Posted on by Matt Williams

Kepler’s Almost Out of Fuel. It’ll Make its Last Observation in a Few Months

Artist's concept of the Kepler mission with Earth in the background. Credit: NASA/JPL-Caltech
Artist's concept of the Kepler mission with Earth in the background. Credit: NASA/JPL-Caltech

Since its deployment in March of 2009, the Kepler space telescope has been a boon for exoplanet-hunters. As of March 8th, 2018, a total of 3,743 exoplanets have been confirmed, 2,649 of which were discovered by Kepler alone. At the same time, the telescope has suffered its share of technical challenges. These include the failure of two reaction wheels, which severely hampered the telescope’s ability to conduct its original mission.

Nevertheless, the Kepler team was able to return the telescope to a stable configuration by using small amounts of thruster fuel to compensate for the failed reaction wheels. Unfortunately, after almost four years conducting its K2 observation campaign, the Kepler telescope is now running out fuel. Based on its remaining fuel and rate of consumption, NASA estimates that the telescope’s mission will end in a few months.

For years, the Kepler space telescope has been locating planets around distant stars using the Transit Method (aka. Transit Photometry). This consists of monitors stars for periodic dips in brightness, which are caused by a planet passing in front of the star (i.e. transiting). Of all the methods used to hunt for exoplanets, the Transit Method is considered the most reliable, accounting for a total of 2900 discoveries.

Naturally, this news comes as a disappointment to astronomers and exoplanet enthusiasts. But before anyone starts lamenting the situation, they should keep some things in mind. For one, the Kepler mission has managed to last longer than anyone expected. Ever since the K2 campaign began, the telescope has been required to shift its field of view about every three months to conduct a new observation campaign.

Based on their original estimates, the Kepler team believed they had enough fuel to conduct 10 more campaigns. However, the mission has already completed 16 campaigns and the team just began their 17th. As Charlie Sobeck, a system engineer for the Kepler space telescope mission, explained in a recent NASA press statement:

“Our current estimates are that Kepler’s tank will run dry within several months – but we’ve been surprised by its performance before! So, while we anticipate flight operations ending soon, we are prepared to continue as long as the fuel allows. The Kepler team is planning to collect as much science data as possible in its remaining time and beam it back to Earth before the loss of the fuel-powered thrusters means that we can’t aim the spacecraft for data transfer. We even have plans to take some final calibration data with the last bit of fuel, if the opportunity presents itself.”

So while the mission is due to end soon, the science team hopes to gather as much scientific data as possible and beam it back to Earth before then. They also hope to gather some final calibration data using the telescope’s last bit of fuel, should the opportunity present itself. And since they cannot refuel the spacecraft, they hope to stop collecting data so they can use their last bit of fuel to point the spacecraft back towards Earth and bring it home.

NASA’s Kepler spacecraft has been on an extended mission called K2 after two of its four reaction wheels failed in 2013. Credit: NASA

“Without a gas gauge, we have been monitoring the spacecraft for warning signs of low fuel— such as a drop in the fuel tank’s pressure and changes in the performance of the thrusters,” said Sobeck. “But in the end, we only have an estimate – not precise knowledge. Taking these measurements helps us decide how long we can comfortably keep collecting scientific data.”

This has been standard practice for many NASA missions, where enough fuel has been reserved to conduct one last maneuver. For example, the Cassini mission had to reserve fuel in order to descend into Saturn’s atmosphere so it would avoid colliding with one of its moons and contaminating a potentially life-bearing environment. Satellites also regularly conduct final maneuvers to ensure they don’t crash into other satellites or fall to Earth.

While deep-space missions like Kepler are in no danger of crashing to Earth or contaminating a sensitive environment, this final maneuver is designed to ensure that the science team can squeeze every last drop of data from the spacecraft. So before the mission wraps up, we can expect that this venerated planet-hunter will have some final surprises for us!

Artist’s rendition of TESS in space. (Credit: MIT Kavli Institute for Astrophysics Research).

In the coming years, next-generation telescopes will be taking to space to pick up where Kepler and other space telescopes left off. These include the Transiting Exoplanet Survey Satellite (TESS), which will be conducting Transit surveys shortly after it launches in April of 2018. By 2019, the James Webb Space Telescope (JWST) will also take to space and use its powerful infrared instruments to aid in the hunt for exoplanets.

So while we will soon be saying goodbye to the Kepler mission, its legacy will live on. In truth, the days of exoplanet discovery are just getting started!

Stay tuned for updates from the Kepler and K2 Science Center.

Further Reading: NASA

Posted on by Matt Williams

Proxima Centauri Just Released a Deadly Flare, so it’s Probably not a Great Place for Habitable Planets

Artist impression of a red dwarf star like Proxima Centauri, the nearest star to our sun. New analysis of ALMA observations reveal that Proxima Centauri emitted a powerful flare that would have created inhospitable conditions for planets in that system. Credit: NRAO/AUI/NSF; D. Berry

Since it’s discovery was announced in August of 2016, Proxima b has been an endless source of wonder and the target of many scientific studies. As the closest extra-solar planet to our Solar System – and a terrestrial planet that orbits within Proxima Centauri’s circumstellar habitable zone (aka. “Goldilocks Zone”) – scientists have naturally wondered whether or not this planet could be habitable.

Unfortunately, many of these studies have emphasized the challenges that life on Proxima b would likely face, not the least of which is harmful radiation from its star. According to a recent study, a team of astronomers used the ALMA Observatory to detect a large flare emanating from Proxima Centauri. This latest findings, more than anything, raises questions about how habitable its exoplanet could be.

The study, titled “Detection of a Millimeter Flare from Proxima Centauri“, recently appeared in The Astrophysical Journal Letters. Led by Meredith A. MacGregor, an NSF Astronomy and Astrophysics Postdoctoral Fellow at the Carnegie Institution for Science, the team also included members from the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Colorado Boulder.

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser

For the sake of their study, the team used data obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) between January 21st to April 25th, 2017. This data revealed that the star underwent a significant flaring event on March 24th, where it reached a peak that was 1000 times brighter than the star’s quiescent emission for a period of ten seconds.

Astronomers have known for a long time that when compared to stars like our Sun, M-type stars are variable and unstable. While they are the smallest, coolest, and dimmest stars in our Universe, they tend to flare up at a far greater rate. In this case, the flare detected by the team was ten times larger than our Sun’s brightest flares at similar wavelengths.

Along with a smaller preceding flare, the entire event lasted fewer than two minutes of the 10 hours that ALMA was observing the star between January and March of last year. While it was already known that Proxima Centauri, like all M-type stars, experiences regular flare activity, this one appeared to be a rare event. However, stars like Proxima Centauri are also known to experienced regular, although smaller, X-ray flares.

All of this adds up to a bad case for habitability. As MacGregor explained in a recent NRAO press statement:

“It’s likely that Proxima b was blasted by high energy radiation during this flare. Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”

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

MacGregor and her colleagues also considered the possibility that Proxima Centauri is circled by several disks of dust. This was suggested by a previous study (also based on ALMA data) that indicated that the light output of both the star and flare together pointed towards the existence of debris belts around the star. However, after examining the ALMA data as a function of observing time, they were able to eliminate this as a possibility.

As Alycia J. Weinberger, also a researcher with the Carnegie Institution for Science and a co-author on the paper, explained:

“There is now no reason to think that there is a substantial amount of dust around Proxima Cen. Nor is there any information yet that indicates the star has a rich planetary system like ours.”

To date, studies that have looked at possible conditions on Proxima b have come to different conclusions as to whether or not it could retain an atmosphere or liquid water on its surface. While some have found room for “transient habitability” or evidence of liquid water, others have expressed doubt based on the long-term effects that radiation and flares from its star would have on a tidally-locked planet.

In the future, the deployment of next-generation instruments like the James Webb Space Telescope are expected to provide more detailed information on this system. With precise measurements of this star and its planet, the question of whether or not life can (and does) exist in this system may finally be answered.

And be sure to enjoy this animation of Proxima Centauri in motion, courtesy of NRAO outreach:

Further Reading: NRAO, The Astrophysical Journal Letters

Posted on by Matt Williams

Researchers Just Scanned 14 Worlds From the Kepler Mission for “Technosignatures”, Evidence of Advanced Civilizations

A team of astronomers from UCLA searched for "technosignatures" in the Kepler field data. Credit and Copyright: Danielle Futselaar

When it comes to looking for life on extra-solar planets, scientists rely on what is known as the “low-hanging fruit” approach. In lieu of being able to observe these planets directly or up close, they are forced to look for “biosignatures” – substances that indicate that life could exist there. Given that Earth is the only planet (that we know of) that can support life, these include carbon, oxygen, nitrogen and water.

However, while the presence of these elements are a good way of gauging “habitability”, they are not necessarily indications that extra-terrestrial civilizations exist. Hence why scientists engaged in the Search for Extra-Terrestrial Intelligence (SETI) also keep their eyes peeled for “technosignatures”. Targeting the Kepler field, a team of scientists recently conducted a study that examined 14 planetary systems for indications of intelligent life.

The study, titled “A search for technosignatures from 14 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz“, recently appeared online and is being reviewed for publication by The Astronomical Journal. The team was led by Jean-Luc Margot, the Chair of the UCLA Department of Earth, Planetary, and Space Sciences (UCLA EPSS) and a Professor with UCLA’s Department of Physics and Astronomy.

The Green Bank Telescope is the world’s largest, fully-steerable telescope, which is currently being used in a new SETI (Search for Extraterrestrial Intelligence) attempt to look for possible alien radio signals from Tabby’s Star. Credit: NRAO/AUI/NSF

In addition to Margot, the team consisted of 15 graduate and undergraduate students from UCLA and a postdoctoral researcher from the Green Bank Observatory and the Center for Gravitational Waves and Cosmology at West Virginia University. All of the UCLA students participated in the 2016 course, “Search for Extraterrestrial Intelligence: Theory and Applications“.

Together, the team selected 14 systems from the Kepler catalog and examined them for technosignatures. While radio waves are a common occurrence in the cosmos, not all sources can be easily attributed to natural causes. Where and when this is the case, scientists conduct additional studies to try and rule out the possibility that they are a technosignature. As Professor Margot told Universe Today via email:

“In our article, we define a “technosignature” as any measurable property or effect that provides scientific evidence of past or present technology, by analogy with “biosignatures,” which provide evidence of past or present life.”

For the sake of their study, the team conducted an L-band radio survey of these 14 planetary systems. Specifically, they looked for signs of radio waves in the 1.15 to 1.73 gigahertz (GHz) range. At those frequencies, their study is sensitive to Arecibo-class transmitters located within 450 light-years of Earth. So if any of these systems have civilizations capable of building radio observatories comparable to Arecibo, the team hoped to find out!

Spring 2016 UCLA SETI class with Larry Lesyna. Credit: UCLA

“We searched for signals that are narrow (< 10 Hz) in the frequency domain,” said Margot. “Such signals are technosignatures because natural sources do not emit such narrowband signals… We identified approximately 850,000 candidate signals, of which 19 were of particular interest. Ultimately, none of these signals were attributable to an extraterrestrial source.”

What they found was that of the 850,000 candidate signals, about 99% of them were automatically ruled out because they were quickly determined to be the result of human-generated radio-frequency interference (RFI). Of the remaining candidates, another 99% were also flagged as anthropogenic because their frequencies overlapped with other known sources of RFI – such as GPS systems, satellites, etc.

The 19 candidate signals that remained were heavily scrutinized, but none could be attributed to an extraterrestrial source. This is key when attempting to distinguish potential signs of intelligence from radio signals that come from the only intelligence we know of (i.e. us!) Hence why astronomers have historically been intrigued by strong narrowband signals (like the WOW! Signal, detected in 1977) and the Lorimer Burst detected in 2007.

In these cases, the sources appeared to be coming from the Messier 55 globular cluster and the Large Magellanic Cloud, respectively. The latter was especially fascinating since it was the first time that astronomers had observered what are now known as Fast Radio Bursts (FRBs). Such bursts, especially when they are repeating in nature, are considered to be one of the best candidates in the search for intelligent, technologically-advanced life.

The UCLA SETI Group banner, featuring a photo of the central region of the Milky Way Galaxy. Credit: Yuri Beletsky/Carnegie Las Campanas Observatory

Unfortunately, these sources are still being investigated and scientists cannot attribute them to unnatural causes just yet. And as Professor Margot indicated, this study (which covered only 14 of the many thousand exoplanets discovered by Kepler) is just the tip of the iceberg:

“Our study encompassed only a small fraction of the search volume.  For instance, we covered less than five-millionths of the entire sky.  We are eager to scale the effort to sample a larger fraction of the search volume. We are currently seeking funds to expand our search.”

Between Kepler‘s first and second mission (K2), a total of 5,118 candidates and 2,538 confirmed exoplanets have been discovered within our galaxy alone. As of February 1st, 2018, a grand total of 3,728 exoplanets have been confirmed in 2,794 systems, with 622 systems having more than one planet. On top of that, a team of researchers from the University of Oklahoma recently made the first detection of extra-galactic planets as well!

It would therefore be no exaggeration to say that the hunt for ETI is still in its infancy, and our efforts are definitely beginning to pick up speed. There is literally a Universe of possibilities out there and to think that there are no other civilizations that are also looking for us seems downright unfathomable. To quote the late and great Carl Sagan: “The Universe is a pretty big place. If it’s just us, seems like an awful waste of space.”

And be sure to check out this video of the 2017 UCLA SETI Group, courtesy of the UCLA EPSS department:

Further Reading: arXiv

Posted on by Matt Williams

For the First Time, Planets Have Been Discovered in ANOTHER Galaxy!

Using the microlensing metthod, a team of astrophysicists have found the first extra-galactic planets! Credit: NASA/Tim Pyle

The first confirmed discovery of a planet beyond our Solar System (aka. an Extrasolar Planet) was a groundbreaking event. And while the initial discoveries were made using only ground-based observatories, and were therefore few and far between, the study of exoplanets has grown considerably with the deployment of space-based telescopes like the Kepler space telescope.

As of February 1st, 2018, 3,728 planets have been confirmed in 2,794 systems, with 622 systems having more than one planet. But now, thanks to a new study by a team of astrophysicists from the University of Oklahoma, the first planets beyond our galaxy have been discovered! Using a technique predicting by Einstein’s Theory of General Relativity, this team found evidence of planets in a galaxy roughly 3.8 billion light years away.

The study which details their discovery, titled “Probing Planets in Extragalactic Galaxies Using Quasar Microlensing“, recently appeared in The Astrophysical Journal Letters. The study was conducted by Xinyu Dai and Eduardo Guerras, a postdoctoral researcher and professor from the Homer L. Dodge Department of Physics and Astronomy at the University of Oklahoma, respectively.

For the sake of their study, the pair used the Gravitational Microlensing technique, which relies on the gravitational force of distant objects to bend and focus light coming from a star. As a planet passes in front of the star relative to the observer (i.e. makes a transit), the light dips measurably, which can then be used to determine the presence of a planet.

In this respect, Gravitational Microlensing is a scaled-down version of Gravitational Lensing, where an intervening object (like a galaxy cluster) is used to focus light coming from a galaxy or other large object located beyond it. It also incorporates a key element of the highly-effective Transit Method, where stars are monitored for dips in brightness to indicate the presence of an exoplanet.

In addition to this method, which is the only one capable of detecting extra-solar planets at truly great distances (on the order of billions of light years), the team also used data from NASA’s Chandra X-ray Observatory to study a distant quasar known as RX J1131–1231. Specifically, the team relied on the microlensing properties of the supermassive black hole (SMBH) located at the center of RX J1131–1231.

They also relied on the OU Supercomputing Center for Education and Research to calculate the microlensing models they employed. From this, they observed line energy shifts that could only be explained by the presence of of about 2000 unbound planets between the quasar’s stars – which ranged from being as massive as the Moon to Jupiter – per main-sequence star.

Image of the gravitational lens RX J1131-1231 galaxy with the lens galaxy at the center and four lensed background quasars. It is estimated that there are trillions of planets in the center elliptical galaxy in this image. Credit: University of Oklahoma

As Xinyu Dai explained in a recent University of Oklahoma press release:

“We are very excited about this discovery. This is the first time anyone has discovered planets outside our galaxy. These small planets are the best candidate for the signature we observed in this study using the microlensing technique. We analyzed the high frequency of the signature by modeling the data to determine the mass.”

While 53 planets have been discovered within the Milky Way galaxy using the Microlensing technique, this is the first time that planets have been observed in other galaxies. Much like the first confirmed discovery of an extra-solar planet, scientists were not even certain planets existed in other galaxies prior to this study. This discovery has therefore brought the study of planets beyond our Solar System to a whole new level!

And as Eduardo Guerras indicated, the discovery was possible thanks to improvements made in both modelling and instrumentation in recent years:

“This is an example of how powerful the techniques of analysis of extragalactic microlensing can be. This galaxy is located 3.8 billion light years away, and there is not the slightest chance of observing these planets directly, not even with the best telescope one can imagine in a science fiction scenario. However, we are able to study them, unveil their presence and even have an idea of their masses. This is very cool science.”

In the future, exoplanet discoveries are likely to be made within and beyond the Milky Way Galaxy. Credit: NASA

In the coming years, more sophisticated observatories will be available, which will allow for even more in the way of discoveries. These include space-based instruments like the James Webb Space Telescope (which is scheduled to launch in Spring of 2019) and ground-based observatories like the ESO’s OverWhelmingly Large (OWL) Telescope, the Very Large Telescope (VLT), the Extremely Large Telescope (ELT), and the Colossus Telescope.

At this juncture, the odds are good that some of these discoveries will be in neighboring galaxies. Perhaps then we can begin to determine just how common planets are in our Universe. At present, it is estimated that could be as many as 100 billion planets in the Milky Way Galaxy alone! But with an estimated 1 to 2 trillion galaxies in the Universe… well, you do the math!

Further Reading: University of Oklahoma, The Astrophysical Journal Letters

Posted on by Matt Williams

The New Earth-Sized Planet Hunting Telescope ExTrA is Now Online

The ExTrA telescopes are sited at ESO’s La Silla Observatory in Chile. They will be used to search for and study Earth-sized planets orbiting nearby red dwarf stars. Credit: ESO/Emmanuela Rimbaud

Ever since the Kepler space telescope began discovering thousands of exoplanets in our galaxy, astronomers have been eagerly awaiting the day when next-generation missions are deployed. These include the much-anticipated James Webb Space Telescope, which is scheduled to take to space in 2019, but also the many ground-based observatories that are currently being constructed.

One of these is the Exoplanets in Transits and their Atmospheres (ExTrA) project, which is the latest addition to the ESO’s La Silla Observatory in Chile. Using the Transit Method, this facility will rely on three 60-centimeter (23.6 in) telescopes to search for Earth-sized exoplanets around M-type (red dwarf) stars in the Milky Way Galaxy. This week, the facility began by collecting its first light.

The Transit Method (aka. Transit Photometry) consists of monitoring stars for periodic dips in brightness. These dips are caused by planets passing in front of the star (aka. transiting) relative to the observer. In the past, detecting planets around M-type stars using this method has been challenging since red dwarfs are the smallest and dimmest class of star in the known Universe and emit the majority of their light in the near-infrared band.

Artist’s impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

However, these stars have also proven to be treasure trove when it comes to rocky, Earth-like exoplanets. In recent years, rocky planets have been discovered around star’s like Proxima Centauri and Ross 128, while TRAPPIST-1 had a system of seven rocky planets. In addition, there have been studies that have indicated that potentially-habitable, rocky planets could be very common around red dwarf stars.

Unlike other facilities, the ExTrA project is well-suited to conduct surveys for planets around red dwrfs because of its location on the outskirts of the Atacama Desert in Chile. As Xavier Bonfils, the project’s lead researcher, explained:

“La Silla was selected as the home of the telescopes because of the site’s excellent atmospheric conditions. The kind of light we are observing – near-infrared – is very easily absorbed by Earth’s atmosphere, so we required the driest and darkest conditions possible. La Silla is a perfect match to our specifications.”

In addition, the ExTrA facility will rely on a novel approach that involves combining optical photometry with spectroscopic information. This consists of its three telescopes collecting light from a target star and four companion stars for comparison. This light is then fed through optical fibers into a multi-object spectrograph in order to analyze it in many different wavelengths.

The ExTrA telescopes are sited at ESO’s La Silla Observatory in Chile. Credit: ESO/Petr Horálek

This approach increases the level of achievable precision and helps mitigate the disruptive effect of Earth’s atmosphere, as well as the potential for error introduced by instruments and detectors. Beyond the goal of simply finding planets transiting in front of their red dwarf stars, the ExTrA telescopes will also study the planets it finds in order to determine their compositions and their atmospheres.

In short, it will help determine whether or not these planets could truly be habitable. As Jose-Manuel Almenara, a member of the ExTrA team, explained:

“With ExTrA, we can also address some fundamental questions about planets in our galaxy. We hope to explore how common these planets are, the behaviour of multi-planet systems, and the sorts of environments that lead to their formation,”

The potential to search for extra-solar planets around red dwarf stars is an immense opportunity for astronomers. Not only are they the most common star in the Universe, accounting for 70% of stars in our galaxy alone, they are also very long-lived. Whereas stars like our Sun have a lifespan of about 10 billion years, red dwarfs are capable of remaining in their main sequence phase for up to 10 trillion years.

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser

For these reasons, there are those who think that M-type stars are our best bet for finding habitable planets in the long run. At the same time, there are unresolved questions about whether or not planets that orbit red dwarf stars can stay habitable for long, owing to their variability and tendency to flare up. But with ExTrA and other next-generation instruments entering into service, astronomers may be able to address these burning questions.

As Bonfils excitedly put it:

“With the next generation of telescopes, such as ESO’s Extremely Large Telescope, we may be able to study the atmospheres of exoplanets found by ExTra to try to assess the viability of these worlds to support life as we know it. The study of exoplanets is bringing what was once science fiction into the world of science fact.”

ExTrA is a French project funded by the European Research Council and the French Agence National de la Recherche and its telescopes will be operated remotely from Grenoble, France. Also, be sure to enjoy this video of the ExTrA going online, courtesy of the ESOcast:

Further Reading: ESO

Posted on by Matt Williams

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

Using the microlensing metthod, a team of astrophysicists have found the first extra-galactic planets! Credit: NASA/Tim Pyle

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

Posted on by Matt Williams

What is the Gravitational Microlensing Method?

Hubble image of a luminous red galaxy (LRG) gravitationally distorting the light from a much more distant blue galaxy, a technique known as gravitational lensing. The shape of the galaxy doing the lensing created an almost circular image. An oblong galaxy would create more of an Einstein Ring effect. Credit: ESA/Hubble & NASA
Hubble image of a luminous red galaxy (LRG) gravitationally distorting the light from a much more distant blue galaxy, a technique known as gravitational lensing. The shape of the galaxy doing the lensing created an almost circular image. An oblong galaxy would create more of an Einstein Ring effect. Credit: ESA/Hubble & NASA

Welcome back to our series on Exoplanet-Hunting methods! Today, we look at the curious and unique method known as Gravitational Microlensing.

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

One of the more commonly-used methods for indirectly detecting exoplanets is known as Gravitational Microlensing. Essentially, this method relies on the gravitational force of distant objects to bend and focus light coming from a star. As a planet passes in front of the star relative to the observer (i.e. makes a transit), the light dips measurably, which can then be used to determine the presence of a planet.

In this respect, Gravitational Microlensing is a scaled-down version of Gravitational Lensing, where an intervening object (like a galaxy cluster) is used to focus light coming from a galaxy or other object located beyond it. It also incorporates a key element of the highly-effective Transit Method, where stars are monitored for dips in brightness to indicate the presence of an exoplanet.

Description:

In accordance with Einstein’s Theory of General Relativity, gravity causes the fabric of spacetime to bend. This effect can cause light affected by an object’s gravity to become distorted or bent. It can also act as a lens, causing light to become more focused and making distant objects (like stars) appear brighter to an observer. This effect occurs only when the two stars are almost exactly aligned relative to the observer (i.e. one positioned in front of the other).

These “lensing events” are brief, but plentiful, as Earth and stars in our galaxy are always moving relative to each other. In the past decade, over one thousand such events have been observed, and typically lasted for a few days or weeks at a time. In fact, this effect was used by Sir Arthur Eddington in 1919 to provide the first empirical evidence for General Relativity.

This took place during the solar eclipse of May 29th, 1919, where Eddington and a scientific expedition traveled to the island of Principe off the coast of West Africa to take pictures of the stars that were now visible in the region around the Sun. The pictures confirmed Einstein’s prediction by showing how light from these stars was shifted slightly in response to the Sun’s gravitational field.

The technique was originally proposed by astronomers Shude Mao and Bohdan Paczynski in 1991 as a means of looking for binary companions to stars. Their proposal was refined by Andy Gould and Abraham Loeb in 1992 as a method of detecting exoplanets. This method is most effective when looking for planets towards the center of the galaxy, as the galactic bulge provides a large number of background stars.

A sketch of a microlensing signature with a planet in the lens system. Image Credit: NASA / ESA / K. Sahu / STScI

Advantages:

Microlensing is the only known method capable of discovering planets at truly great distances from the Earth and is capable of finding the smallest of exoplanets. Whereas the Radial Velocity Method is effective when looking for planets up to 100 light years from Earth and Transit Photometry can detect planets hundreds of light-years away, microlensing can find planets that are thousands of light-years away.

While most other methods have a detection bias towards smaller planets, the microlensing method is the most sensitive means of detecting planets that are around 1-10 astronomical units (AU) away from Sun-like stars. Microlensing is also the only proven means of detecting low-mass planets in wider orbits, where both the transit method and radial velocity are ineffective.

Taken together, these benefits make microlensing the most effective method for finding Earth-like planets around Sun-like stars. In addition, microlensing surveys can be effectively mounted using ground-based facilities. Like Transit Photometry, the Microlensing Method benefits from the fact that it can be used to survey tens of thousands of stars simultaneously.

Disadvantages:

Because microlensing events are unique and not subject to repeat, any planets detected using this method will not be observable again. In addition, those planets that are detected tend to be very far way, which makes follow-up investigations virtually impossible. Luckily, microlensing detections generally do not require follow-up surveys since they have a very high signal-to-noise ratio.

While confirmation is not necessary, some planetary microlensing events have been confirmed. The planetary signal for event OGLE-2005-BLG-169 was confirmed by HST and Keck observations (Bennett et al. 2015; Batista et al. 2015). In addition, microlensing surveys can only produce rough estimations of a planet’s distance, leaving significant margins for error.

Microlensing is also unable to yield accurate estimates of a planet’s orbital properties, since the only orbital characteristic that can be directly determined with this method is the planet’s current semi-major axis. As such, planet’s with an eccentric orbit will only be detectable for a tiny portion of its orbit (when it is far away from its star).

Finally, microlensing is dependent on rare and random events – the passage of one star precisely in front of another, as seen from Earth – which makes detections both rare and unpredictable.

Examples of Gravitational Microlensing Surveys:

Surveys that rely on the Microlensing Method include the Optical Gravitational Lensing Experiment (OGLE) at the University of Warsaw. Led by Andrzej Udalski, the director of the University’s Astronomical Observatory, this international project uses the 1.3 meter “Warsaw” telescope at Las Campanas, Chile, to search for microlensing events in a field of 100 stars around the galactic bulge.

The Astronomical Observatory at the University of Warsaw, used to conduct the OGLE project. Credit: ogle.astrouw.edu.pl

There is also the Microlensing Observations in Astrophysics (MOA) group, a collaborative effort between researchers in New Zealand and Japan. Led by Professor Yasushi Muraki of Nagoya University, this group uses the Microlensing Method to conduct surveys for dark matter, extra-solar planets, and stellar atmospheres from the southern hemisphere.

And then there’s the Probing Lensing Anomalies NETwork (PLANET), which consists of five 1-meter telescopes distributed around the southern hemisphere. In collaboration with RoboNet, this project is able to provide near-continuous observations for microlensing events caused by planets with masses as low as Earth’s.

The most sensitive survey to date is the Korean Microlensing Telescope Network (KMTNet), a project initiated by the Korea Astronomy and Space Science Institute (KASI) in 2009. KMTNet relies on the instruments at three southern observatories to provide 24-hour continuous monitoring of the Galactic bulge, searching for microlensing events that will point the way towards earth-mass planets orbiting with their stars habitable zones.

We have written many interesting articles on exoplanet detection here at Universe Today. Here is What are Extra Solar Planets?, What is the Transit Method?, What is the Radial Velocity Method?, What is Gravitational Lensing? and Kepler’s Universe: More Planets in our Galaxy than Stars

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.

Astronomy Cast also has relevant episodes on the subject. Here’s Episode 208: The Spitzer Space Telescope, Episode 337: Photometry, Episode 364: The CoRoT Mission, and Episode 367: Spitzer Does Exoplanets.

Sources:

Posted on by Matt Williams

What is the Radial Velocity Method?

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser

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?”

Posted on by Matt Williams

Astronomers Figure Out a New Way to Search for Planets at Alpha Centauri

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

At a distance of 4.37 light-years from Earth, Alpha Centauri is the nearest star system to our own. For generations, scientists and speculative thinkers have pondered whether it might have a planetary system like our own Sun, and whether or not life may also exist there. Unfortunately, recent efforts to locate extra-solar planets in this star system have failed, with potential detections later shown to be the result of artifacts in the data.

In response to these failed efforts, several more ambitious projects are being developed to find exoplanets around Alpha Centauri. These include direct-imaging space telescopes like Project Blue and the interstellar mission known as Breakthrough Starshot. But according to a new study led by researchers from Yale University, existing data can be used to determine the probability of planets in this system (and even which kind).

The study which detailed their findings recently appeared in The Astronomical Journal under the title “Planet Detectability in the Alpha Centauri System“. The study was led by Lily Zhao, a graduate student from Yale University and a fellow with the National Science Foundation (NSF), and was co-authored by Debora Fischer, John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of the Universidad Andrés Bello in Chile.

Artist’s impression of what the surface might look like on a planet orbiting Alpha Centauri system. Credit: Michael S. Helfenbein

For the sake of their study, Zhao and her team considered why efforts to locate planets within the the closest star system to our own have so far failed. This is surprising when one considers how, statistically speaking, Alpha Centauri is very likely to have a system if its own. As Prof. Fischer indicated in a recent Yale News press release:

“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B… Because Alpha Centauri is so close, it is our first stop outside our solar system. There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”

In addition to being a professor of astronomy at Yale University, Debora Fischer is also one of the leaders of the Yale Exoplanets Group. As an expert in her field, Fischer has devoted decades of her life to researching exoplanets and searching for Earth analogues beyond our Solar System. With partial funding provided by NASA and the National Science Foundation, the team relied on existing data collected by some of the latest exoplanet-hunting instruments.

These included CHIRON, a spectrograph mounted on the Small and Moderate Aperture Research Telescope System (SMARTS) at the Cerro Telolo Inter-American Observatory (CTIO) in Chile. This instrument was built by Fischer’s team, and the data it provided was combined with the High Accuracy Radial velocity Planet Searcher (HARPS) and the Ultraviolet and Visual Echelle Spectrograph (UVES) instruments on the ESO’s Very Large Telescope (VLT).

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

Using ten years of data collected by these instruments, Zhao and her colleagues then set up a grid system for the Alpha Centauri system. Rather than looking for signs of planets that did exist, they used the data to rule out what types of planets could not exist there. As Zhao told Universe Today via email:

“This study was special in that it used existing data of the Alpha Centauri system not to find planets, but to characterize what planets could not exist. By doing so, it returned more information about the system as a whole and provides guidance for future observations of this uniquely charismatic system. 

In addition, the team analyzed the chemical composition of the stars in the Alpha Centauri system to learn more about the kinds of material that would be available to form planets. Based on the different values obtained by observations campaigns conducted by different telescopes on Alpha Centauri’s three stars (Alpha, Beta and Proxima), they were able to place constraints on what kinds of planets could exist there. 

“We found that existing data rules out planets in the habitable zone above 53 Earth masses for alpha Centauri A, 8.4 Earth masses for Alpha Centauri B, and 0.47 Earth masses for Proxima Centauri,” said Zhao. “As for the chemical compositions, we found that the ratios of Carbon/Oxygen and Magnesium/Silicon for Alpha Centauri A and B are quite similar to that of the Sun.”

Artist’s impression of how the surface of a planet orbiting a red dwarf star may appear. Credit: M. Weiss/CfA

Basically, the results of their study effectively ruled out the possibility of any Jupiter-sized gas giants in the Alpha Centauri system. For Alpha Centauri A, they further found that planets that were less than 50 Earth masses could exist, while Alpha Centauri B might have planets smaller than 8 Earth masses. For Proxima Centauri, which we know to have at least one Earth-like planet, they determined that there might more that are less than half of Earth’s mass.

In addition to offering hope for exoplanet-hunters, this study carries with it some rather interesting implications for planetary habitability. Basically, the presence of rocky planets in the system is encouraging; but with no gas giants, a key ingredient in ensuring that planets remain habitable could be missing.

“[N]ot only could there still be habitable, Earth-mass planets around our closest stellar neighbors, but there also aren’t any gas giants that could endanger the survival of these potentially habitable, rocky planets,” said Zhao. “Furthermore, if these planets do exist, they are likely to have similar compositions to our very own Earth given the similarity in Alpha Cen A/B and our beloved Sun.”

At present, there are no instruments that have been able to confirm the existence of any exoplanets in Alpha Centauri. But as Zhao indicated, her and her teammates are optimistic that future surveys will have the necessary sensitivity to do it:

“[T]his very month has seen the commissioning of several next-generation instruments promising the precision necessary to discover these possible planets in the near future, and this analysis has shown that it is for sure worth it to keep looking!”

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

These include the ESO-built Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) – which was recently installed at the Paranal Observatory – and the EXtreme PREcision Spectrometer (EXPRES) built at Yale University. This latter instrument is currently conducting an observation run at the Lowell Observatory in Arizona, which Zhao is participating in.

“These instruments are promising a precision of down to 10-30 cm/s and should be able to detect many more smaller, and further away planets – such as habitable planets around the Centauri stars,” said Zhao. “The field of view of these two instruments are slightly different (ESPRESSO has the southern hemisphere, where Alpha Centauri is, while EXPRES covers the northern hemisphere, for instance where the Kepler and many of the K2 fields are).”

With new instruments at their disposal, and methods like the one Zhao and her team developed, the closest star system to Earth is sure to become a veritable treasure trove for astronomers and exoplanet-hunters in the coming years. And anything we find there will surely become targets for direct studies by groups like Project Blue and Breakthrough Starshot. If ET resides next door, we’re sure to hear about it soon!

Further Reading: Yale News, The Astronomical Journal

Posted on by Matt Williams

Red Dwarf Star, Planet Orbiting at Right Angles. Mayhem.

Artist's impression of vessels floating near GJ436 its exoplanet, which orbits its star from pole to pole. Credit: University of Geneva/Denis Bajram

When we think of other planetary systems, we tend to think that they will operate by the same basic rules as our own. In the Solar System, the planets orbit close to the equatorial plane of the Sun – meaning around its equator. The Sun’s rotational axis, the direction of its poles based to its rotation, is also the same as most of the planets’ (the exception being Uranus, which rotates on its side).

But if the study of extra-solar planets has taught us anything, it is that the Universe is full of possibilities. Consider the star known as GJ436, a red dwarf located about 33 light-years from Earth. For years, astronomers have known that this star has a planet that behaves very much like a comet. But according to a recent study led by astronomers from the University of Geneva (UNIGE), this planet also has a very peculiar orbit.

The study, titled “Orbital Misalignment of the Neptune-mass Exoplanet GJ 436b With the Spin of its Cool Star“, recently appeared in the scientific journal Nature. The study was led by Vincent Bourrier of the Geneva University Observatory, and included members from the University of Grenoble Alpes, Tennessee State University, and the Center for Space and Habitability at the University of Bern.

Artist’s concept of the Neptune-sized planet Gliese 436b, surrounded by an envelop of hydrogen gas. Credit: NASA/ESA/STScI/G. Bacon

GJ436 has already been the source of much scientific interest, thanks in part to the discovery that its only confirmed exoplanet has a gaseous envelop similar a comet. This exoplanet, known as GJ436b, was first observed in 2004 using radial velocity measurements taken by the Keck Observatory. In 2007, GJ436b became the first Neptune-sized planet known to be orbiting very closely to its star (aka. a “Hot Neptune”).

And in 2015, GJ436 b made headlines again when scientists reported that its atmosphere was evaporating, resulting in a giant cloud around the planet and a long, trailing tale. This cloud was found to be the result of hydrogen in the planet’s atmosphere evaporating, thanks to the extreme radiation coming from its star. This never-before-seen phenomena essentially means that GJ436 b looks like a comet.

Another interesting fact about this planet is its orbital inclination, which astronomers have puzzled over for the past 10 years. Unlike the planets of the Solar System – whose orbits are largely circular – GJ436b follows a very eccentric, elliptical path. And as the research team indicated in their study, the planet also doesn’t orbit along the star’s equatorial plane, but passes almost above the its poles.

As Vincent Bourrier – a researcher at the Department of Astronomy of the UNIGE Faculty of Science, a member of the European Research Council project FOUR ACES, and the lead author of the study – explained in a UNIGE press release:

“This planet is under enormous tidal forces because it is incredibly close to its star, barely 3% of the Earth-Sun distance. The star is a red dwarf whose lifespan is very long, the tidal forces it induces should have since circularized the orbit of the planet, but this is not the case!”

Artist’s impression of JG436b, a hot Neptune located about 33 light years from Earth. Credit: Courtesy Space Telescope Science Institute

This was an especially interesting find for many reasons. On the one hand, it is the first instance where a planet was found to have a polar orbit. On the other, studying how planets orbit around a star is a great way to learn more about how that system formed and evolved. For instance, if a planet has been disturbed by the passage of a nearby star, or is being influenced by the presence of other massive planets, that will be apparent from its orbit.

As Christophe Lovis, a UNIGE researcher and co-author of the study, explained:

“Even if we have already seen misaligned planetary orbits, we do not necessarily understand their origin, especially since here it is the first time we measure the architecture of a planetary system around a red dwarf.”

Hervé Beust, an astronomer from the University of Grenobles Alpes, was responsible for doing the orbital calculations on GJ436b. As he indicated, the likeliest explanation for GJ436b’s orbit is the existence of a more massive and more distant planet in the system. While this planet is not currently known, this could be the first indication that GJ436 is a multi-planet system.

“If that is true, then our calculations indicate that not only would the planet not move along a circle around the star, as we’ve known for 10 years, but it should also be on a highly inclined orbit,” he said. “That’s exactly what we just measured!”

Artist impression of what GJ436b might look like. Credit: NASA

Another interesting takeaway from this study was the prediction that the planet has not always orbited so closely to its star. Based on their calculations, the team hypothesizes that the GJ436b may have migrated over time to become a “evaporating planet” that it is today. Here too, the existence of an as-yet-undetected companion is believed to be the most likely cause.

As with all exoplanet studies, these findings have implications for our understanding of the Solar System as well. Looking ahead, the team hopes to conduct further studies of this system in the hopes of determining if there is an elusive planetary companion to be found. These surveys will likely benefit from the deployment of next-generation missions, particularly the James Webb Space Telescope (JWST).

As Bourier indicated, “Our next goal is to identify the mysterious planet that has upset this planetary system.” Locating it will be yet another indirect way in which astronomers discover exoplanets – determining the presence of other planets based on orbital inclination of already discovered ones. The orbital inclination method, perhaps?

Further Reading: University of Geneva, Nature