Exoplanet Fomalhaut b On the Move

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Enlarge and enjoy.  Fomalhaut b on its very long (1,700 year) and elliptica orbit, as seen here in five images taken by the Hubble Space Telescope over seven years.  The reference to “20 au” means that the bar shows a distance of 20 astronomical units, or 20 times the distance from the sun to the Earth. (Jason Wang/Paul Kalas; UC Berkeley)

Direct imaging of exoplanets remains in its infancy, but goodness what a treat it is already and what a promise of things to come.

Almost all of the 3,714 exoplanets confirmed so far were detected via the powerful but indirect transit and radial velocity methods — measures of slightly decreased light as a planet crosses in front of its star, or the measured wobble of a star caused by the gravitational pull of a planet.

But now 44 planets have also been detected by telescopes — in space and on the ground — looking directly at distant stars.  Using increasingly sophisticated coronagraphs to block out the blinding light of the stars, these tiny and often difficult-to-identify specks are nonetheless results that are precious to scientists and the public.

To me, they make exoplanet science accessible as perhaps nothing else so far.  Additionally, they strike me as moving — and I don’t mean in orbit.  Rather, as when you see your own insides via x-rays or MRIs, direct imaging of exoplanets provides a glimpse into the otherwise hidden realities of our world.

And in the years ahead – actually, most likely the decades ahead — this kind of direct imaging of our astronomical neighborhood will become increasingly powerful and common.

This is how the astronomers studying the Fomalhaut system describe what you are seeing:

“The Fomalhaut system harbors a large ring of rocky debris that is analogous to our Kuiper belt. Inside this ring, the planet Fomalhaut b is on a trajectory that will send it far beyond the ring in a highly elliptical orbit.

“The nature of the planet remains mysterious, with the leading theory being the planet is surrounded by its own ring or a sphere of dust.”

 

A simulation of one possible orbit for Fomalhaut b derived from the analysis of Hubble Space Telescope data between 2004 and 2012, presented in January 2013 by astronomers Paul Kalas and James Graham of Berkeley, Michael Fitzgerald of UCLA and Mark Clampin of NASA/Goddard. (Paul Kalas)

Fomalhaut b was first described in 2008 by Paul Kalas, James Graham and colleagues at the University of California, Berkeley.   If not the first object identified through direct imaging — a brown dwarf failed star preceded it, as well as other objects that remain planet candidates — Fomalhaut was among the very first.  The data came via the Advanced Camera for Surveys on the Hubble Space Telescope.

But Fomalhaut b is an unusual planet by any standard, and that resulted in a lot of early debate about whether it really was a planet.  Early efforts to confirm the presence of the planet failed, in part because the efforts were made in the infrared portion of the spectrum.

Instead, Fomalhaut b had been detected only in the optical portion of the spectrum, which is uncommon for a directly imaged planet. More specifically, it reflects bluish light, which again is unusual for a planet.  Some contended that the planet detection made by Hubble was actually a noise artifact.

A pretty serious debate ensued in 2011 but by 2013 the original Hubble data had been confirmed by two teams and its identity as a planet was broadly embraced, although the noise of the earlier debate to some extent remains.

As Kalas told me, this is probably because “no one likes to cover the end of a debate.”  Nonetheless, he said, it is over.

“Fomalhaut b at age 440 Myr (.44 billion years) is much older than the other directly imaged planets,” Kalas explained. “The younger the planet, the greater the infrared light it emits. Thus it is not particularly unusual that it is hard to image planets in the Fomalhaut system using infrared techniques.”

Kalas believes that a ring system around the planet could be reflecting the light.  Another possibility, he said, is that two dwarf planets collided and a compact dust cloud surrounding a dwarf planet is moving through the Fomalhaut system.

That scenario would be very difficult to test, he said, but the alternate possibility of a Saturnian exoplanet with a ring is something that the James Webb Space Telescope will be able to explore.

In any case, the issue of whether or not the possibly first directly-imaged planet is in fact a planet has been resolved for now.

When the International Astronomical Union held a global contest to name some of the better known exoplanets several years ago, one selected for naming was Fomalhaut b, which also now has the name “Dagon.”  The star Fomalhaut is the brightest in the constellation Pisces Australis — the Southern Fish — and Dagon was a fish god of the ancient Philistines.

 

This video of Beta Pictoris and its exoplanet was made using nine images taken with the Gemini Planet Imager over more than two years years.  The planet is expected to come our from behind its star later this year, and the GPI team hopes to capture that event. (Jason Wang; UC Berkeley, Gemini Planet Imager Exoplanet Survey)

While instruments on the W.M. Keck Observatory in Hawaii, the European Very Large Telescope in Chile and the Hubble Space Telescope have succeeded in directly imaging some planets, the attention has been most focused on the two relatively newcomers.  They are the Gemini Planet Imager (GPI), now on the Gemini South Telescope in Chile and funded largely by American organizations and universities, and the largely European Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument, also in Chile.

In real time, the two instruments correct for distorting atmospheric turbulences around Earth and also block the intense light of the host stars. Any residual incoming light is then scrutinized, and the brightest spots suggest a possible planet and can be photographed as such.

The ultimate goal is have similar instruments improved until they are powerful enough to read the atmospheres of the planets through spectroscopy, which has been done so far only to a limited extent.

Kalas, Graham and Jason Wang (a graduate student at Berkeley who put together the direct imaging movies ) are part of the GPI team, which since 2014 has been searching for Jupiter-sized and above planets orbiting some distance from their suns.  The group is a member of NASA’s NExSS initiative to encourage exoplanet scientists from many disciplines to work together.

While GPI has had successes detecting important exoplanets such as 51 Eridani b, it also studies already identified planets to increase understanding of their orbits and their characteristics.

The Gemini Planet Imager when it was being connected to the Gemini South Telescope in Chile. (Gemini Observatory)

GPI has been especially active in studying the planet Beta Pictoris b, a super Jupiter discovered using data collected by the European Southern Observatory Very Large Telescope.  While the data was first collected in 2003, it took five years to tease out the planet orbiting the young star and it took several more years to confirm the discovery and begin characterizing the planet.

GPI has followed Beta Pictoris b for several years now, compiling orbital and other data used for video above.

The planet is currently behind its sun and so cannot be observed.  But James Graham told me that the planet is expected to emerge late this year or early next year.  It remains unclear, Graham said, whether GPI will be able to capture that emergence because it will soon be moved from the Gemini telescope in Chile to the Gemini North Telescope on Hawaii.  But he certainly hopes that it will be allowed to operate until the planet reappears.

The planet 51 Eridani b was the first exoplanet discovered by the GPI and remains one of its most important.   The planet is a million times fainter than its parent star and shows the strongest methane signature ever detected on an alien planet, which should yield additional clues as to how the planet formed.

The four-year GPI campaign from Chile has not discovered as many Jupiter-and-greater sized planets as earlier expected.  Graham said that may well be because there are fewer of them than astronomers predicted, or it may be because direct imaging is difficult to do.

But Graham said the campaign is actually nowhere near over.  Much of the data collected since 2014 remains to be studied and teased apart, and other Jupiters and super Jupiters likely are hidden in the data.

Right now the exoplanet science community, and especially those active in direct imaging, are anxiously awaiting a decision by NASA, and then Congress, about the fate of the Wide Field Infrared Survey Telescope (WFIRST.)

Designed to be the first space telescope to carry a coronagraph and consequently a major step forward for direct imaging, it was scheduled to be NASA’s big new observatory of the 2020s.

But the Trump Administration cancelled the mission earlier this year, Congress then restored it but with the caveat that NASA had to provide a detailed plan for its science, its technology and its cost.  That plan remains an eagerly-awaited work in progress.

Meanwhile, here is another example of what direct imaging, with the help of soon-to-be Caltech postdoc Jason Wang, can provide.  The video of the HR 8799 system went viral when first made public in early last year.

 

The four planet system orbiting the planet HR 8977, first partially identified in 2008 by Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics and Bruce Macintosh of Stanford and others.   The video was created in 2017 after all four planets had been identified via direct imagine and their orbits had been followed for some years. (Jason Wang of UC Berkeley/Christian Marois of NRC Herzberg.)

The promise of direct imaging is enormous.  The collected photons can be used for spectroscopy that can potentially tell scientists about a planet’s radius, mass, age, effective temperature, clouds, molecular composition, rotation rate and atmospheric dynamics.

For a small, potentially habitable planet, direct imaging can measure surface temperate and pressure and determine whether it can support liquid water.  It can also potentially determine if the atmosphere is in the kind of disequilibrium regarding oxygen, ozone and perhaps methane that signal the presence of life.

But almost all this is in the future since none of the current instruments are powerful enough to collect that data.

In the meantime, researchers such as Berkeley graduate student Lea Hirsch, soon to be a Stanford postdoc,  are focused on using the strengths of the different detection methods to come up with constraints on exoplanetary characteristics (such as mass and radius) that one technique alone could not provide.

University of California at Berkeley astronomy grad student Lea Hirsch at Lick Observatory. She will be going soon to Stanford University for a postdoc with Gemini Planet Imager Principal Investigator Bruce Macintosh.

For instance, the transit technique works best for identifying planets close to their stars, direct imaging is the opposite and radial velocity is best that detecting large and relatively close-in planets.  Radial velocity gives a minimum (but not maximum) mass, while transits provide an exoplanet radius.

What Hirsch would like to do is determine constraints (limits) on the size of exoplanets using both radial velocity measurements and direct imaging.

As she explained, radial velocity will give that minimum mass, but nothing more in terms of size.  But in an indirect way for now, direct imaging can provide some maximum mass.

If, for instance, astronomers know through the radial velocity method that exoplanet X orbits a certain star and is twice the size of Jupiter, they can then look for it using direct imaging with confidence that something is there.  Let’s say the precision of the imaging is such that if a planet six times the size of Jupiter was present they would — over a period of time — detect it.

A detection would indeed be great and the planet’s mass (and more) would then be known.  But if no planet is detected — as often happens — then astronomers still collect important information.  They know that the planet they are looking for is less than six Jupiter masses.  Since the radial velocity method already determined it was at least larger than two Jupiters, scientists would then know that the planet has a mass of between two and six Jupiters.

“All the techniques in our toolkit {of exoplanet searching} have their strengths and weaknesses,” she said.  “But using those techniques together is part of our future because there’s a potential to know much more.”

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A Four Planet System in Orbit, Directly Imaged and Remarkable

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Now on Facebook:  http://facebook.com/nexssmanyworlds/

The era of directly imaging exoplanets has only just begun, but the science and viewing pleasures to come are appealingly apparent.

This evocative movie of four planets more massive than Jupiter orbiting the young star HR 8799 is a composite of sorts, including images taken over seven years at the W.M. Keck observatory in Hawaii.

The movie clearly doesn’t show full orbits, which will take many more years to collect. The closest-in planet circles the star in around 40 years; the furthest takes more than 400 years.

But as described by Jason Wang,  an astronomy graduate student at the University of California, Berkeley, researchers think that the four planets may well be in resonance with each other.

In this case it’s a one-two-four-eight resonance, meaning that each planet has an orbital period in nearly precise ratio with the others in the system.

The black circle in the center of the image is part of the observing and analyzing effort to block the blinding light of the star, and thus make the planets visible.

The images were initially captured by a team of astronomers including Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics, who analyzed the data.  The movie animation was put together by Wang, who is part of the Berkeley arm of the Nexus for Exoplanet System Science (NExSS), a NASA-sponsored group formed to encourage interdisciplinary exoplanet science.

The star HR 8799 has already played a pioneering role in the evolution of direct imaging of exoplanets.  In 2008, the Marois group announced discovery of three of the four HR 8799 planets using direct imaging for the first time. On the same day that a different team announced the direct imaging of a planet orbiting the star Fomalhaut.

 


This false-color composite image traces the motion of the planet Fomalhaut b, a world captured by direct imaging. (NASA, ESA, and P. Kalas, University of California, Berkeley and SETI Institute)

HR 8799 is 129 light years away in the constellation of Pegasus.  By coincidence, it is quite close to the star 51 Pegasi, where the first exoplanet was detected in 1995.  It is less than 60 million years old, Wang said, and is almost five times brighter than the sun.

Wang said that the animation is based on eight observations of the planets since 2009.  He then used a motion interpolation algorithm to draw the orbit between those points.

Much can be learned from the motion of the planets, however long it may take for them to circle their sun.  Based on the Keck observations, astronomers have concluded that the four planets orbit in roughly Keplerian motion around the star — almost circular, but not entirely.

Jason Wang is a graduate student in astronomy at the University of California, Berkeley.

The planets are quite far from each other, which is to be expected due to their enormous size.   Because of those large separations, Wang said astronomers will be watching to see if the system is stable or if some of the planets may be ejected from the system.

Although the first three HR 8799 planets were officially discovered in 2008,  researchers learned afterwards that the planets had actually already been observed.  The “precovery” had been made in 1998 by the NICMOS instrument on the Hubble Space Telescope, but was teased out only after a newly developed image-processing technique was installed.

Christian Marois was part of the team that discovered HR 8799 using direct imaging. He is also on the engineering and science teams of the Gemini Planet Imager, which he helped design and build.

The fourth HR 8799 planet was found after further observations in 2009–2010.  That planet orbits inside the first three planets, but is still fifteen times the distance from its sun than Earth to our sun.  (The team working with Marois included Quinn Konopacky of the University of California, San Diego, Bruce Macintosh of Stanford University, Travis Barman of the University of Arizona and Ben Zuckerman of UCLA.)

James Graham is leader of the Berkeley NExSS group, and he was struck by some of the connections between what has been found around HR 8799 and what exists in our own solar system.

For instance, he said that “it’s delightful that these recently discovered planets exhibit the same type of harmony exhibited by the Galilean moons, Io, Europa, and Ganymede (1:2:4) and illustrating some of the connections between our own solar system and those orbiting other stars. ”

The outer planet orbits inside a dusty disk like our Kuiper Belt. It is one of the most massive disks known around any star within 300 light years of Earth, and there is room in the inner system for rocky planets.

Both Wang and Marois are also on the team operating the Gemini Planet Imager, a cutting-edge addition to the Gemini South telescope in Atacama Desert of Chile.

The GPI includes a next-generation adaptive optics instrument that allows for much clearer seeing through the Earth’s atmosphere by correcting for turbulence.  The result is better direct imaging.   A key goal of the GPI project is to image large extrasolar planets orbiting at distances from their host stars similar to, or greater than, between Jupiter and our sun.

This looping animation of a series of images taken between November 2013 and April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile shows the exoplanet Beta Pictoris b orbiting the star Beta Pictoris. In the images, the star is at the center of the left-hand edge of the frame; it is hidden by the Gemini Planet Imager’s coronagraph. We are looking at the planet’s orbit almost edge-on. (M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute)

The idea for the HR 8799 movie came from a similar, but less elaborate, orbital animation of a planet detected by GPI circling the star Beta Pictoris.

It was initially thought (and hoped) that the planet might transit in front of Beta Pictoris,  providing a unique opportunity to learn the radius of the planet and thus understand the size of the atmosphere.  Unfortunately, the geometry of the planet’s orbit doesn’t quite line up in a way that would have the planet pass in front of the star from our point of view.

However, although the planet doesn’t transit, what is called its Hill sphere does. The Hill sphere is the region surrounding the planet where its gravitational influence dominates over the gravitational influence of the star. As a result, the remnants of the disk left over from planet formation, planetary rings and moons could transit the star later this year and may be detectable.

Those smaller bodies are unlikely to be the subject of any evocative movie animations, but direct imaging will be bringing many more of them to us in the days ahead.

“The Beta Pic animation looked so cool that we’ve wanted to do more,” Wang said, explaining why the HR 8799 movie was made.  “We wanted to make one that was even more impactful for the audience and could begin to show what one of these systems looks like.”

I think they succeeded.

 

 

 

 

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Direct Imaging Earth and Moon from Mars

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(NASA/ JPL-Caltech/ Univ. of Arizona)

Sometimes images arrive that make it clear that the space age is not a throw-away line, but a reality.

This one was taken by a satellite orbiting Mars, and it shows the Earth and the moon.  Kind of remarkable, given that the camera — the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter — was 127 million miles away

And HiRISE is not a far-seeing telescope, but rather a camera designed to look down on Mars from 160 to 200 miles away.  It’s job (among other tasks) is to image the terrain, measure the compounds and minerals below, and keep an eye on Mars dust storms, climate, and the downhill steaks that periodically appear on some inclines and may contain surface salty water.

The image is a composite image of Earth and its moon, combining the best Earth image with the best moon image from four sets of images acquired on Nov. 20, 2016 by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter.

Each was separately processed prior to combining them so that the moon is bright enough to see. The moon is much darker than Earth and would barely be visible at the same brightness scale as Earth. The combined view retains the correct sizes and positions of the two relative to each other.

This is how JPL described the details:

HiRISE takes images in three wavelength bands: infrared, red, and blue-green. These are displayed here as red, green, and blue, respectively. This is similar to Landsat images in which vegetation appears red. The reddish feature in the middle of the Earth image is Australia. Southeast Asia appears as the reddish area (due to vegetation) near the top; Antarctica is the bright blob at bottom-left. Other bright areas are clouds.

What I find especially intriguing about the image is that it is precisely the kind of “direct imaging” that the exoplanet community hopes to some day do with distant planets.  With this kind of imaging, scientists not only can detect the glints of water, the presence of land, the dynamics of clouds and climate, but they can also get better spectrographic measurements of what chemicals are present.

Some exoplanets are being painstakingly direct imaged, but the difficulty factor is high and the result is most likely one or two pixels.  And since the planets are orbiting stars that send out light that hides any exoplanets present, coronagraphs are needed inside the telescopes to block out the sun and its rays.

Enormous, unfolding “starshades” sent to space may some day perform the same function in tandem with a space telescope. Advocates for the technology say it will provide greater opportunity and sensitivity.

More on this in the weeks ahead.

Here is another Earth/moon image taken by HiRISE in 2007, when our distance Mars was 88 million miles.  Here the Earth diameter is about 90 pixels and the moon diameter is 24 pixels.

 

(NASA/JPL-Caltech/University of Arizona)

 

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Movement in The Search For ExoLife

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A notional version of an observatory for the 2030s that could provide revolutionary direct imaging of exoplanets. GSFC/JPL/STScI
A notional version of an observatory for the 2030s that could provide revolutionary direct imaging of exoplanets. GSFC/JPL/STScI

Assuming for a moment that life exists on some exoplanets, how might researchers detect it?

This is hardly a new question.  More than ten years ago, competing teams of exo-scientists and engineers came up with proposals for a NASA flagship space observatory capable of identifying possible biosignatures on distant planets. No consensus was reached, however, and no mission was developed.

But early this year, NASA Astrophysics Division Director Paul Hertz announced the formation of four formal Science and Technology Definition Teams to analyze proposals for a grand space observatory for the 2030s.  Two of them in particular would make possible the kind of super-high resolution viewing needed to understand the essential characteristics of exoplanets.  As now conceived, that would include a capability to detect molecules in distant atmospheres that are associated with living things.

These two exo-friendly missions are the Large Ultraviolet/Optical/Infrared (LUVOIR) Surveyor and the Habitable Exoplanet (HabEx) Imaging Mission.   Both would be on the scale of, and in the tradition of, scientifically and technically ground-breaking space observatories such as the Hubble and the James Webb Space Telescope, scheduled to launch in 2018.  These flagship missions provide once in a decade opportunities to move space science dramatically forward, and not-surprisingly at a generally steep cost.

 

A simulated spiral galaxy as viewed by Hubble, and the proposed High Definition Space Telescope (HDST) at a lookback time of approximately 10 billion years (z = 2) The renderings show a one-hour observation for each space observatory. Hubble detects the bulge and disk, but only the high image quality of HDST resolves the galaxy’s star-forming regions and its dwarf satellite. The zoom shows the inner disk region, where only HDST can resolve the star-forming regions and separate them from the redder, more distributed old stellar population. Image credit: D. Ceverino, C. Moody, G. Snyder, and Z. Levay (STScI)500 light years away, as imaged by Hubble and potential of the kind of telescope the exoplanet community is working towards.
A simulated spiral galaxy as viewed by Hubble, and as viewed by the kind of high definition space telescope now under study.   Hubble detects the bulge and disk, but only the high definition image resolves the galaxy’s star-forming regions and its dwarf satellite. The zoom shows the inner disk region, where only high definition can resolve the star-forming regions and separate them from the redder, more distributed old stellar population. (D. Ceverino, C. Moody, G. Snyder, and Z. Levay (STScI)

 

Because the stakes are so high, planning and development takes place over decades — twenty years is the typical time elapsed between the conception of a grand flagship mission and its launch.  So while what is happening now with the science and technology definition teams  is only a beginning — albeit one with quite a heritage already — it’s an essential, significant and broadly-supported start.  Over the next three years, the teams will undertake deep dives into the possibilities and pitfalls of LUVOIR and HabEx, as well as the two other proposals.  There’s a decent chance that a version of one of the four will become a reality.

Aki Roberge, an astrophysicist at the Goddard Space Flight Center and staff scientist of the LUVOIR study, said that the explicit charge to the teams is to cooperate rather than compete.  Any of the four observatories under consideration, she said, would enable transformative science. But from an exoplanet perspective, the possibilities she described are pretty remarkable.

“What we’re aiming for is the capability to really search for the true Earth analogues out there, the Earth-sized planets in the habitable zones of sun-like stars.  We need to understand their atmospheres, their climates, their compositions.  And ultimately, the goal is to search for life.”

The co-chair of the HabEx team, Bertrand Menneson of the Jet Propulsion Lab, said the goals are the same:  A major jump forward in our ability to understand exoplanets and a serious effort to find life.

 

actual image of venus crossing in front of the sun. Exoplanets will not be imaged like this in our lifetimes, but this is the goal.
Actual image of Venus crossing in front of the sun in 2012 taken by NASA’s Solar Dynamics Observatory. Exoplanets will not be imaged like this in our lifetimes, but this is the ultimate goal.

 

The field of exoplanet detection and research has exploded over the past two decades, with an essential boost from increasingly capable observatories on Earth and in space.  With at least three more major exoplanet-friendly space telescopes scheduled (or planned) for the next decade — as well as first light at several enormous ground-based mirrors — the brisk pace of discoveries is sure to continue.

So why are so many scientists in the field convinced that a grand, Flagship-class NASA space observatory is essential, and that it needs to be developed and built ground-up with exoplanet research in mind?  Can’t the instruments in use today, and planned for the next decade, provide the kind of observing power needed to continue making breakthroughs?

Well, no, they can’t and won’t.  That has been the conclusion of numerous studies over the years, and most recently an in-depth effort by the Association of Universities for Research in Astronomy (AURA,)   http://www.hdstvision.org/report which last summer called for development of a 12-meter (about 44 feet across) High Definition Space Telescope with the super high resolution needed to study exoplanets.  Generally speaking, a larger light-collecting mirror allows astronomers and astrophysicists to see further and better.

 

A direct, to-scale, comparison between the primary mirrors of the Hubble Space Telescope, James Webb Space Telescope, and the proposed High Definition Space Telescope (HDST). In this concept, the HDST primary is composed of 36 1.7 meter segments. Smaller segments could also be used. An 11 meter class aperture could be made from 54 1.3 meters segments. Image credit: C. Godfrey (STScI)
A direct, to-scale, comparison between the primary mirrors of the Hubble Space Telescope, James Webb Space Telescope, and the High Definition Space Telescope (HDST) proposed by the AURA group. In this concept, the HDST primary is composed of 36 1.7 meter segments.  The LUVOIR mirror under consideration is in the eight to twelve meters range. C. Godfrey (STScI)

 

The group, headed by Julianne Dalcanton of the University of Washington and Sara Seager of MIT, began with this overview of the state of play when it comes to exoplanets, instruments, and what is possible now and might be in the future:

While we now have a small sample of potentially habitable planets around other stars, our current telescopes lack the power to confirm that these alien worlds are truly able to nurture life. This small crop of worlds may have temperate, hospitable surface conditions, like Earth.

But they could instead be so aridly cold that all water is frozen, like on Mars, or so hot that all potential life would be suffocated under a massive blanket of clouds, like on Venus. Our current instruments cannot tell the difference for the few rocky planets known today, nor in general, for the larger samples to be collected in the future.

Without better tools, we simply cannot see their atmospheres and surfaces, so our knowledge is limited to only the most basic information about the planet’s mass and/ or size, and an estimate of the energy reaching the top of the planet’s atmosphere. But if we could directly observe exoplanet atmospheres, we could search for habitability indicators (such as water vapor from oceans) or for signs of an atmosphere that has been altered by the presence of life (by searching for oxygen, methane, and/or ozone).

A central goal for both LUVOIR and HabEx is to provide that “seeing” through much more sophisticated direct imaging — that is, capturing the actual reflected light from exoplanets rather than relying on indirect techniques and measurements.  The many indirect methods of finding and studying exoplanets have played and will continue to play an essential role.  But there is now a community consensus that next generation direct imaging from space is the gold standard.

 

Kepler exoplanets candidates, both confirmed and unconfirmed, orbiting G, K, and M type main sequence stars, by radii and fraction of the total. (Natalie Batalha and Wendy Stenzel, NASA Ames)
There are more than 4,000 Kepler exoplanets candidates, both confirmed and unconfirmed, orbiting G, K, and M type main sequence stars.  This graphic shows their distribution by radii and fraction of the total. (Natalie Batalha and Wendy Stenzel, NASA Ames)

That a major space observatory for the 2030s just might be exoplanet-focused reflects a definite maturing of the field.  From a science perspective, the discoveries of the Kepler mission in particular made clear that exoplanets are everywhere, and not infrequently orbiting in habitable zones.  The work of the Curiosity rover on Mars, and especially the conclusion that the planet once was wet and “habitable,” added to the general interest and excitement about possible life beyond Earth.

And then there are the lessons learned from the earlier bruising battles among exoplanet scientists, who had developed a reputation for serious in-fighting.  THEIA, the Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy, was put forward as a flagship direct imaging mission in 2010, when the Astronomy and Astrophysics Decadal Survey that sets priorities for the field was being put together by the National Academy of Sciences.  But THEIA was not adopted.

A cartoon from Chas Beichman’s ExoPAG presentation illustrates the infighting within the exoplanet science community during the 2010 decadal survey, with cosmologists, represented by “dark energy” to the side, ready to reap the benefits of that debate.
A cartoon from a exoplanet science presentation illustrates the infighting within the exoplanet science community during the 2010 decadal survey, with cosmologists, represented by “dark energy” to the side, ready to reap the benefits of that debate. ( Chas Beichman)

With the 2020 Decadal Survey on the horizon, exoplanet scientists have tried to limit conflicts and to work with the larger astronomy community.  The formal NASA/community study group, the Exoplanet Exploration Program Analysis Group (ExoPAG), brought two related groups together and ultimately recommended the intensified study for LUVOIR, HabEx and the two other proposals —  which focus on black holes, ancient galaxy formation, and other aspects of the early cosmos.  https://exep.jpl.nasa.gov/files/exep/ExoPAG_Large_Missions.pdf

When completed, the studies will go to the National Academy of Sciences for further review, discussion, and ultimately a recommendation to NASA regarding which project should go forward.

The leader of the ExoPAG  group was astronomer Scott Gaudi of Ohio State University, who specializes in characterizing exoplanets but played no favorites in the ExoPAG report and recommendations.

“What we want is to set up a fair process of intense review so the most compelling science can be chosen to go forward.  At this point, we don’t know if the necessary technologies will be available in time, and we don’t know what the costs will be.  There’s only so much money that comes from NASA for our (astrophysics) community, and maybe a top choice will cost more than the community is willing to spend.  So there are so many factors to consider.”

(The LUVOIR mission is generally considered to be somewhat more ambitious than HabEx, and would require a larger telescope mirror — greater than 8 meters across –and more funding.  Flagship missions are expensive, as NASA learned once again with the James Webb telescope, which will have cost $8.8 billion by the time of its scheduled launch.)

I asked Gaudi if the seemingly substantial public interest in exoplanets could play any role in subsequent decision-making, and he replied that it possibly would.  “In the past five or ten years, exoplanets have become a prominent topic for sure.  And the public is clearly very, very interested in that topic.”  But that public interest, he said, won’t mean much if the science and technical feasibility isn’t there.

Scott Gaudi, chairman of ExoPAG in 2015.
Scott Gaudi, chairman of ExoPAG in 2015.

We won’t know for some years if the stars will align in a way that will lead to a major observatory with direct imaging and exoplanets at its center.  But for those active in the field, the opportunity to take part in a major effort to formally determine its scientific merit and feasibility is irresistible.

Shawn Domagal-Goldman, a research space scientist at Goddard, was selected to be a deputy on the LUVOIR science and technology team, which he sees as a much-anticipated “proof of concept” effort for the exoplanet research of the future.

Between 12 and 18 scientists and engineers will be selected by NASA headquarters for each team, and Domagal-Goldman said it’s essential that they make up a broad and inter-disciplinary group, including people from industry.  Scientists from abroad not associated with an American institution can’t be formal members, but they can observe and may become more involved if their national space agencies decide to join in the effort. He encourages researchers — from newly minted PhDs to career scientists — to nominate themselves to join.

“Nobody gets paid for this, it’s a labor of love,” he said.  “But what would be more satisfying than having some of your intellectual contribution go into the formulation of missions like these.

“Direct imaging of exoplanets is clearly a direction where the community is headed. These are the missions of the future in one form or another, and if you’re a PhD or postdoc who’s qualified, this could be your career.”

Of course, it just might make the greatest discovery of modern science — finding life beyond Earth.

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