Artist's depiction of TESS. Image Credit: TESS team.
Last week I held an interview with Dr. Sara Seager – a lead astronomer who has contributed vastly to the field of exoplanet characterization. The condensed interview may be found here. Toward the end of our interview we had a lengthy conversation regarding the future of exoplanet research. I quickly realized that this subject should be an article in itself.
The following is a list of approved missions that will continue the search for habitable worlds, with input from Dr. Seager about their potential for finding planets that might harbor life.
Transiting Exoplanet Survey Satellite (TESS)
Slated to launch in 2017, TESS will search for exoplanets by looking for faint dips in brightness as the unseen planet passes in front of its host star. With a price tag of $200 million, TESS will be the first space-based mission to scan the entire sky for exoplanets.
While the Kepler space telescope confirmed hundreds of exoplanets (with thousands of candidates yet to be confirmed) it stared 3000-light-years deep into a single patch of sky. TESS will scan hundreds of thousands of the brightest and closest stars in our galactic neighborhood.
“TESS will find many planets,” explained Seager in our interview. “The ones we’re highlighting it will find are rocky planets transiting small stars.” One of the missions goals is to find earth-like exoplanets in the habitable zone – the band around a star where water can exist in its liquid state.
The team hopes that TESS will find up to 1000 exoplanets in the first two years of searching. This will give astronomers a wealth of new worlds to study in more detail.
While the stars Kepler examined were faint and difficult to study in follow-up observations, the stars TESS will focus on are bright and close to home. These stars will be prime targets for further scrutiny with other space based telescopes.
“We plan to have a pool of planets, maybe a handful of them, that we can follow up with the James Webb Space Telescope … which will look at the atmospheres of those transiting planets, looking for signs of life,” Seager said.
ExoplanetSat
While slightly under the radar, ExoplanetSat will monitor bright stars using nano-satellites. Each nano-satellite will be capable of monitoring a single, bright, sun-like star for two years.
The current design of ExoplanetSat. The telescope is approximately the size of a loaf of bread. Image Credit: Pong et al. 2010 (SPIE 7731).
“The way that we describe this mission is not that we will find earth,” Seager said. “But if there is a transiting earth-like planet around a bright sun-like star, we will find it.”
Currently no planned mission has the capability to survey the brightest stars in the sky. TESS will observe stars of magnitude 5 through 12 – the dimmest our eyes can see and fainter.
The brightest stars are too widely spaced for a single telescope to continuously monitor. The best method is to monitor the brightest sun-like stars in a targeted star search instead.
The mission is pretty far along in terms of funding. It has already received a few million dollars and is about one million short of launching the first prototype.
After a successful demonstration the goal is to launch a fleet of nano-satellites to observe enough bright stars to find a number of interesting exoplanets. One day we may be able to look at a bright star in our night sky and know it has a planet.
Direct Imaging Missions
Disentangling a faint, barely reflective, exoplanet from its overwhelmingly bright host star in a direct image seems nearly impossible. A common analogy is looking for a firefly next to a searchlight across North America. Needless to say, very few exoplanets have been seen directly.
Because of the difficulties NASA is fostering a study and soliciting applications with a single goal in mind: create a mission that will directly image exoplanets under a price cap of one billion dollars.
Seager is working with a team that plans to utilize a star shade – “a specially shaped screen that will fly far from the telescope and block out the light from the star so precisely that we will see any planets like earth.”
The shade isn’t circular but shaped like a flower. Light waves would bend around a circle and create spots brighter than the planets themselves. The flower-like shape avoids this while blocking out the starlight – making a planet that is one ten billionth as bright as its host star visible.
The star shade and the telescope have to be aligned perfectly at 125,000 miles away. Once aligned, the system will observe a distant star, and then move to another distant star and re-align. This is technologically speaking, unchartered territory.
While this mission may not occur in full tomorrow, or even years from tomorrow, astronomers’ synapses are firing. We’re coming up with new techniques that will advance technology and find earth-like worlds.
Etc.
Above is a list of only a handful of future exoplanet missions – all at various stages in their production – with some still on the drawing board and others having received full funding and preparing for launch. With creativity and advancing technology we’ll detect a true-earth analogue in the near future.
This illustration compares our Earth with the newly confirmed lava planet Kepler-78b. Kepler-78b is about 20 percent larger than Earth, with a diameter of 9,200 miles, and weighs roughly 1.8 times as much as Earth.
David A. Aguilar (CfA)
A newly verified planet found in data from the Kepler mission delivers on the space telescope’s task of finding Earth-size planets around other stars. The new planet, called Kepler-78b, is the first Earth-sized exoplanet discovered that has a rocky composition like that of Earth. Similarities to Earth, however, end there. Kepler-78b whizzes around its host star every 8.5 hours at a distance of about 1.5 million kilometers, making it a blazing inferno and not suitable for life as we know it.
“We’ve been hearing about the sungrazing Comet ISON that will go very close to the Sun next month,” said Andrew Howard, of the University of Hawaii at Manoa’s Institute for Astronomy. “Comet ISON will approach the Sun about the same distance that Kepler-78b orbits its star, so this planet spends its entire life as a sungrazer.”
Howard is the lead author on one of two papers published in Nature that details the discovery of the new planet. He spoke during a media webcast discussing the finding.
“This is a planet that exists but shouldn’t,” added astronomer David Latham of the Harvard-Smithsonian Center for Astrophysics (CfA), also discussing the discovery during the webcast.
Kepler-78b is 1.2 times the size of Earth with a diameter of 14,800 km (9,200 miles) and 1.7 times more massive. As a result, astronomers say it has a density similar to Earth’s, which suggests an Earth-like composition of iron and rock. A handful of planets the size or mass of Earth have been discovered, but Kepler-78b is the first to have both a measured mass and size. With both quantities known, scientists can calculate a density and determine what the planet is made of.
Its star is slightly smaller and less massive than the sun and is located about 400 light-years from Earth in the constellation Cygnus.
However, the close-in orbit of Kepler-78b poses a challenge to theorists. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there. Back when this planetary system was forming, the young star was larger than it is now. As a result, the current orbit of Kepler-78b would have been inside the swollen star.
This diagram illustrates the tight orbit of Kepler-78b, which orbits its star every 8.5 hours at a distance of less than a million miles. It is only 2.7 stellar radii from the center of the star, or 1.7 stellar radii from the star’s surface. David A. Aguilar (CfA)
“It couldn’t have formed in place because you can’t form a planet inside a star,” said team member Dimitar Sasselov, also from CfA. “It couldn’t have formed further out and migrated inward, because it would have migrated all the way into the star. This planet is an enigma.”
One idea, suggested Howard, is that the planet is the remnant core of a former gas giant planet, but that turns out to be a problem as well. “We just don’t know what the origin of this planet is,” Howard said.
However, the two teams of planet hunters feel that its existence bodes well for future discoveries of habitable planets.
The two independent research teams used ground-based telescopes for follow-up observations to confirm and characterize Kepler-78b. The team led by Howard used the W. M. Keck Observatory atop Mauna Kea in Hawaii. The other team led by Francesco Pepe from the University of Geneva, Switzerland, did their ground-based work at the Roque de los Muchachos Observatory on La Palma in the Canary Islands.
To determine the planet’s mass, the teams employed the radial velocity method to measure how much the gravitation tug of an orbiting planet causes its star to wobble. Kepler, on the other hand, determines the size or radius of a planet by the amount of starlight blocked when it passes in front of its host star.
“Determining mass of an Earth-sized planet is technically daunting,” Howard said during the webcast, explaining how they used the HIRES (High Resolution Echelle Spectrometer) on Keck. “We pushed HIRES to its limit. The observations were difficult because the star is young with many more star spots (just like sunspots on our Sun) than our Sun, and we have to remove them from our data. But since this planet orbits every eight and a half hours, we were able to watch an entire orbit in one night. We clearly saw the planet’s signal, and we watched it eight different nights.”
David Aguilar from CfA said both teams knew the other team was studying this star, but they didn’t compare their work until both teams were ready to submit their papers so that they wouldn’t influence each other. “It was very encouraging both teams got the same result,” Aguilar said.
Howard also thought having two separate teams work on the same target was great. “We didn’t have to wait for further confirmation of the planet, because the two teams confirmed each other,” he said. “In science, this is as good as it gets.”
Francesco Pepe from the second team said they benefitted from using a twin of the original HARPS (High Accuracy Radial velocity Planet Searcher) which has found nearly 200 exoplanets. “HARPS North at La Palma has the same precision and efficiency as its twin,” Pepe explained during the webcast, “and we decided to guarantee time to follow up on small exoplanet candidates from Kepler. We optimized our observing strategy and we expect many more confirmations in the coming years from this technique.”
As for Kepler-78b, this is a doomed world. Gravitational tides will continue to pull Kepler-78b even closer to its star. Eventually it will move so close that the star’s gravity will rip the world apart. Theorists predict that the planet will vanish within three billion years. Interestingly, astronomers say, our solar system could have held a planet like Kepler-78b. If it had, the planet would have been destroyed long ago leaving no signs for astronomers today.
“We did not detect additional planets in this system,” said Howard, “but we hope to observe this system more in the future.”
Planetary Scientist Sara Seager. Image courtesy MIT.
Astronomers have now discovered one thousand extrasolar planets, reaching a milestone in modern astronomy. (See a recent Universe Today article on the subject.) While many have contributed to this achievement, Dr. Sara Seager of MIT has played a large role over the past two decades by contributing vastly to the field of exoplanet characterization. Her theoretical work led to the first detection of an exoplanet atmosphere.
The following is a condensed interview I held with Seager earlier this week.
What first pulled you in to the field of astronomy?
When I was 10 I got to see a really dark sky (well outside her hometown of Toronto, Canada). I stepped out in the middle of the night and I just saw so many stars. I wish you and everyone could see that. So many stars, I just couldn’t believe it.
You were working at Harvard for your PhD in the mid ‘90s when we first detected exoplanets. What was that like?
The mood was quite different. Today everybody wants to talk about it (exoplanets) and write about it. There’s a lot of hype. But back then it was very quiet.
There was a huge amount of skepticism too. People don’t like change. I want you to imagine a world where the gas giants like Jupiter and Saturn are very far from the star and the terrestrial planets like Earth, Mercury, Venus, and Mars are very close to the star. People had constructed theories on how planetary bodies form based on that one example.
So when the first planets around sun-like stars were found, they were Jupiter-mass planets, but they were several times closer to their star than Mercury is to our Sun. It offended all thoughts, theories, and paradigms … As scientists we’re supposed to be skeptical and push back on new discoveries and theories that are upsetting the system. There was huge skepticism.
An exoplanet seen from its moon (artist’s impression). Via the IAU.
How difficult was it during this time to work on exoplanets?
Many people, including my graduate student peers and faculty said, “Why are you doing this (working on exoplanet research)? This is not going to happen. And even if exoplanets are real we’re never going to be able to study their atmospheres,” which is what my PhD was on.
What pushed you through despite all the skepticism?
Ironically, I was not committed to a career in science. I didn’t feel like I needed to be involved with something that was at the 100 percent certainty level. I was free because I didn’t have a plan. I had nothing to lose by doing something I thought was really cool and exciting.
When you’re doing a PhD you’re really learning how to answer a tough question. Usually if you do a homework set in high school, or college, there’s already a known answer. But when you’re doing a PhD, if you’re asking a really hard question that has never been asked before you’re answering that question with your own tools that you’ve developed yourself.
At that time, I knew… the real thing is not just what you’re working on but it’s the tools that you’re using and the things that you’re learning. At the end of the day if you don’t stay in science you have gained a skill that most people don’t have.
Artist concept of an exoplanet. Credit: David A. Hardy. What changed then? What kept you in science after graduate school?
I had freedom and really enjoyed what I was doing.
What is your motivation for studying exoplanets? Why should we study exoplanets?
We want to know: Are we alone? We want to know if there is life beyond earth. Eventually we will have dozens to hundreds of potential earth-like planets to study in detail. We want to look at their atmospheres for signs of life by way of biosignature gases.
What do you think is the likelihood that we will discover an earth-like planet orbiting a sun-like star?
Well, it really just depends if we can rally resources and interest in doing this problem. We think we know how to find an earth-like planet around a sun-like star. But it’s a very very very hard endeavor. We think that the earths are out there. It’s just a matter of building the sophisticated space telescopes that we need.
So what are the chances? It’s really more of a political and economical question more than anything else. I think it’s inevitable that eventually we will find one.
Do you have a favorite planet?
I always like to say my favorite planet is the next planet. We have a sort of ADD (attention deficit disorder) in this field where we’re propelled and motivated forward by finding the next exciting planet. Artist’s impression of exoplanets around other stars. Credits: ESA/AOES Medialab We’ve reached a huge milestone in astronomy of detecting one thousand exoplanets. What does this milestone mean to you?
There’s a caveat here, an uncertainty. We don’t know which one is going to be number one thousand because we don’t agree on the definition of a planet. And even if we did, there’s an uncertainty in the mass and size measurements such that some objects that are called planets probably aren’t planets depending on what definition you want. Occasionally a planet is retracted.
But in general, we’re about to pass the one thousandth mark. What do I think? I think it’s phenomenal. I mean I’m so excited.
The study of exoplanets really started as a field where no one wanted to work on it. People thought it was never going to happen, they thought even if there were real planets we’d never get any measurements beyond stamp collecting – a derogatory phrase we sometimes use in astronomy for science that is not that useful. You just find discoveries and they pile up because you don’t know what to do with them.
We’ve changed the paradigm of planet formation, found exotic types of planets, and we’re right on our way to finding another Earth. So I think it couldn’t be better.
More than 1,000 exoplanets have been confirmed and cataloged (PHL @ UPR Arecibo)
It was just last week that we reported on the oh-so-close approach to 1,000 confirmed exoplanets discovered thus far, and now it’s official: the Extrasolar Planets Encyclopedia now includes more than 1,000! (1,010, to be exact.)
21 years after the first planets beyond our own Solar System were even confirmed to exist, it’s quite a milestone!
The milestone of 1,000 confirmed exoplanets was surpassed on October 22, 2013 after twenty-one years of discoveries. The long-established and well-known Extrasolar Planets Encyclopedia now lists 1,010 confirmed exoplanets.
Not all current exoplanet catalogs list the same numbers as this depends on their particular criteria. For example, the more recent NASA Exoplanet Archive lists just 919. Nevertheless, over 3,500 exoplanet candidates are waiting for confirmation.
The first confirmed exoplanets were discovered by the Arecibo Observatory in 1992. Two small planets were found around the remnants of a supernova explosion known as a pulsar. They were the surviving cores of former planets or newly formed bodies from the ashes of a dead star. This was followed by the discovery of exoplanets around sun-like stars in 1995 and the beginning of a new era of exoplanet hunting.
A “Periodic Table of Exoplanets” as listed by the Extrasolar Planets Encyclopedia (PHL)
(The first exoplanets to be confirmed were two orbiting pulsar PSR B1257+12, 1,000 light-years away. A third was found in 2007.)
Exoplanet discoveries have been full of surprises from the outset. Nobody expected exoplanets around the remnants of a dead star (i.e. PSR 1257+12), nor Jupiter-size orbiting close to their stars (i.e. 51 Pegasi). We also know today of stellar systems packed with exoplanets (i.e. Kepler-11), around binary stars (i.e. Kepler-16), and with many potentially habitable exoplanets (i.e. Gliese 667C).
“The discovery of many worlds around others stars is a great achievement of science and technology. The work of scientists and engineers from many countries were necessary to achieve this difficult milestone. However, one thousand exoplanets in two decades is still a small fraction of those expected from the billions of stars in our galaxy. The next big goal is to better understand their properties, while detecting many new ones.”
– Prof. Abel Mendéz, Associate Professor of Physics and Astrobiology, UPR Arecibo
Source: Press release by Professor Abel Méndez at the Planetary Habitability Laboratory (PHL) at Arecibo
While not illustrating the full 1,010 lineup, this is still a mesmerizing visualization by Daniel Fabrycky of 885 planetary candidates in 361 systems as found by the Kepler mission. (I for one am looking forward to the third installment!)
Of course, scientists are still hunting for the “Holy Grail” of extrasolar planets: an Earth-sized, rocky world orbiting a Sun-like star within its habitable zone. But with new discoveries and confirmations happening almost every week, it’s now only a matter of time. Read more in this recent article by Universe Today writer David Dickinson.
Artist's conception of Kepler-56, which has two planets orbiting at a tilt to their star despite the fact that scientists found no bigger gas giant planet to alter their orbits. Credit: Daniel Huber/NASA's Ames Research Center.
A faraway group of planets is puzzling scientists. Newly reported Kepler-56’s system has three planets — two smaller ones close by, and a much larger one further out. The inner planets are orbiting at a tilt to the equator of the host star.
Scientists have seen that tilt before in other systems, but they thought you would need a “hot Jupiter” — a huge gas giant planet close to the star — to make that happen. Here, that’s not the case. The outer planet’s gravity, distant as it is, is pulling the two planets into their tilted orbits.
“This is a very puzzling result that is sure to challenge our understanding of how solar systems form,” stated co-author Tim Bedding, a physics researcher at the University of Sydney.
Kepler-56 is 3,000 light-years away from Earth and has a mass about 30% greater than that of our Sun. As the name implies, astronomers used the Kepler space telescope to make the discovery.
Planets everywhere. So where are all the aliens? Credit: ESO/M. Kornmesser
A quiet milestone in modern astronomy may soon come to pass. As of today, The Extrasolar Planets Encyclopedia lists a current tally of 998 extrasolar planets across 759 planetary systems. And although various tabulations differ slightly, very soon we should be living in an era where over one thousand exoplanets are known.
The history of exoplanet discovery has paralleled the course of the modern age of astronomy. It’s strange to think that a generation has already grown up over the past two decades in a world where knowledge of extrasolar planets is a given. I remember hearing of the promise of such detections growing up in the 1970’s, as astronomers put the odds at detection of planets beyond our solar system in our lifetime at around 50%.
A “Periodic Table of Exoplanets” Credit: PHL @ UPR Arecibo.
Sure, there were plenty of false positives long before the first true discovery was made. 70 Ophiuchi was the site of many claims, starting with that of W.S. Jacob of the Madras Observatory way back in 1855. The high proper motion exhibited by Barnard’s Star at six light years distant was also highly scrutinized throughout the 20th century for claims of an unseen companion causing it to wobble. Ironically, Barnard’s Star still hasn’t made it into the pantheon of stars boasting planetary worlds.
A portrait of the HR8799 planetary system as imaged by the Hale Telescope. (Credit: NASA/JPL-Caltech/Palomar Observatory).
But the first verified claim of an exoplanetary system came from a bizarre and unexpected source: a pulsar known as PSR B1257+12, which was discovered to host two worlds in 1992. This was followed by the first discovery of a world orbiting a main sequence star, 51 Pegasi in 1994. I still remember getting my hands on the latest issue of Astronomy magazine— we got our news, often months later, from actual paper magazines in those days —announcing “Planet Discovered!” on the cover.
Most methods and techniques used to discover exoplanets rely on either radial velocity or dips in the light output of a star from a transiting world. Both have their utility and drawbacks. Radial velocity looks for shifts in the star’s spectra as an unseen companion tugs it around a common center of mass. Though effective, it can only place a lower limit on the planet’s mass… and it’s biased towards worlds in short orbits. This is one reason that “hot Jupiters” have dominated the early exoplanet catalog: we hadn’t been looking for all that long.
Another method famously employed by surveys such as the Kepler space telescope is the transit detection method. This allows a much more refined estimate of a planet’s mass and orbit, assuming it transits the disk of its host star as seen from our Earthly vantage point in the first place, which most don’t.
A size comparision of exoplanets versus composition. (Credit: Marc Kuchner/NASA/GSFC).
Direct detection via occulting the host star is also coming of age. One of the first exoplanets directly imaged was Fomalhaut b, which can be seen changing positions in its orbit from 2004 to 2006.
Gravitational microlensing has also bared planetary fruit, with surveys such as MOA (Microlensing Observations in Astrophysics) and OGLE (the Optical Gravitational Lensing Experiment) catching brief lensing events as an unseen body passes in front of a background star. Distant free-ranging rogue planets can only be detected via this method.
More exotic techniques also exist, such as relativistic beaming (sounding like something out of Star Trek). Other methods include searches for tiny light variations as an illuminated planet orbits its host star, deformities caused by ellipsoidal variations as massive planets orbit a star, and infrared detections of circumstellar disks. We’re always amazed at the wealth of data that can be teased out of a few dim photons of light.
A scatter plot of exoplanet discoveries as of 2010 displaying mass versus semi-major axis. Select exoplanets are labeled. A majority were detected via radial velocity (blue) and the transiting method (green). The remainder were detected by other methods (click here for a full description). Graph in the Public Domain.
Universe Today has grown up with exoplanet science, from reporting on the hottest, fastest, and other notable “firsts”. A bizarre menagerie of worlds are now known, many of which defy the imagination of science fiction writers of yore. Want a world made of diamond, or one where it rains glass? There’s now an “exoplanet for that”.
Exoplanet news has almost gone from the incredible to the routine, as Tatooine-like worlds orbiting binary stars and systems with worlds in bizarre resonances are announced with increasing frequency.
Exoplanet surveys also have a capacity to peg down that key fp factor in the famous Drake equation, which asks us “what fraction of stars have planets”. It’s been long suspected that stars with planets are the rule rather than the exception, and we’re just now getting hard data to back that assertion up.
Missions, such as NASA’s Kepler space telescope and CNES/ESA CoRoT space telescope have swollen the ranks of extrasolar worlds. Kepler recently ended its career staring off in the direction of the constellations Cygnus, Hercules and Lyra and still has over 3,200 detections awaiting confirmation.
Exoplanet discoveries by year as of October 2013, color coded by method. Blue=radial velocity, Green=transiting, Yellow=timing, Red=direct imaging, Orange=microlensing
But is a given world Earthlike, or just Earth-sized? That’s the Holy Grail of modern exoplanet detection: an Earth-sized world orbiting in a star’s habitable zone. We’re cautious every time the latest “Earth-twin” makes its way into the headlines. From the perspective of an intergalactic astronomer, Venus in our own solar system might appear to fit the bill, though I wouldn’t bank the construction of an interstellar ark on it and head there just yet.
Exoplanet science has definitely come of age, allowing us to finally begin characterization of solar systems and give us some insight into solar system formation.
But perhaps what will be the most enduring legacy is what the discovery of extrasolar planets tells us about ourselves. How common (or rare) is the Earth? How typical is the story of our solar system? If the “first 1,000” are any indication, we strongly suspect that terrestrial planets come in enough distinct varieties or ”flavors” to make Baskin Robbins envious.
And the future of exoplanet science looks bright indeed. One proposed mission, known as the Fast INfrared Exoplanet Spectroscopy Survey Explorer, or FINESSE, would target exoplanet atmospheres, if given the go ahead for a 2017 launch. Another proposal, known as the Wide Field Infrared Survey Telescope, or WFIRST, would search for microlensing events starting in 2023. A mission that scientists would love to fly that always seems to be shelved is known as the Terrestrial Planet Finder.
But the exoplanet hunting mission that’s closest to launch is the Transiting Exoplanet Survey Satellite, or TESS. Unlike Kepler, which stares at a single patch of sky, TESS will be an all-sky survey looking at a half million stars.
We’re also just approaching an era where spectroscopy may allow us to detect exomoons and the chemistry taking place on these far off exoworlds. An example of an exciting discovery would be the detection of a chemical such as chlorophyll, a chemical that we know on Earth only exists as the result of life. But what a tantalizing discovery a blip on a graph would be, when what we humans really want to see is the vista of those far-flung alien forests!
Such is the exciting era we live in. Congratulations, humanity, on detecting 1,000 exoplanets… here’s to a thousand more!
Artist's impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Credit: Mark A. Garlick, space-art.co.uk, University of Warwick and University of Cambridge
Remains of a water-filled asteroid are circling a dying white dwarf star, right now, about 150 light-years from us. The new find is the first demonstration of water and a rocky surface in a spot beyond the solar system, researchers say.
The discovery is exciting to the astronomical team because, according to them, it’s likely that water on Earth came from asteroids, comets and other small bodies in the solar system. Finding a watery rocky body demonstrates that this theory has legs, they said. (There are, however, multiple explanations for water on Earth.)
“The finding of water in a large asteroid means the building blocks of habitable planets existed – and maybe still exist – in the GD 61 system, and likely also around substantial number of similar parent stars,” stated lead author Jay Farihi, from Cambridge’s Institute of Astronomy.
Earth’s oxygen and water as detected by Venus Express (ESA)
“These water-rich building blocks, and the terrestrial planets they build, may in fact be common – a system cannot create things as big as asteroids and avoid building planets, and GD 61 had the ingredients to deliver lots of water to their surfaces. Our results demonstrate that there was definitely potential for habitable planets in this exoplanetary system.”
More intriguing, however, is researchers found this evidence in a star system that is near the end of its life. So the team is framing this as a “look into our future”, when the Sun evolves into a white dwarf .
The water likely came from a “minor planet” that was at least 56 miles (90 kilometers) in diameter. Its debris was pulled into the atmosphere of the star, which was then examined by spectroscopy. This study revealed the ingredients of rocks inside the star, including magnesium, silicon and iron. Researchers then compared these elements to how abundant oxygen was, and found that there was in fact more oxygen than expected.
White Dwarf Star
“This oxygen excess can be carried by either water or carbon, and in this star there is virtually no carbon – indicating there must have been substantial water,” stated co-author Boris Gänsicke, from the University of Warwick.
“This also rules out comets, which are rich in both water and carbon compounds, so we knew we were looking at a rocky asteroid with substantial water content – perhaps in the form of subsurface ice – like the asteroids we know in our solar system such as Ceres.”
The measurements were obtained in ultraviolet with the Hubble Space Telescope’s cosmic origins spectrograph. What’s more, the researchers suspect there are giant exoplanets in the area because it would take a huge push to move this object from the asteroid belt — a push that most likely came from big planet.
“This supports the idea that the star originally had a full complement of terrestrial planets, and probably gas giant planets, orbiting it – a complex system similar to our own,” Farihi added.
As far as our understanding of life in the Universe goes, right now, we’re it. But the past decade has brought discoveries of hundreds of planets orbiting other stars, some of which could potentially host life. Fellow science journalist Lee Billings has written a new book about the exciting field of searching for extrasolar planets. Five Billion Years of Solitude (read our review here) takes a look at some of the remarkable scientists and the incredible discoveries being made.
Earlier this week, we talked with Lee about the book and the future of how we might find a mirror of Earth.
Universe Today: What was the impetus behind writing this book – was there a specific event or moment where you said, ‘I want to write about astrobiology and the search for exoplanets,’ or was it a more gradual thing over time, where you were just intrigued by the whole expanding field?
Lee Billings
Lee Billings: A little bit of both. I was definitely intrigued by the expanding field of searching for exoplanets, but it came all together for me after interviewing astronomer Greg Laughlin from the University of California, Santa Cruz in 2007 for an infographic about exoplanets. Near the end of our conversation, he mentioned — rather off the cuff — that if you tracked the smallest exoplanets found year by year and graphed them out over time, the trend-line would indicate that we would find an Earth-sized exoplanet by 2011. And I thought, “Holy crap, that’s just four years away!”
I was struck by the disconnect where we could see this plain-as-day data, but the wider world didn’t realize or appreciate this. It also bothered me that we’d soon be finding potentially habitable other worlds, and yet have great difficulty actually determining if they were habitable or even inhabited. And so there was this observational disconnect too, and a lot of people who didn’t seem to care there was this disconnect.
UT: And now that finding exoplanets has made front page news, are you encouraged by how people from afar are viewing this field?
LB: Yes and no. Exoplanets have been in the news for years now. 10 to 15 years ago when astronomers like Geoff Marcy and Michel Mayor were finding the first exoplanets — honkin’ huge balls of gas orbiting close to their stars — it would make front page news. Right now, there’s kind of been ‘exoplanet fatigue,’ where every couple of days a new exoplanet is being announced and exoplanets are even less in the news now because of this overload. And it’s going to keep happening, and I feel like by 2020 finding an Earth-sized planet in the habitable zone isn’t going to make front-page news because it’s going to be happening all the time and people are getting used to it.
UT: Kind of like the Apollo program all over again, where people soon got tired of watching people walk on the Moon?
LB: Yes! Even though I feel like more people in the public are aware of exoplanets being discovered and they even think exoplanets are cool, many think that finding thousands of exoplanets is just like stamp collecting — oh, we found another planet, let’s put it in the book and isn’t that one really pretty — that’s not what this is about. It’s about finding signs of life, finding a sense of context for ourselves in the wider universe, figuring out where Earth and all life upon it fits in this greater picture. I don’t think people are attuned to that side, but are being seduced by the stamp-collecting, horse-race nature of how finding exoplanets are depicted in the media. The emphasis isn’t on what it is going to take to really go out and find out more details about these exoplanets.
Frank Drake and the Drake Equation,
UT: You had the opportunity to talk with some of the great minds of our time — of course, Frank Drake is just such an icon of SETI and the potential for finding life out there in the Universe. But I think one of the most amazing things in your book that I’d never heard of before comes in one of the first chapters where you’re talking with Frank Drake and his idea for a spacecraft that uses the Sun as a gravitational lens to be able to see distant planets incredible detail. That’s amazing!
LB: If you use the Sun as a gravitational lens as sort of an ultimate telescope is really fascinating. As Drake said in the book, you can get some mind-boggling, insane data if you used the Sun as a gravitational lens, and align that with another gravitational lens in the Alpha Centauri system and you can send a high bandwidth radio signal in between those two stars with just the power of a cell phone. In visible light, you could possibly see things on a nearby exoplanet like night-time lighting, the boundary between land and sea, clouds, and weather patterns. It just boggles the mind.
There are other techniques out there that could in theory deliver these sorts of similar observations, but there’s just kind of a technical sweetness to the notion that the stars themselves could be the ultimate telescopes that we use to explore the universe and understand our place in it. I think that’s kind of a wild, poetic and elegant idea.
UT: Wow, that is so compelling. And speaking of compelling, can you talk about Sara Seager and the time you were able to spend with her, getting to know her and her work? Her story is quite compelling not to mention heartbreaking.
LB: She’s a remarkable woman and a brilliant scientist and I feel deeply privileged and honored to be able to tell her story — and that she shared so many details of her personal story with me. Really, she’s kind of a microcosm of the field at large. She crossed over from what she originally studied — from cosmology to exoplanetolgy — and her career seems to be defined by the refusal to accept that certain things might be impossible. She is always pushing the envelope and just keeps her eyes on the prize, so to speak, of finding smaller more Earth-like planets that could be habitable and finding ways of determining what they are actually like. There’s a parallel there between her path and astronomy at large, where there is tension between parts of the professional community. A lot of astronomy is concerned with studying how the universe began and the ancient, the distant, the dead. Exoplanetology is more concerned with the nearest stars to Earth and the planets — the new, the nearby and the living. I feel like she represents that shift and embodies some of that tension.
There’s also an element of tragedy, where she suffered a significant loss with the death of her husband, and had to find a way to get through it and get stronger coming out on the other side. I see similarities between that and what has happened in the field at large where we’ve seen big federally funded plans for future, next-generation telescopes like the Terrestrial Planet Finder, be scuttled on the rocky reefs of politics — and other things. It’s complicated why that’s happened, but there’s no denying that is HAS happened. 15 years ago we were talking about launching TPS by 2014 and now here we are, almost to 2014 and the James Webb telescope isn’t even launched and its eating up all the money for everything else. And now the notion of doing these big kinds of life-finding missions have fallen by the wayside. There’s been kind of the death of a dream, and the bright future that was forecast for what was going to happen for exoplanets doesn’t seem like it’s going to be. The community has had to respond to that and rebuild from that, and there doesn’t seem to be a lot of unity on what the best path forward is.
And also, Sara Seager is walking the line between the old way of big, federally funded projects and a new private, philanthropic path that may or may not be sustainable or successful, but it’s different and trying to do science in a new way. So maybe we don’t need to rely on big government or NASA to do this. Maybe we could ask philanthropists or crowd-funding or new enterprises that could help finance the projects in going forward. She’s got her feet in both worlds and is emblematic of the field right now.
Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.
UT: Yes, as you mention in the book, there is this tragic possibility that we may never find the things that these scientists are searching for — “mirror Earths, alien life, extraterrestrial intelligence, or a future beyond our lonely, isolated planet.” What do you see as the future of the search for exoplanets, in this age of funding cuts?
LB: What seems to be happening is that astronomers and planet hunters are needing to change their baselines and move their goalposts. In the past when people talked about space telescopes and finding signs of life, they were thinking of directly imaging planets around Sun-like stars and finding indications of life through studying the atmosphere and even surface features. The new way that is coming about and will likely happen in the next few decades, is an emphasis on smaller, cooler, less sun-like stars — the Red Dwarf or M-Dwarf stars. And it won’t be about directly imaging planets, but looking at transiting planets because it is easier to look at planets around lower-mass stars and at super-Earths that are easier to find and study. But these are rather alien places and we don’t know much about them, so it’s an exciting frontier.
But while transits are jackpots — in that you get all sorts of information like period, mass, radius, density and measures of the planet’s upper atmosphere — transits are very rare. If you think about the nearest thousand stars and if we are just looking for transits, that sort of search will only yield a fraction of the planets and the planetary diversity that exist. If you’re looking for life and potentially habitable planets, we really need a bigger sample and more than just transits to fill out the census of planets orbiting the stars around us.
I think missions like TESS and James Webb are going to be important, but I don’t think it will be enough. It will only leave us on the cusp of answering these bigger questions. I hope I’m wrong and that the emphasis on M-dwarfs and super-Earths and transits will be far more productive and surprising than anyone could have imagined or that there will be technology developed that are orders of magnitude cheaper, more affordable and better than these big telescopes.
But to answer the big questions more robustly in a way that is more satisfying to the public and data-hungry scientists, we’re probably going to have to make big investments, and invest the blood sweat and tears into building one of these big space telescopes. People in the astronomy community have been kicking and screaming about this because they realize the money just isn’t there.
But as someone once told me, there an economic inevitability to this in terms of how much the public can be engaged by these questions and how much they might hunger and thirst for finding other planets and life beyond our solar system. I feel like there is a strong push that could be made. I feel that the public would offer more support for these types of investments rather than for other projects, such as a a big space-based gravitational wave observatory or a big telescope devoted to studying dark energy.
Of course, we are living in this era of constrained and falling budgets, it’s going to be a really hard sell for any of these investments in astronomy, but pursuing the ancient, distant and dead instead of the new, nearby and living is probably a losing proposition, I do I wish astronomers the best of luck, but I hope they make the smart choice to prioritize the most publicly engaging science.
Artist’s impression of the transiting exoplanet HAT-P-7b. Credit: NASA/ESA
UT: You write about the competition and sometimes the disdain that competing astronomers have for each other. Is this competition good, or should there be more unity in the field?
LB: In the interest of the community at large, I’d have to say unity is better and that some people have to wait their turn or reduce their expectations. I’m biased; I’m an advocate of exoplanet missions and these investments. But this is publicly funded science and I think it’s important for the community to be unified because it’s all too easy for the bean-counters in Washington to hear the discordant cacophony coming from the various astronomer hatchlings in the nest, and that there is no consensus except they are hungry and they want more.
They need to be unified to withstand the anti-scientific trends in funding we are seeing in our federal government right now. On the other hand, competition is important. But when you are doing publicly funded science, the scientists need to do a good job of making their case of why they should be funded.
UT: What was the most memorable experience in writing this book?
LB: That’s a really hard question! One of my great privileges and joys of writing the book was having access to these scientists and their work. But one of the most memorable things was visiting California’s Lick Observatory on Mount Hamilton in 2012 for the Transit of Venus. It was the last transit of Venus in our lifetime and it was amazing to stand there and think that the last time the transit was visible from Mount Hamilton was a century before, and realize all the changes that had happened in astronomy since then. This transit happened slowly over hours and it was amazing to stand there and realize, this is the last time in your life you’re going to see it and to wonder what is going to happen in the intervening years until this event occurs again.
But Lick Observatory was an appropriate place to be since that’s where some of the first exoplanets were found. When the last Transit of Venus took place, we hadn’t walked on the Moon, there were no computers, and we’ve had all these great discoveries in astronomy. I was thinking about what the world will be like in another hundred years or so, and thinking how while that is a long time for us, in the scale of planetary time, it is nothing at all! The Sun won’t have significantly aged and Venus will likely look exactly the same in 2117 for the next transit, but I would guess the Earth will be very different then. It’s kind of indicative of this transitional era we’re in. It was a very poignant moment for me.
UT: It’s similar to how Frank Drake talked about how he and his colleagues thought that searching for radio emissions from other civilizations would be so important in the search for extraterrestrial intelligence, but realizing that Earth’s radio emissions from our technology is waning and only lasted a short period of time.
LB: Yeah, perhaps when people look back at my book in the future, they might say, ‘wow, this guy was so blinkered and stupid — he didn’t see this technologies X, Y and Z coming and didn’t see monumental discoveries A, B, and C coming.’ I kind of hope that’s actually the case, because it will mean the search for extraterrestrial life and intelligence will have surpassed my wildest dreams. However, I didn’t try to predict what was going to happen, but just wanted to capture this strange and seemingly unique moment in time in which we are poised on the threshold of these immense discoveries that could totally transform our conception of the Universe and our place in it.
UT: Talking to you today, we can obviously tell how passionate you are about this subject and you were the perfect person to write about it!
Artist's conception of PSO J318.5-22. Credit: MPIA/V. Ch. Quetz
The planetary world keeps getting stranger. Scientists have found free-floating planets — drifting alone, away from stars — before. But the “newborn” PSO J318.5-22 (only 12 million years old) shows properties similar to other young planets around young stars, even though there is no star nearby the planet.
“We have never before seen an object free-floating in space that that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone,” stated team leader Michael Liu, who is with the Institute for Astronomy at the University of Hawaii at Manoa. “I had often wondered if such solitary objects exist, and now we know they do.”
Image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium
The planet is about 80 light-years from Earth, which is quite close, and is part of a star group named after Beta Pictoris that also came together about 12 million years ago. There is a planet in orbit around Beta Pictoris itself, but PSO J318.5-22 has a lower mass and likely had a different formation scenario, the researchers said.
Astronomers uncovered the planet, which is six times the mass of Jupiter, while looking for brown dwarfs or “failed stars.” PSO J318.5-22’s ultra-red color stood apart from the other objects in the survey, astronomers said.
The free-floating planet was identified in the Pan-STARRS 1 wide-field survey telescope in Maui. Follow-up observations were performed with several other Hawaii-based telescopes, including the NASA Infrared Telescope Facility, the Gemini North Telescope, and the Canada-France-Hawaii Telescope.
The discovery will soon be detailed in Astrophysical Letters, but for now you can read the prepublished verison on Arxiv.
An artist's conception of two magnetic fields interacting in a bow shock. Image credit: NASA
Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.
Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.
An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.
When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.
Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.
Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.
As a bright star, HD 189733b has been studied extensively by astronomers. Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.
This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind. With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.
The bow shock leads the planet – causing the light to drop a little earlier than expected. The amount of light blocked by the bow shock, however, will change as the planet moves through a variable stellar wind. If the stellar wind is particularly strong, the resulting bow shock will be strong, and the transit depth will be greater. If the stellar wind is weak, the resulting bow shock will be weak, and the transit depth will be less.
The video below shows the light curve of a bow shock and exoplanet.
“We found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies,” Llama told Universe Today. “As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.”
While there were no transit observations for this study, this theoretical outlook demonstrates that it will be possible to detect the bow shock, and therefore the magnetic field, of a distant exoplanet. Dr. Llama comments: “This will help us to better identify potentially habitable worlds.”
The paper has been accepted for publication in Monthly Notices of The Royal Astronomical Society and is available for download here.
