periodic dips in brightness. These dips are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.

By measuring the rate at which the star’s light dips, and the period with which the dimming occurs, astronomer are not only able to determine the presence of exoplanets, but also place accurate constraints on their size and orbital periods. According to McTier and Kipping, this same method could also reveal the presence of geographical features – for instance, mountain ranges, volcanoes, trenches, and craters.

As they indicate in their study, in lieu of direct imaging, indirect methods are the only means astronomers have for revealing data on an exoplanet’s surface. Unfortunately, there is no conceivable way that the radial velocity, microlensing, astrometry, and timing methods could reveal exotopography. This leaves the transit method, which has some potential in this respect. As they state:

“The transit method directly measures the sky-projected area of a planet’s silhouette relative to that of a star, under the assumption that the planet is not luminous itself… This fact implies that there is indeed some potential for transits to reveal surface features, since the planet’s silhouette is certainly distorted from a circular profile due to the presence of topography.”

Satellite image of the Himalayan mountain chain, as imaged by NASA’sLandsat-7 imagery of Himalayas. Credit: NASA

In other words, as a planet transits in front of its host star, the light passing around the planet itself could be measured for small variations. These could indicate the presence of mountain ranges and other large-scale features like massive chasms. To test this theory, they considered planets in the Solar System as templates for how the scattering of light during a transit could reveal large-scale features.

As an example, they consider what an Earth analog planet would reveal if the Himalayan mountain range ran from north to south and was wide enough to span 1° in longitude:

“Now assume that the planet completes half of one rotation as it transits its parent star from our point of view, which is all that is necessary to see all of the planet’s features appear on its silhouette without repeating. As our hypothetical planet rotates and the Himalayan block moves into and out of view, the change in silhouette will result in different transit depths…”

Ultimately, they consider that Mars would be the ideal test case due to its combination of small size, low surface gravity, and active internal volcanism, which has caused it become what they describe as the “bumpiest body in the Solar System”. When paired with a white dwarf star, this presents the optimal case for using light curves to determine exotopography.

Color Mosaic of Olympus Mons on Mars
Color mosaic of Mars’ greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL

At a distance of about 0.01 AU (which would be within a white dwarf’s habitable zone), they calculate that a Mars-sized planet would have an orbital period of 11.3 hours. This would allow for many transits to be observed in a relatively short viewing period, thus ensuring a greater degree of accuracy. At the same time, the team admits that their proposed methods suffers from drawbacks.

For instance, due to the presence of astrophysical and instrumental noise, they determined that their method would be unproductive when it comes to studying exoplanets around Sun-like stars and M-type (red dwarf) stars. But for Mars-like planets orbiting low mass, white dwarf stars, the method could produce some highly valuable scientific returns.

While this might sound rather limited, it would present some rather fascinating opportunities to learn more about planets beyond our Solar System. As they explain:

“Finding the first evidence of mountains on planets outside our solar system would be exciting in its own right, but we can also infer planet characteristics from the presence and distribution of surface features. For example, a detection of bumpiness could lead to constraints on a planet’s internal processes.”

In short, planets with a high degree of bumpiness would indicate tectonic activity or the buildup of lava caused by internal heating sources. Those with the highest bumpiness (i.e. like Mars) would indicate that they too experience a combination internal processes, low surface gravity, volcanism, and a lack of tectonic plate movement. Meanwhile, low-bumpiness planets are less likely to have any of these internal processes and their surfaces are more likely to be shaped by external factors – like asteroid bombardment.

Artist’s impression of the OWL Telescope being deployed at night from its enclosure, where it will operated during the daytime. Credit: ESO

Based on their estimates, they conclude that the various super telescopes that are scheduled to be commissioned in the coming years would be up to task. These include the ESO’s OverWhelmingly Large (OWL) Telescope, a 100-meter proposed optical and near-infrared telescope that would build on the success of the Very Large Telescope (VLT) and the upcoming Extremely Large Telescope (ELT).

Another example is the Colossus Telescope, a 74-meter optical and infrared telescope that is currently being commissioned by an international consortium. Once operational, it will be the largest telescope optimized for detecting extrasolar life and extraterrestrial civilizations.

In the past, the success of exoplanet hunters has come down to a combination of factors. In addition to greater levels of cooperation between institutions, amateur astronomers and citizen scientists, there has also been the way in which improved technology has coincided with new theoretical models. As more data become available, scientists are able to produce more educated estimates on what we might be able to learn once new instruments come online.

When the next-generation telescopes take to space or are finished construction here on Earth, we can anticipate that thousands more exoplanets will be found. At the same time, we can anticipate that important details will be also discovered about these planets that were not possible before. Do they have atmospheres? Do they have oceans? Do they have mountain ranges and chasms? We hope to find out!

Further Reading: arXiv

What is the Radial Velocity Method?

Welcome back to our series on Exoplanet-Hunting methods! Today, we look at another widely-used and popular method of exoplanet detection, known as the Radial Velocity (aka. Doppler Spectroscopy) Method.

The hunt for extra-solar planets sure has heated up in the past decade or so! Thanks to improvements made in instrumentation and methodology, the number of exoplanets discovered (as of December 1st, 2017) has reached 3,710 planets in 2,780 star systems, with 621 system boasting multiple planets. Unfortunately, due to the limits astronomers are forced to contend with, the vast majority have been discovered using indirect methods.

When it comes to these indirect methods, one of the most popular and effective is the Radial Velocity Method – also known as Doppler Spectroscopy. This method relies on observing the spectra stars for signs of “wobble”, where the star is found to be moving towards and away from Earth. This movement is caused by the presence of planets, which exert a gravitational influence on their respective sun.

Continue reading “What is the Radial Velocity Method?”

Astronomers Find Another Solar System with 8 Planets. Uh, Pluto, About that Deplaneting…

In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle

With every passing year, more and more extra-solar planets are discovered. To make matters more interesting, improvements in methodology and technology are allowing for the discovery of more planets within individual systems. Consider the recent announcement of a seven-planet system around the red dwarf star known as TRAPPIST-1. At the time, this discovery established the record for most exoplanets orbiting a single star.

Well move over TRAPPIST-1! Thanks to the Kepler Space Telescope and machine learning, a team from Google AI and the Harvard-Smithsonian Center of Astrophysics (CfA) recently discovered an eighth planet in the distant star system of Kepler-90. Known as Kepler -90i, the discovery of this planet was made possible thanks to Google algorithms that detected evidence of a weak transit signal in the Kepler mission data.

Continue reading “Astronomers Find Another Solar System with 8 Planets. Uh, Pluto, About that Deplaneting…”

What is the Transit Method?

In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle

Welcome all to the first in our series on Exoplanet-hunting methods. Today we begin with the most popular and widely-used, known as the Transit Method (aka. Transit Photometry).

For centuries, astronomers have speculated about the existence of planets beyond our Solar System. After all, with between 100 and 400 billion stars in the Milky Way Galaxy alone, it seemed unlikely that ours was the only one to have a system of planets. But it has only been within the past few decades that astronomers have confirmed the existence of extra-solar planets (aka. exoplanets).

Astronomers use various methods to confirm the existence of exoplanets, most of which are indirect in nature. Of these, the most widely-used and effective to date has been Transit Photometry, a method that measures the light curve of distant stars for periodic dips in brightness. These are the result of exoplanets passing in front of the star (i.e. transiting) relative to the observer.

Description:

These changes in brightness are characterized by very small dips and for fixed periods of time, usually in the vicinity of 1/10,000th of the star’s overall brightness and only for a matter of hours. These changes are also periodic, causing the same dips in brightness each time and for the same amount of time. Based on the extent to which stars dim, astronomers are also able to obtain vital information about exoplanets.

For all of these reasons, Transit Photometry is considered a very robust and reliable method of exoplanet detection. Of the 3,526 extra-solar planets that have been confirmed to date, the transit method has accounted for 2,771 discoveries – which is more than all the other methods combined.

Advantages:

One of the greatest advantages of Transit Photometry is the way it can provide accurate constraints on the size of detected planets. Obviously, this is based on the extent to which a star’s light curve changes as a result of a transit.  Whereas a small planet will cause a subtle change in brightness, a larger planet will cause a more noticeable change.

When combined with the Radial Velocity method (which can determine the planet’s mass) one can determine the density of the planet. From this, astronomers are able to assess a planet’s physical structure and composition – i.e. determining if it is a gas giant or rocky planet. The planets that have been studied using both of these methods are by far the best-characterized of all known exoplanets.

In addition to revealing the diameter of planets, Transit Photometry can allow for a planet’s atmosphere to be investigated through spectroscopy. As light from the star passes through the planet’s atmosphere, the resulting spectra can be analyzed to determine what elements are present, thus providing clues as to the chemical composition of the atmosphere.

Artist’s impression of an extra-solar planet transiting its star. Credit: QUB Astrophysics Research Center

Last, but not least, the transit method can also reveal things about a planet’s temperature and radiation based on secondary eclipses (when the planet passes behind it’s sun). On this occasion, astronomers measure the star’s photometric intensity and then subtract it from measurements of the star’s intensity before the secondary eclipse. This allows for measurements of the planet’s temperature and can even determine the presence of clouds formations in the planet’s atmosphere.

Disadvantages:

Transit Photometry also suffers from a few major drawbacks. For one, planetary transits are observable only when the planet’s orbit happens to be perfectly aligned with the astronomers’ line of sight. The probability of a planet’s orbit coinciding with an observer’s vantage point is equivalent to the ratio of the diameter of the star to the diameter of the orbit.

Only about 10% of planets with short orbital periods experience such an alignment, and this decreases for planets with longer orbital periods. As a result, this method cannot guarantee that a particular star being observed does indeed host any planets. For this reason, the transit method is most effective when surveying thousands or hundreds of thousands of stars at a time.

It also suffers from a substantial rate of false positives; in some cases, as high as 40% in single-planet systems (based on a 2012 study of the Kepler mission). This necessitates that follow-up observations be conducted, often relying on another method. However, the rate of false positives drops off for stars where multiple candidates have been detected.

Number of extrasolar planet discoveries per year through September 2014, with colors indicating method of detection – radial velocity (blue), transit (green), timing (yellow), direct imaging (red), microlensing (orange). Credit: Public domain

While transits can reveal much about a planet’s diameter, they cannot place accurate constraints on a planet’s mass. For this, the Radial Velocity method (as noted earlier) is the most reliable, where astronomers look for signs of “wobble” in a star’s orbit to the measure the gravitational forces acting on them (which are caused by planets).

In short, the transit method has some limitations and is most effective when paired with other methods. Nevertheless, it remains the most widely-used means of “primary detection” – detecting candidates which are later confirmed using a different method – and is responsible for more exoplanet discoveries than all other methods combined.

Examples of Transit Photometry Surveys:

Transit Photometry is performed by multiple Earth-based and space-based observatories around the world. The majority, however, are Earth-based, and rely on existing telescopes combined with state-of-the-art photometers. Examples include the Super Wide Angle Search for Planets (SuperWASP) survey, an international exoplanet-hunting survey that relies on the Roque de los Muchachos Observatory and the South African Astronomical Observatory.

There’s also the Hungarian Automated Telescope Network (HATNet), which consists of six small, fully-automated  telescopes and is maintained by the Harvard-Smithsonian Center for Astrophysics. The MEarth Project is another, a National Science Foundation-funded robotic observatory that combines the Fred Lawrence Whipple Observatory (FLWO) in Arizona with the Cerro Tololo Inter-American Observatory (CTIO) in Chile.

The SuperWasp Cameras at the South African Astronomical Observatory. Credit: SuperWASP project & David Anderson

Then there’s the Kilodegree Extremely Little Telescope (KELT), an astronomical survey jointly administered by Ohio State University, Vanderbilt University, Lehigh University, and the South African Astronomical Society (SAAO). This survey consists of two telescopes, the Winer Observatory in southeastern Arizona and the Sutherland Astronomical Observation Station in South Africa.

In terms of space-based observatories, the most notable example is NASA’s Kepler Space Telescope. During its initial mission, which ran from 2009 to 2013, Kepler detected 4,496 planetary candidates and confirmed the existence of 2,337 exoplanets. In November of 2013, after the failure of two of its reaction wheels, the telescope began its K2 mission, during which time an additional 515 planets have been detected and 178 have been confirmed.

The Hubble Space Telescope also conducted transit surveys during its many years in orbit. For instance, the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) – which took place in 2006 – consisted of Hubble observing 180,000 stars in the central bulge of the Milky Way Galaxy. This survey revealed the existence of 16 additional exoplanets.

Other examples include the ESA’s COnvection ROtation et Transits planétaires (COROT) – in English “Convection rotation and planetary transits” – which operated from 2006 to 2012. Then there’s the ESA’s Gaia mission, which launched in 2013 with the purpose of creating the largest 3D catalog ever made, consisting of over 1 billion astronomical objects.

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

In March of 2018, the NASA Transiting Exoplanet Survey Satellite (TESS) is scheduled to be launched into orbit. Using the transit method, TESS will detect exoplanets and also select targets for further study by the James Webb Space Telescope (JSWT), which will be deployed in 2019. Between these two missions, the confirmation and characterization or many thousands of exoplanets is anticipated.

Thanks to improvements in terms of technology and methodology, exoplanet discovery has grown by leaps and bounds in recent years. With thousands of exoplanets confirmed, the focus has gradually shifted towards the characterizing of these planets to learn more about their atmospheres and conditions on their surface.

In the coming decades, thanks in part to the deployment of new missions, some very profound discoveries are expected to be made!

We have many interesting articles about exoplanet-hunting here at Universe Today. Here’s What are Extra Solar Planets?, What are Planetary Transits?, What is the Radial Velocity Method?, What is the Direct Imaging Method?, What is the Gravitational Microlensing Method?, and Kepler’s Universe: More Planets in our Galaxy than Stars.

Astronomy Cast also has some interesting episodes on the subject. Here’s Episode 364: The COROT Mission.

For more information, be sure to check out NASA’s page on Exoplanet Exploration, the Planetary Society’s page on Extrasolar Planets, and the NASA/Caltech Exoplanet Archive.

Sources:

Astronomers Find Comets Orbiting a Star 800 Light-Years Away

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

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

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

Exoplanet-Hunting Aliens Could Be Looking at Earth Right Now!

In the past few decades, the search for extra-solar planets has turned up a wealth of discoveries. Between the many direct and indirect methods used by exoplanet-hunters, thousands of gas giants, rocky planets and other bodies have been found orbiting distant stars. Aside from learning more about the Universe we inhabit, one of the main driving forces behind these efforts has been the desire to find evidence of Extra-Terrestrial Intelligence (ETI).

But suppose there are ETIs out there that are are also looking for signs of intelligence other than their own? How likely would they be to spot Earth? According to a new study by a team of astrophysicists from Queen’s University Belfast and the Max Planck Institute for Solar System Research in Germany, Earth would be detectable (using existing technology) from several star systems in our galaxy.

This study, titled “Transit Visibility Zones of the Solar System Planet“, was recently published in the Monthly Notices of the Royal Astronomical Society. Led by Robert Wells, a PhD student at the Astrophysics Research Center at Queen’s University Belfast, the team considered whether or not Earth would be detectable from other star systems using the Transit Method.

Diagram of a planet (e.g. the Earth, blue) transiting in front of its host star (e.g. the Sun, yellow). The lower black curve shows the brightness of the star noticeably dimming over the transit event, when the planet is blocking some of the light from the star. Credit: R. Wells.

This method consists of astronomers observing stars for periodic dips in brightness, which are attributed to planets passing (i.e. transiting) between them and the observer. For the sake of their study, Wells and his colleagues reversed the concept in order to determine if Earth would be visible to any species conducting observations from vantage points beyond our Solar System.

To answer this question, the team looked for parts of the sky from which one planet would be visible crossing the face of the Sun – aka. “transit zones”. Interestingly enough, they determined that the terrestrial planets that are closer to the Sun (Mercury, Venus, Earth and Mars) would easier to detect than the gas and ice giants – i.e.  Jupiter, Saturn, Uranus and Neptune.

While considerably larger, the gas/ice giants would be more difficult to detect using the transit method because of their long-period orbits. From Jupiter to Neptune, these planets take about 12 to 165 years to complete a single orbit! But more important than that is the fact that they orbit the Sun at much greater distances than the terrestrial planets. As Robert Wells indicated in a Royal Astronomical Society press statement:

”Larger planets would naturally block out more light as they pass in front of their star. However the more important factor is actually how close the planet is to its parent star – since the terrestrial planets are much closer to the Sun than the gas giants, they’ll be more likely to be seen in transit.”

How the transit zone of a Solar System planet is projected out from the Sun. The observer on the green exoplanet is situated in the transit zone and can therefore see transits of the Earth. Credit: R. Wells

Ultimately, what the team found was that at most, three planets could be observed from anywhere outside of the Solar System, and that not all combinations of these three planets was possible. For the most part, an observer would see only planet making a transit, and it would most likely be a rocky one. As Katja Poppenhaeger, a lecturer at the School of Mathematics and Physics at Queen’s University Belfast and a co-author of the study, explained:

“We estimate that a randomly positioned observer would have roughly a 1 in 40 chance of observing at least one planet. The probability of detecting at least two planets would be about ten times lower, and to detect three would be a further ten times smaller than this.”

What’s more, the team identified sixty-eight worlds where observers would be able to see one or more of the Solar planets making transits in front of the Sun. Nine of these planets are ideally situated to observe transits of the Earth, though none of them have been deemed to be habitable. These planets include HATS-11 b, 1RXS 1609 b, LKCA 15 b, WASP-68 b, WD 1145+017 b, and four planets in the WASP-47 system (b, c, d, e).

On top of that, they estimated (based on statistical analysis) that there could be as many as ten undiscovered and potentially habitable worlds in our galaxy which would be favorably located to detect Earth using our current level of technology. This last part is encouraging since, to date, not a single potentially habitable planet has been discovered where Earth could be seen making transits in front of the Sun.

Image showing where transits of our Solar System planets can be observed. Each line represents where one of the planets could be seen to transit, with the blue line representing Earth; an observer located here could detect us. Credit: 2MASS/A. Mellinger/R. Wells.

The team also indicated that further discoveries made by the Kepler and K2 missions will reveal additional exoplanets that have “a favorable geometric perspective to allow transit detections in the Solar System”. In the future, Wells and his team plan to study these transit zones to search for exoplanets, which will hopefully reveal some that could also be habitable.

One of the defining characteristics in the Search for Extra-Terrestrial Intelligence (SETI) has been the act of guessing about what we don’t know based on what we do. In this respect, scientists are forced to consider what extra-terrestrial civilizations would be capable of based on what humans are currently capable of. This is similar to how our search for potentially habitable planets is limited since we know of only one where life exists (i.e. Earth).

While it might seem a bit anthropocentric, it’s actually in keeping with our current frame of reference. Assuming that intelligent species could be looking at Earth using the same methods we do is like looking for planets that orbit within their star’s habitable zones, have atmospheres and liquid water on the surfaces.

In other words, it’s the “low-hanging fruit” approach. But thanks to ongoing studies and new discoveries, our reach is slowly extending further!

Further Reading: RAS, MNRAS

Advanced Civilizations Could Build a Galactic Internet with Planetary Transits

In a series of papers, Professor Loeb and Michael Hippke indicate that conventional rockets would have a hard time escaping from certain kinds of extra-solar planets. Credit: NASA/Tim Pyle

Decades after Enrico Fermi’s uttered his famous words – “Where is everybody?” – the Paradox that bears his name still haunts us. Despite repeated attempts to locate radio signals coming from space and our ongoing efforts to find visible indications of alien civilizations in distant star systems, the search extra-terrestrial intelligence (SETI) has yet to produce anything substantive.

Continue reading “Advanced Civilizations Could Build a Galactic Internet with Planetary Transits”

Finally! A Low Mass Super-Earth With Some Funky Atmosphere

In 2015, astronomers discovered an intriguing extrasolar planet located in a star system some 39 light years from Earth. Despite orbiting very close to its parent star, this “Venus-like” planet – known as GJ 1138b – appeared to still be cool enough to have an atmosphere. In short order, a debate ensued as to what kind of atmosphere it might have, whether it was a “dry Venus” or a “wet Venus”.

And now, thanks to the efforts of an international team of researchers, the existence of an atmosphere has been confirmed around GJ 1138b. In addition to settling the debate about the nature of this planet, it also marks the first time that an atmosphere has been detected around a low-mass Super-Earth. On top of that, GJ 1138b is now the farthest Earth-like planet that is known to have an atmosphere.

Led by John Southworth (of Keele University) and Luigi Mancini (of the University of Rome Tor Vergata), the research team included members from the Max Planck Institute for Astronomy (MPIA), the National Institute for Astrophysics (INAF), the University of Cambridge and Stockholm University. Their study, titled “Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b“, recently appeared in The Astrophysical Journal.

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

Using the GROND imager on the La Silla Observatory’s 2.2m ESO/MPG telescope, the team monitored GJ 1132b in different wavelengths as it transited in front of its parent star. Given the planet’s orbital period (1.6 days), these transits happen quite often, which presented plenty of opportunities to view it pass in front of its star. In so doing, they monitored the star for slight decreases in its brightness.

As Dr. Southworth explained to Universe via email, these observations confirmed the existence of an atmosphere:

“What we did was to measure the amount of dimming at 7 different wavelengths in optical and near-infrared light. At one of these wavelengths (IR) the planet seemed to be slightly bigger. This indicated that the planet has a large atmosphere around it which allows most of the starlight to pass through, but is opaque at one wavelength.”

The team members from the University of Cambridge and the MPIA then conducted simulations to see what this atmosphere’s composition could be. Ultimately, they concluded that it most likely has a thick atmosphere that is rich in water and/or methane – which contradicted recent theories that the planet had a thin and tenuous atmosphere (i.e. a “dry Venus”).

The ESO’s Paranal Observatory, located in the Atacama Desert of Chile. Credit: ESO

It was also the first time that an atmosphere has been confirmed around a planet that is not significantly greater in size and mass to Earth. In the past, astronomers have detected atmospheres around many other exoplanets. But in these cases, the planets were either gas giants or planets that were many times Earth’s size and mass (aka. “Super-Earths”). GJ 1132b, however, is 1.6 times as massive as Earth, and measures 1.4 Earth radii.

In addition, these findings are a significant step in the search for life beyond our Solar System. At present, astronomers seek to determine the chemical composition of a planet’s atmosphere to determine if it could be habitable. Where the right combination of chemical imbalances exist, the presence of living organisms is seen as a possible cause.

By being able to determine that a planet at lower end of the super-Earth scale has an atmosphere, we are one step closer to being able to determine exoplanet habitability. The detection of an atmosphere-bearing planet around an M-type (red dwarf) star is also good news in and of itself. Low-mass red dwarf stars are the most common star in the galaxy, and recent findings have indicated that they might be our best shot for finding habitable worlds.

Besides detecting several terrestrial planets around red dwarf stars in recent years – including seven around a single star (TRAPPIST-1) – there is also research that suggests that these stars are capable of hosting large numbers of planets. At the same time, there have been concerns about whether red dwarfs are too variable and unstable to support habitable worlds.

Artist’s impression of Kepler-1649b, the “Venus-like” world orbiting an M-class star 219 light-years from Earth. Credit: Danielle Futselaar

As Southworth explained, spotting an atmosphere around a planet that closely orbits a red dwarf could help bolster the case for red dwarf habitability:

“One of the big issues has been that very-low-mass stars typically have strong magnetic fields and thus throw out a lot of X-ray and ultraviolet light. These high-energy photons tend to destroy molecules in atmospheres, and might also evaporate them completely. The fact that we have detected an atmosphere around GJ 1132b means that this kind of planet is indeed capable of retaining an atmosphere for billions of years, even whilst being bombarded by the high-energy photons from their host stars.

In the future, GJ 1132b is expected to be a high-priority target for study with the Hubble Space Telescope, the Very Large Telescope (VLT) at the Paranal Observatory in Chile, and next-generation telescopes like the James Webb Space Telescope (scheduled for launch in 2018). Already, observations are being made, and the results are being eagerly anticipated.

I’m sure I’m not the only one who would like to hear what astronomers discover as they set their sights on this nearby star system and it’s Venus-like world! In the meantime, be sure to check out this video about GJ 1132b, courtesy of MIT news:

Further Reading: Max Planck Institute for Astronomy

Who Else Is Looking For Cool Worlds Around Proxima Centauri?

Finding exoplanets is hard work. In addition to requiring seriously sophisticated instruments, it also takes teams of committed scientists; people willing to pour over volumes of data to find the evidence of distant worlds. Professor Kipping, an astronomer based at the Harvard-Smithsonian Center for Astrophysics, is one such person.

Within the astronomical community, Kipping is best known for his work with exomoons. But his research also extends to the study and characterization of exoplanets, which he pursues with his colleagues at the Cool Worlds Laboratory at Columbia University. And what has interested him most in recent years is finding exoplanets around our Sun’s closest neighbor – Proxima Centauri.

Kipping describes himself as a “modeler”, combining novel theoretical modeling with modern statistical data analysis techniques applied to observations. He is also the Principal Investigator (PI) of The Hunt for Exomoons with Kepler (HEK) project and a fellow at the Harvard College Observatory. For the past few years, he and his team have been taking the hunt for exoplanets to the local stellar neighborhood.

The inspiration for this search goes back to 2012, when Kipping was at a conference and heard the news about a series of exoplanets being discovery around Kepler 42 (aka. KOI-961). Using data from the Kepler mission, a team from the California Institute of Technology discovered three exoplanets orbiting this red dwarf star, which is located about 126 light years from Earth.

At the time, Kipping recalled how the author of the study – Professor Philip Steven Muirhead, now an associate professor at the Institute for Astrophysical Research at Boston University – commented that this star system looked a lot like our nearest red dwarf stars – Barnard’s Star and Proxima Centauri.

In addition, Kepler 42’s planets were easy to spot, given that their proximity to the star meant that they completed an orbital period in about a day. Since they pass regularly in front of their star, the odds of catching sight of them using the Transit Method were good.

As Prof. Kipping told Universe Today via email, this was the “ah-ha moment” that would inspire him to look at Proxima Centauri to see if it too had a system of planets:

“We were inspired by the discovery of planets transiting KOI-961 by Phil Muirhead and his team using the Kepler data. The star is very similar to Proxima, a late M-dwarf harboring three sub-Earth sized planets very close to the star. It made me realize that if that system was around Proxima, the transit probability would be 10% and the star’s small size would lead to quite detectable signals.”

The MOST satellite, a Canadian built space telescope. Credit: Canadian Space Agency
The MOST satellite, a Canadian built space telescope. Credit: Canadian Space Agency

In essence, Kipping realized that if such a planetary system also existed around Proxima Centauri, a star with similar characteristics, then they would very easy to detect. After that, he and his team began attempting to book time with a space telescope. And by 2014-15, they had been given permission to use the Canadian Space Agency’s Microvariability and Oscillation of Stars (MOST) satellite.

Roughly the same size as a suitcase, the MOST satellite weighs only 54 kg and is equipped with an ultra-high definition telescope that measures just 15 cm in diameter. It is the first Canadian scientific satellite to be placed in orbit in 33 years, and was the first space telescope to be entirely designed and built in Canada.

Despite its size, MOST is ten times more sensitive than the Hubble Space Telescope. In addition, Kipping and his team knew that a mission to look for transiting exoplanets around Proxima Centauri would be too high-risk for something like Hubble. In fact, the CSA initially rejected their applications for this same reason.

“MOST initially denied us because they wanted to look at Alpha Centauri following the announcement by Dumusque et al. of a planet there,” said Kipping. “So understandably Proxima, for which no planets were known at the time, was not as high priority as Alpha Cen. We never even tried for Hubble time, it would be a huge ask to stare HST at a single star for months on end with just a a 10% chance for success.”

Artist's impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B iby the European Southern Observatory on October 17, 2012. Credit: ESO
Artist’s impression of the Earth-like exoplanet discovered orbiting Alpha Centauri B iby the European Southern Observatory on October 17, 2012. Credit: ESO

By 2014 and 2015, they secured permission to use MOST and observed Proxima Centauri twice – in May of both years. From this, they acquired a month and half’s-worth of space-based photometry, which they are currently processing to look for transits. As Kipping explained, this was rather challenging, since Proxima Centauri is a very active star – subject to star flares.

“The star flares very frequently and prominently in our data,” he said. “Correcting for this effect has been one the major obstacles in our analysis. On the plus side, the rotational activity is fairly subdued. The other issue we have is that MOST orbits the Earth once every 100 minutes, so we get data gaps every time MOST goes behind the Earth.”

Their efforts to find exoplanets around Proxima Centauri are especially significant in light of the European Southern Observatory’s recent announcement about the discovery of a terrestrial exoplanet within Proxima Centauri’s habitable zone (Proxima b). But compared to the ESO’s Pale Red Dot project, Kipping and his team were relying on different methods.

As Kipping explained, this came down to the difference between the Transit Method and the Radial Velocity Method:

“Essentially, we seek planets which have the right alignment to transit (or eclipse) across the face of the star, whereas radial velocities look for the wobbling motion of a star in response to the gravitational influence of an orbiting planet. Transits are always less likely to succeed for a given star, because we require the alignment to be just right. However, the payoff is that we can learn way more about the planet, including things like it’s size, density, atmosphere and presence of moons and rings.”

Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser
Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser

In the coming months and years, Kipping and his team may be called upon to follow up on the success of the ESO’s discovery. Having detected Proxima b using the Radial Velocity method, it now lies to astronomers to confirm the existence of this planet using another detection method.

In addition, much can be learned about a planet through the Transit Method, which would be helpful considering all the things we still don’t know about Proxima b. This includes information about its atmosphere, which the Transit Method is often able to reveal through spectroscopic measurements.

Suffice it to say, Kipping and his colleagues are quite excited by the announcement of Proxima b. As he put it:

“This is perhaps the most important exoplanet discovery in the last decade. It would be bitterly disappointing if Proxima b does not transit though, a planet which is paradoxically so close yet so far in terms of our ability to learn more about it. For us, transits would not just be the icing on the cake, serving merely as a confirmation signal – rather, transits open the door to learning the intimate secrets of Proxima, changing Proxima b from a single, anonymous data point to a rich world where each month we would hear about new discoveries of her nature and character.”

This coming September, Kipping will be joining the faculty at Columbia University, where he will continue in his hunt for exoplanets. One can only hope that those he and his colleagues find are also within reach!

Further Reading: Cool Worlds