15,000 Galaxies in One Image

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Astronomers have just assembled one of the most comprehensive portraits yet of the universe’s evolutionary history, based on a broad spectrum of observations by the Hubble Space Telescope and other space and ground-based telescopes.  Each of the approximately 15,000 specks and spirals are galaxies, widely distributed in time and space. (NASA, ESA, P. Oesch of the University of Geneva, and M. Montes of the University of New South Wales)

Here’s an image to fire your imagination: Fifteen thousand galaxies in one picture — sources of light detectable today that were generated as much as 11 billion years ago.

Of those 15,000 galaxies, some 12,000 are inferred to be in the process of forming stars.  That’s hardly surprising because the period around 11 billions years ago has been determined to be the prime star-forming period in the history of the universe.  That means for the oldest galaxies in the image, we’re seeing light that left its galaxy but three billion years after the Big Bang.

This photo mosaic, put together from images taken by the Hubble Space Telescope and other space and ground-based telescopes, does not capture the earliest galaxies detected. That designation belongs to a galaxy found in 2016 that was 420 million years old at the time it sent out the photons just collected. (Photo below.)

Nor is it quite as visually dramatic as the iconic Ultra Deep Field image produced by NASA in 2014. (Photo below as well.)

But this image is one of the most comprehensive yet of the history of the evolution of the universe, presenting galaxy light coming to us over a timeline up to those 11 billion years.  The image was released last week by NASA and supports an earlier paper in The Astrophysical Journal by Pascal Oesch of Geneva University and a large team of others.

And it shows, yet again, the incomprehensible vastness of the forest in which we are a tiny leaf.

Some people apparently find our physical insignificance in the universe to be unsettling.  I find it mind-opening and thrilling — that we now have the capability to not only speculate about our place in this enormity, but to begin to understand it as well.

The Ultra-Deep field composite, which contains approximately 10,000 galaxies.  The images were collected over a nine-year period.  {NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)} 

For those unsettled by the first image, here is the 2014 Ultra Deep Field image, which is 1/14 times the area of the newest image.  More of the shapes in this photo look to our eyes like they could be galaxies, but those in the first image are essentially the same.

In both images, astronomers used the ultraviolet capabilities of the Hubble, which is now in its 28th year of operation.

Because Earth’s atmosphere filters out much ultraviolet light, the space-based Hubble has a huge advantage because it can avoid that diminishing of ultraviolet light and provide the most sensitive ultraviolet observations possible.

That capability, combined with infrared and visible-light data from Hubble and other space and ground-based telescopes, allows astronomers to assemble these ultra deep space images and to gain a better understanding of how nearby galaxies grew from small clumps of hot, young stars long ago.

The light from distant star-forming regions in remote galaxies started out as ultraviolet. However, the expansion of the universe has shifted the light into infrared wavelengths.

These images, then,  straddle the gap between the very distant galaxies, which can only be viewed in infrared light, and closer galaxies which can be seen across a broad spectrum of wavelengths.

The farthest away galaxy discovered so far is called GN-z11 and is seen now as it was 13.4 billion years in the past.  That’s  just 400 million years after the Big Bang.

GN-z11 is surprisingly bright infant galaxy located in the direction of the constellation of Ursa Major. Thus NASA video explains much more:

The farthest away galaxy ever detected — GN-z11. {NASA, ESA, P. Oesch (Yale University, Geneva University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)} 

 

Galaxy formation chronology, showing GN-z11 in context. Hubble spectroscopically confirmed the farthest away galaxy to date. {NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)}

In addition representing cutting-edge science — and enabling much more — these looks into the most distant cosmic past offer a taste of what the James Webb Space Telescope, now scheduled to launch in 2021, is designed to explore.  It will have greatly enhanced capabilities to explore in the infrared, which will advance ultra-deep space observing.

But putting aside the cosmic mysteries that ultra deep space and time astronomy can potentially solve, the images available today from Hubble and other telescopes are already more than enough to fire the imagination about what is out there and what might have been out there some millions or billions of years ago.

A consensus of exoplanet scientists holds that each star in the Milky Way galaxy is likely to have at least one planet circling it, and our galaxy alone has billions and billions of stars.  That makes for a lot of planets that just might orbit at the right distance from its host star to support life and potentially have atmospheric, surface and subsurface conditions that would be supportive as well.

A look these deep space images raises the question of how many of them also house stars with orbiting planets, and the answer is probably many of them.  All the exoplanets identified so far are in the Milky Way, except for one set of four so far.

Their discovery was reported earlier this year by Xinyu Dai, an astronomer at the University of Oklahoma, and his co-author, Eduardo Guerras.  They came across what they report are planets while using NASA’s Chandra X-ray Observatory to study the environment around a supermassive black hole in the center of a galaxy located 3.8 billion light-years away from Earth.

In The Astrophysical Journal Letters , the authors report the galaxy is home to a quasar, an extremely bright source of light thought to be created when a very large black hole accelerates material around it. But the researchers said the results of their study indicated the presence of planets in a galaxy that lies between Earth and the quasar.

Furthermore, the scientists said results suggest that in most galaxies there are hundreds of free-floating planets for every star, in addition to those which might orbit a star.

The takeaway for me, as someone who has long reported on astrobiology and exoplanets, is that it is highly improbable that there are no other planets out there where life occurs, or once occurred.

As these images make clear, the number of planets that exist or have existed in the universe is essentially infinite.  That no others harbor life seems near impossible.

 

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Of White Dwarfs, “Zombie” Stars and Supernovae Explosions

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Artistic view of the aftermath of a supernova explosion, with an unexpected white dwarf remnant. These super-dense but no longer active stars are thought to play a key role in many supernovae explosion. (Copyright Russell Kightley)
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White dwarf stars, the remnant cores of low-mass stars that have exhausted all their nuclear fuel, are among the most dense objects in the sky.
 
Their mass is comparable to that of the sun, while their volume is comparable to that of Earth. Very roughly, this means the average density of matter in a white dwarf would be on the order of 1,000,000 times greater than the average density of the sun.
 
Thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star — a category that includes the sun and over 97% of the other stars in the Milky Way — they are dim objects first identified a century ago but only in the last decade the subject of broad study.
 
In recent years the white dwarfs have become more and more closely associated with supernovae explosions, though the processes involved remained hotly debated.  A team using the Hubble Space Telescope even captured  before and after images of what is hypothesized to be an incomplete white dwarf supernova.  What was left behind has been described by some as a “zombie star.”
 
Now a team of astronomers led by Stephane Vennes of the Czech Academy of Sciences has detected another zombie white dwarf, LP-40-365 , that they put forward as a far-flung remnant of a long-ago supernova explosion.  This is considered important and unusual because it would represent a first detection of such a remnant long after the supernova conflagration.
 
This dynamic is well captured in an animation accompanying the Science paper that describes the possible remnant.  Here’s the animation and a second-by-second description of what is theorized to have occurred:
 
 
00.0 sec: Initial binary star outside the disk of the Milky Way galaxy. A massive white dwarf accreting
material through an accretion disk from its red giant companion star. The stars orbit around the center of
mass of the binary system.
 
14.6 sec: The white dwarf reaches the Chandrasekhar mass limit and explodes as a bright Type Ia
supernova. However, the explosion is not perfect; a fraction of the white dwarf shoots out like a shrapnel to the left. The binary system disrupts.
 
18.0 sec: The supernova explosion again, at an edge – on view. The shrapnel comes at the viewer and passes by.
 
20.0 sec: After passing by, the remnant flies off towards the disk of the Milky Way towards the spiral arm with the Solar System.
 
24.0 sec : The fast moving remnant from the solar neighborhood as it passes by the stars in our galactic arm, including the Sun. The remnant gets in the reach of our telescopes. (Copyright Sardonicus Pax)

 

A supernova — among the most powerful forces in the universe — occurs when there is a change in the core of a star. A change can occur in two different ways, with both resulting in a thermonuclear explosion.

Type Ia supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.

The second type takes place only in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova.

Type Ia supernovae, which are the result of the complete destruction of the star in a thermonuclear explosion, have a fairly uniform brightness that makes them useful for cosmology. The light emitted by the supernova explosion can be, for a short while at least, as bright as the whole of the Milky Way.

Recently, astronomers have discovered a related form of supernova, called Type Iax, which look like Type Ia, but are much fainter. Type Iax supernovae may be caused by the partial destruction of a white dwarf star in such an explosion. If that interpretation is correct, part of the white dwarf should survive as a leftover object.

And that leftover object is precisely what Vennes et al claim to have found.

They have identified LP 40-365 as an unusual white dwarf with a low mass, high velocity and strange composition of oxygen, sodium and magnesium  – exactly as might be expected for the leftover star from a Type Iax event. Vennes describes the white dwarf remnant his team has detected as a “compact star,” and perhaps the first of its kind in terms of the elements it contains.

The team calculate that the explosion must have occurred between five and 50 million years ago.

 

The two inset images show before-and-after images captured by NASA’s Hubble Space Telescope of Supernova 2012Z in the spiral galaxy NGC 1309, what some call a “zombie star.”. The white X at the top of the main image marks the location of the supernova in the galaxy. A supernova typically obliterates the exploding white dwarf, or dying star.  In 2014, scientists found that this faint supernova may have left behind a surviving portion of the white dwarf star.(NASA,ESA)

 

In an email exchange, Vennes told me that he has been studying the local white dwarf population for thirty years.

“These compact, dead stars tell us a lot about the “old” Milky Way, how stars were born and how they died,” he wrote.

“Tens of thousands of these white dwarfs have been catalogued over this past century, most of them in the last decade, but we keep an eye on outliers, objects that are out of the norm. We look for exceedingly large velocity, peculiar chemical composition or abnormal mass or radii.

Stephane Vennes, a longtime specialist in white dwarf stars at the Czech Academy of Science.

“The strange case of LP40-365 came unexpectedly, but this was a classic case of serendipity in astronomy. Out of hundreds of targets we observed at the telescope, this one was uniquely peculiar. Fortunately, theorists are very imaginative and the model we adopted to interpret the observed properties of this object were only recently published. Our research on this object was certainly inspired and directed by their theory.”

Vennes says the team was surprised to learn that the white dwarf LP40-365 is relatively bright among its peers and that similar objects did not show up in large-scale surveys such as the Sloan Digital Sky Survey.

“This fact has convinced us that many more similarly peculiar white dwarfs await discovery. We should search among fainter, more distant samples of white dwarfs,” he wrote.

And that search can be done by the European Space Agency’s Gaia astrometric space telescope, with follow-up observations at large telescopes such as the European Southern Observatory’s Very Large Telescope and the Gemini observatory in Chile.

“It is also likely that our adopted model involving a subluminous {faint} Type Ia supernova will be modified or even superseded by teams of theorists coming up with new ideas. But we remain confident that these new ideas would still involve a cataclysmic event on the scale of a supernova.”

Here is another animated version of the cataclysm described in the paper: 

An ultra-massive and compact dead star, or white dwarf, (shown as a small white star) is accreeting matter from its giant companion (the larger red star). The material escapes from the giant and forms an accretion disk around the white dwarf.
Once enough material is accreted onto the white dwarf, a violent thermonuclear runaway tears it apart and destroys the entire system. The giant star and the surviving fragment of the white dwarf are flung into space at tremendous speeds. The surviving white dwarf shrapnel hurtles towards our region of the galaxy, where its radiation is detected by ground based telescopes. (Copyright Russell Kightley)

 

A supernova burns for only a short period of time, but it can tell scientists a lot about the universe.

One kind of supernova has shown scientists that we live in an expanding universe, one that is growing at an ever increasing rate.

Scientists also have determined that supernovas play a key role in distributing elements throughout the universe. When the star explodes, it shoots elements and debris into space. Many of the elements we find here on Earth are made in the core of stars.

These elements travel on to form new stars, planets and everything else in the universe — making white dwarfs and supernovae essential to the process that ultimately led to life.

 

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Some Spectacular Images (And Science) From The Year Past

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A rose made of galaxies

This is a golden era for space and planetary science, a time when discoveries, new understandings, and newly-found mysteries are flooding in.  There are so many reasons to find the drama intriguing:  a desire to understand the physical forces at play, to learn how those forces led to the formation of Earth and ultimately us, to explore whether parallel scenarios unfolded on planets far away, and to see how our burgeoning knowledge might set the stage for exploration.

But always there is also the beauty; the gaudy, the stimulating, the overpowering spectacle of it all.

Here is a small sample of what came in during 2016:

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The Small Magellanic Cloud, a dwarf galaxy that is a satellite of our Milky Way galaxy, can be seen only in the southern hemisphere.  Here, the Hubble Space Telescope captured two nebulas in the cloud. Intense radiation from the brilliant central stars is heating hydrogen in each of the nebulas, causing them to glow red.

Together, the nebulas are called NGC 248 and are 60 light-years long and 20 light-years wide. It is among a number of glowing hydrogen nebulas in the dwarf satellite galaxy, which is found approximately 200,000 light-years away.

The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). Astronomers are using Hubble to probe the Milky Way satellite to understand how dust is different in galaxies that have a far lower supply of heavy elements needed to create that dust.  {NASA.ESA, STSci/K. Sandstrom (University of California, San Diego), and the SMIDGE team}

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.

Probably the biggest exoplanet news of the year, and one of the major science stories, involved the discovery of an exoplanet orbiting Proxima Centauri, the star closest to our own.

This picture combines a view of the southern skies over the European Space Observatory’s 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left).

The planet Proxima Centauri b is thought to lie within the habitable zone of its star.  Learning more about the planet, the parent star and the two other stars in the Centauri system has become a focus of the exoplanet community.

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We all know about auroras that light up our far northern skies, but there’s no reason why they wouldn’t exist on other planets shielded by a magnetic field — such as Jupiter.  Astronomers using the Hubble Space Telescope have found them on the poles of our solar system’s  largest planet, and produced far ultraviolet light images taken as the Juno spacecraft approached the planet.

Auroras are formed when charged particles in the space surrounding the planet are accelerated to high energies along the planet’s magnetic field. When the particles hit the atmosphere near the magnetic poles, they cause it to glow like gases in a fluorescent light fixture. Jupiter’s magnetosphere is 20,000 times stronger than that of Earth.

The full-color disk of Jupiter in this image was separately photographed at a different time by Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of the outer planets.

Inside the Crab Nebula

Peering deep into the core of the Crab Nebula, this close-up image reveals the heart of one of the most historic and intensively studied remnants of a supernova, an exploding star. The inner region sends out clock-like pulses of radiation and tsunamis of charged particles embedded in magnetic fields.

The neutron star at the very center of the Crab Nebula has about the same mass as the sun but compressed into an incredibly dense sphere that is only a few miles across. Spinning 30 times a second, the neutron star shoots out detectable beams of energy that make it look like it’s pulsating.

The NASA Hubble Space Telescope image is centered on the region around the neutron star (the rightmost of the two bright stars near the center of this image) and the expanding debris surrounding it. Intricate details of glowing gas are shown in red and the blue glow is radiation given off by electrons spiraling at nearly the speed of light in the powerful magnetic field around the crushed stellar core.

Observations of the Crab supernova were recorded by Chinese astronomers in 1054 A.D. The nebula, bright enough to be visible in amateur telescopes, is located 6,500 light-years away in the constellation Taurus.  (NASA, ESA)

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The Gemini Planet Imager provides some of the earliest high-resolution, high-contrast direct imaging of exoplanets.  Using a coronagraph inside the telescope to block out the light of the star, the GPI can then allow researchers to see the region surrounding that star — in other words, where exoplanets might be.

This image includes a wide-angle view of the star HD 106906 taken by the Hubble Space Telescope and a close-up view from the Planet Imager, which operates on the Gemini South telescope in Chile’s Atacama Desert.  The image reveals a disturbed system of comets near the star, which may be responsible for the orbit of the the unusually distant giant planet (upper right).

The GPI Exoplanet Survey is operated by a team of astronomers from the University of California at  Berkeley and 23 other institutions, and is targeting 600 young stars to understand how planetary systems evolve over time.

Paul Kalas of UC Berkeley is responsible for the image and led the team that wrote about it. That paper actually came out in the Astrophysical Journal in late 2015 but, hey, that’s almost 2016.

Astronomers have regularly found a galaxy or star that is the furthest from us ever to be detected.  But the record is there to be broken, and in 2016 it was astronomers from the Great Observatories Origins Deep Survey (GOODS) who made the discovery.

Galaxy GN-z11, shown in the inset, was imaged as it was 13.4 billion years in the past, just 400 million years after the big bang.  That means the universe was only three percent of its current age when the light left that galaxy.

The galaxy has many blue stars that are bright and young, but it looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe.

(NASA, ESA, P. Oesch (Yale University), G. Brammer ( STScI)), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)

Biggest announce of discovred exoplanets by Kepler. (No, those are not real images, but still...)

No, these are not images of actual exoplanets, but they represent the continuing work of one of NASA’s most pioneering and productive missions, the Kepler Space Telescope. In May the Kepler team announced the detection of 1284 more planets or planet candidates as part of its newest catalog, the largest number announced at once in the mission.

To date, Kepler has identified unconfirmed 4,696 planet candidates, 2,331 confirmed planets, and 21 confirmed small planets in a habitable zone. In addition, the follow-on K2 mission has identified 458 candidate planets and 173 confirmed.

The Kepler spacecraft stared fixedly at a small portion of the sky for four years, looking to identify miniscule dimmings in the brightness of stars that would indicate that a planet was passing between the telescope and the star. In this way, Kepler has established a census of exoplanets that has been extrapolated to show the presence of billions and billions of planets around other stars.

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The 21-foot array that will collect photons for the James Webb Space Telescope was finished and put on display in November at the Goddard Space Flight Center. It will be the largest mirror to go into space, and will likely make the JWST into the most powerful and far-seeing observatory ever.

It will observe in the infrared portion of the spectrum because its goals include peering deep into the past of the universe, which is now most visible in the infrared. This means the JWST will have to be cooled to -364 degrees F, just 50 degrees above absolute zero.  To achieve that temperature, it’s insulated from the sun by five membrane layers, each no thicker than a human hair. Placing those membranes was finished in November, marking an end to construction of the telescope “mirror.”

The project has been enormously ambitious, and with that has come long delays and budget overruns that almost resulted in it being scrapped. Just this month, some early vibrating tests – designed to simulate launch conditions – experienced an anomaly that NASA engineers are working on now.  The JWST is scheduled to launch in late 2018.

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This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position of Jupiter’s moon Europa. The plumes, photographed by NASA’s Hubble’s Space Telescope Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter.

While the plumes spitting out of Saturn’s moon Enceladus are much better known now — the Cassini spacecraft flew through them in 2015, after all — the growing scientific consensus that Europa also has some plumes may be of even greater importance.  That moon is much larger, its ice-covered oceans have been determined to hold more water than all the oceans of Earth, and those oceans have clearly been around for a long time.

Hubble’s ultraviolet sensitivity allowed for the detection of the plumes, which rise more than 100 miles above Europa’s icy surface. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. (NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.)

compounds being created in the xxx nebula

How the fundamentals needed for life are created in space has been a longstanding mystery.  The cosmos, after all, began with hydrogen and helium, and that was about it.  But life needs carbon atoms connected to hydrogen, oxygen, nitrogen and other elements

Astronomers and astrochemists have been making progress in recent years and now understand the basics of how the heavier elements are formed in space.  New data from the European Space Agency’s Herschel Space Observatory has gone further and has established that ultraviolet light from stars plays a key role in creating these molecules.  Previously, scientists thought that turbulence created by “shock” events was the driving force.

This image is of the Orion nebula, where scientists studied carbon chemistry of a major star-forming region. Herschel probed an area of the electromagnetic spectrum — the far infrared, associated with cold objects — that no other space telescope has reached before so it could take into account the entire Orion Nebula instead of individual stars.

The result was a better understanding of how carbon and hydrogen reach the states necessary to bond and form the basic carbon chemistry of the cosmos (and of life.)

Within the inset image, the emission from ionized carbon atoms (C+), overlaid in yellow, was isolated and mapped out from spectrographic data.

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Following a successful close flyby of Enceladus, the NASA-ESA Cassini spacecraft captured this image of the moon with Saturn’s rings beyond.

The image was taken in visible light with the Cassini spacecraft wide-angle camera when it was about 106,000 miles away from Enceladus. That flyby turned into a fly-through as well, when Cassini entered the plumes of water vapor and dust that shoot out of the bottom of the moon.

Scientists already know that an array of organic and other chemicals are in the plumes, but the field is awaiting word about the presence (or absence) of molecular hydrogen, which is formed when water comes into contact with rocks in hydrothermal vents.  Many think that Enceledus is habitable and should be tested for signs of life because biosignatures could potentially exist in the relatively easy-to-access geysers.

moon-halo-5-13-2016-yuri-beletsky-chile-pano

While Yuri Beletsky is a staff astronomer at the Las Campanas Observatory in Chile, he is also a noted astrophotographer who specializes in capturing the beauty of nighttime scenes — usually connecting the celestial with the terrestrial.

In this 2016 photo, the moon is surrounded by a halo caused by the presence of millions of ice crystals in the upper atmosphere.  Great conditions for an astrophotographer, but pretty much useless for an astronomer.

The star within the halo is Regulus, brightest object in the constellation Leo the Lion. On the left outside the halo is Procyon from Canis Minor and on the right is the planet Jupiter.

As is so often the case in this line of endeavor, it’s quite a sight to see.

 

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More Evidence of Water Plumes On Europa Increases Confidence That They’re For Real

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 Figure 2: This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The Hubble data were taken on January 26, 2014. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. Credits: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center Image comparison of 2014 transit and 2012 Europa aurora observations

This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The Hubble data were taken on January 2014, and appear to show plumes that spit out as much as 125 miles.  The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. (NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center)

Europa is a moon no bigger than our own and is covered by deep layers of ice, but it brings with it a world of promise.  Science fiction master and sometimes space visionary Arthur C. Clarke, after all,  named it as the most likely spot in our solar system to harbor life, and wrote a “2001: A Space Odyssey”  follow-up based in part on that premise.

Many in the planetary science and astrobiology communities are similarly inclined and have supported a specifically Europa mission geared to learning more about what is generally considered to be a large ocean beneath that ice.

Along the way, Europa became the only object deemed by Congress to be an obligatory NASA destination, and formal plans for such a voyage have been under way — however slowly — for several years.  Formal development of the “Europa Clipper” flyby project began last year, after a half decade of conceptual work.

The logic for the flyby got a major boost on Monday when a team using the Hubble Space Telescope reported that they had most likely detected plumes of water erupting out of Europa on three separate occasions.

Because of the difficulty of the observation — and the fact that plumes were found on 3 out of 10 passes — nobody was willing to claim that the finding was definitive.  But coupled with an earlier identification of a Europa plume by a different team using a different technique, the probability that the plumes are real is getting pretty high.

And if there really are plumes of water vapor or ice crystals being pushed through Europa’s thick surface of ice, then the implications for the search for signs of habitability and of life on Europa are enormous.

“Europa is surely one of the most compelling astrobiological targets in solar system with its apparent saline oceans,” said William Sparks, an astronomer with Space Telescope Science Institute in Baltimore and lead author of the Europa paper, to be published in The Astrophysical Journal.

“And now there’s the real possibility that we can explore for organics or even signs of life without drilling into the ice.”  In other words, the plumes could allow NASA to collect material once in the oceans of Europa via a flyby, rather than requiring a landing and a subsequent piercing through miles of ice.

Bizarre features on Europa’s icy surface suggest a warm interior. This view of the surface and shows a color image set within a larger mosaic of low-resolution monochrome images. The Galileo spacecraft was able to survey only a small fraction of Europa's surface in color at high resolution; a future mission would include a high-resolution imaging capability to capture a much larger part of the moon's surface. (NASA/JPL-Caltech)
Beautiful and mysterious features on Europa’s icy surface suggest a warm interior and hint at the geology that could allow water to break through a weak point and erupt as a plume. This view of the surface and shows a color image set within a larger mosaic of low-resolution monochrome images. The Galileo spacecraft was able to survey only a small fraction of Europa’s surface in color at high resolution; a future mission would include a high-resolution imaging capability to capture a much larger part of the moon’s surface. (NASA/JPL-Caltech)

The findings make it increasingly likely that there are at least two moons in our solar system that have spurting plumes of water vapor.  Saturn’s moon Enceladus definitely has plumes — the Cassini spacecraft traveled through one of them, collecting data — and now there’s good reason to conclude Europa does as well.  This raises the possibility that icy water worlds around the galaxy are spouting out their insides, and some day they might be measurable as well.

Sparks and other scientists on a NASA teleconference repeatedly emphasized, however, that more needed to be done before the presence of Europa plumes could be deemed conclusive.

“These are challenging observations pushing the limits of Hubble,” he said of their work, which used the Space Telescope Imaging Spectrograph to capture far ultraviolet radiation.

To get their results they used the “transit” method of observing Europa, a technique pioneered by exoplanet astronomers working to understand the compositions of the atmospheres of planets far, far away.  That scientists studying possible Europan plumes and methane compositions around distant planets demonstrates just how much cross pollination exists between astronomy, planetary science, astrobiology and exoplanet research have become.

“The atmosphere of an extrasolar planet blocks some of the starlight that is behind it,” Sparks explained. “If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter.”

The results were collected over a 15 month period, largely in 2014.  It took several years to process the information and check and recheck the instruments and methodologies to limit the possibility of a false positive.

The findings support earlier evidence for water plumes on Europa detected by a team led by Lorenz Roth of Southwest Research Institute in San Antonio.  They concluded that water vapor had erupted from south polar region of Europa and reached more than 100 miles into space.

Although both teams used Hubble’s Space Telescope Imaging Spectrograph (STIS) instrument, each used an independent method to arrive at the same conclusion.

 

Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of the planet. That choreography raises the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. (A. Field; STScI)
Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of the planet. That choreography raises the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. (A. Field; STScI)

Europa is cold — very cold.  The surface temperature at the equator never rises above minus 260 degrees Fahrenheit. At the poles of the moon, the temperature never rises above minus 370 F.

So how can there be a large ocean beneath the ice to begin with?

The answer involves heat produced by “flexing” of Europa based on its eccentric orbit and the gravitational pull of Jupiter.

This is how a NASA article described it:

“As Europa’s distance from Jupiter changes over the course of its orbit, Jupiter’s gravitational attraction changes, since gravitational force is dependent on distance.  As a result, the tidal bulge raised by Jupiter goes up and down. This flexing causes heating of Europa’s subsurface.”

But Europa, like Earth and every other celestial body, has also been on the receiving end over the eons of material from asteroids, comets, smaller planets and even deep space.  In addition to basic elements and compounds, Europa likely had organic material — the building blocks of life — delivered to it as well.

What’s more, the moon no doubt contains long-lived radioactive isotopes brought to it after formation. The decay of these isotopes would produce radiogenic heating, and may play a role in keeping the Europan ocean wet.

Results from prior missions strongly suggest that this water on Europa is salty, adding to the prospects for life.  And in 2016, a study suggested that Europa produces 10 times more oxygen than hydrogen, which is similar to the ratio on Earth.

 

cryovolcanoesn in europa
Scenario for getting water to Europa’s surface. Artist’s conception of ridges and fractures of Europa.  The ice cover is estimated to be between 6 and 13 miles thick. (NASA/JPL-Caltech)

So, that there may well be a habitable ocean between the ice mantle and rocky insides of Europa is well accepted.  How might some of that water rise up to the surface and ultimately erupt as a plume?

Britney Schmidt, assistant professor at the School of Earth and Atmospheric Sciences at Georgia Institute of Technology in Atlanta, said it has long been hypothesized that vents open at times between the surface and the water below — if not the oceans, then perhaps some lakes closer to the surface.

This is hypothesized to be most likely in chaos terrain, where features such as ridges, cracks, and plains (be they of ice or rock) appear jumbled and enmeshed with one another.  Europa is covered with this kind of geology.

Schmidt, who has studied Europa extensively, described the upwellings as “cryovolcanoes” — small fingers of liquid water pushed up to the surface by the intense pressure of miles of ice above these oceans.

While the presumptive plume activity appears to be most common near the south pole, it is also found elsewhere, including one detection near the equator.

 

NASA hopes the Europan Clipper will fly in the early or mid 2020s and will search for signs of habitability. It is expected to circle the moon for three years. (NASA/JPL-Caltech)
NASA hopes the Europan Clipper will fly in the early or mid 2020s and will search for signs of habitability. It is expected to circle the moon for three years. (NASA/JPL-Caltech)

Europa has been on NASA’s radar screen for some time.  The National Research Council’s once-a-decade review for planetary science, issued in 2013, made exploration of Europa the agency’s highest-priority mission in that arena. The agency generally follows the NRC recommendations.

As currently conceived, the mission would send a probe and lander to the moon, to be launched in the 2020s. Funding for the estimated $2.3 billion project remains a major issue, but last year NASA asked scientists and engineers to propose designs for instruments. Thirty-three proposals came in and nine were selected.

As it is being developed, the mission would send a solar-powered spacecraft into a long, looping orbit around Jupiter to then perform three-years of repeated close flybys of Europa. In total, the mission would perform 45 flybys at altitudes ranging from 16 miles to 1,700 miles (25 kilometers to 2,700 kilometers).

But later action in Congress — where Rep. John Culberson, a Texas Republican who represents the area including NASA headquarters,  has pushed hard for a major Europa mission — added a lander to the project, to be launched two years after the Clipper.   Culberson, chair of the House subcommittee that funds NASA, strongly believes that NASA will find the first evidence for life beyond Earth in the ocean beneath the thick surface ice.

 Rep. John Culberson, R-Texas, is chairman of the House Subcommittee on Commerce, Justice, Science, which oversees NASA funding. Culberson is a strong proponent of missions to Europa in search of extraterrestrial life. (Photo By Tom Williams/CQ Roll Call)
Rep. John Culberson, R-Texas, chairman of the House Subcommittee on Commerce, Justice, Science, is an active proponent of missions to Europa to search of extraterrestrial life. His subcommittee oversees NASA funding. (Photo By Tom Williams/CQ Roll Call)

The selected science instruments includes cameras and spectrometers to produce high-resolution images of Europa’s surface and determine its composition. An ice penetrating radar will determine the thickness of the moon’s icy shell and search for subsurface lakes similar to those beneath Antarctica. The mission also will carry a magnetometer to measure strength and direction of the moon’s magnetic field, which will allow scientists to determine the depth and salinity of its ocean.

A thermal instrument will scour Europa’s frozen surface in search of recent eruptions of warmer water, while additional instruments will search for evidence of water and tiny particles in the moon’s thin atmosphere.

Curt Niebur, project scientist for the Europa mission, was on the teleconference call as well, and described the increasing possibility that the Clipper will find Europan plumes as enormously exciting and important.  He said that the spacecraft will have the ability to change course and head to an area experiencing a plume — should one erupt.

He also said the vehicle could potentially pass through a plume like Cassini did with one of the plumes of Enceladus.  Those plumes are larger than anything tentatively detected on Europa and are more predictable in their timing and locations.

But who knows what might be possible?

“We found out a lot about Enceladus by flying through the plume and sampling plume material,” Niebur said.  “We would kill to have that kind of information for Europa.”

 

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How Will We Know What Exoplanets Look Like, and When?

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An earlier version of this article was accidently published last week before it was completed.  This is the finished version, with information from this week’s AAS annual conference.

This image of a pair of interacting galaxies called Arp 273 was released to celebrate the 21st anniversary of the launch of the NASA/ESA Hubble Space Telescope. The distorted shape of the larger of the two galaxies shows signs of tidal interactions with the smaller of the two. It is thought that the smaller galaxy has actually passed through the larger one.
This image of a pair of interacting galaxies called Arp 273 was released to celebrate the 21st anniversary of the launch of the NASA/ESA Hubble Space Telescope. The distorted shape of the larger of the two galaxies shows signs of tidal interactions with the smaller of the two. It is thought that the smaller galaxy has actually passed through the larger one.

Let’s face it:  the field of exoplanets has a significant deficit when it comes to producing drop-dead beautiful pictures.

We all know why.  Exoplanets are just too small to directly image, other than as a miniscule fraction of a pixel, or perhaps some day as a full pixel.  That leaves it up to artists, modelers and the travel poster-makers of the Jet Propulsion Lab to help the public to visualize what exoplanets might be like.  Given the dramatic successes of the Hubble Space Telescope in imaging distant galaxies, and of telescopes like those on the Cassini mission to Saturn and the Mars Reconnaissance Orbiter, this is no small competitive disadvantage.  And this explains why the first picture of this column has nothing to do with exoplanets (though billions of them are no doubt hidden in the image somewhere.)

The problem is all too apparent in these two images of Pluto — one taken by the Hubble and the other by New Horizons telescope as the satellite zipped by.

 

image

Pluto image taken by Hubble Space Telescope (above) and close up taken by New Horizons in 2015. (NASA)
Pluto image taken by Hubble Space Telescope (above) and close up taken by New Horizons in 2015. (NASA)

 

Pluto is about 4.7 billion miles away.  The nearest star, and as a result the nearest possible planet, is 25 trillion miles  away.  Putting aside for a minute the very difficult problem of blocking out the overwhelming luminosity of a star being cross by the orbiting planet you want to image,  you still have an enormous challenge in terms of resolving an image from that far away.

While current detection methods have been successful in confirming more than 2,000 exoplanets in the past 20 years (with another 2,000-plus candidates awaiting confirmation or rejection),  they have been extremely limited in terms of actually producing images of those planetary fireflies in very distant headlights.  And absent direct images — or more precisely, light from those planets — the amount of information gleaned about the chemical makeup of their atmospheres  as been limited, too.

But despite the enormous difficulties, astronomers and astrophysicist are making some progress in their quest to do what was considered impossible not that long ago, and directly image exoplanets.

In fact, that direct imaging — capturing light coming directly from the sources — is pretty uniformly embraced as the essential key to understanding the compositions and dynamics of exoplanets.  That direct light may not produce a picture of even a very fuzzy exoplanet for a very long time to come, but it will definitely provide spectra that scientists can read to learn what molecules are present in the atmospheres, what might be on the surfaces and as a result if there might be signs of life.

This diagram illustrates how astronomers using NASA's Spitzer Space Telescope can capture the elusive spectra of hot-Jupiter planets. Spectra are an object's light spread apart into its basic components, or wavelengths. By dissecting light in this way, scientists can sort through it and uncover clues about the composition of the object giving off the light. To obtain a spectrum for an object, one first needs to capture its light. Hot-Jupiter planets are so close to their stars that even the most powerful telescopes can't distinguish their light from the light of their much brighter stars. But, there are a few planetary systems that allow astronomers to measure the light from just the planet by using a clever technique. Such "transiting" systems are oriented in such a way that, from our vantage point, the planets' orbits are seen edge-on and cross directly in front of and behind their stars. In this technique, known as the secondary eclipse method, changes in the total infrared light from a star system are measured as its planet transits behind the star, vanishing from our Earthly point of view. The dip in observed light can then be attributed to the planet alone. To capture a spectrum of the planet, Spitzer must observe the system twice. It takes a spectrum of the star together with the planet (first panel), then, as the planet disappears from view, a spectrum of just the star (second panel). By subtracting the star's spectrum from the combined spectrum of the star plus the planet, it is able to get the spectrum for just the planet (third panel). This ground-breaking technique was used by Spitzer to obtain the first-ever spectra of two planets beyond our solar system, HD 209458b and HD 189733b. The results suggest that the hot planets are socked in with dry clouds high up in the planet's stratospheres. In addition, HD 209458b showed hints of silicates, indicating those high clouds might be made of very fine sand-like particles.
This diagram illustrates how astronomers using NASA’s Spitzer Space Telescope can capture the elusive spectra of hot-Jupiter planets. Spectra are an object’s light spread apart into its basic components, or wavelengths. By dissecting light in this way, scientists can sort through it and uncover clues about the composition of the object giving off the light. (NASA/JPL-Caltech)

There has been lots of technical and scientific debate about how to capture that light, as well as debate about how to convince Congress and NASA to fund the search.  What’s more, the exoplanet community has a history of fractious internal debate and competition that has at times undermined its goals and efforts, and that has been another hotly discussed subject.  (The image of a circular firing squad used to be a pretty common one for the community.)

But a seemingly much more orderly strategy has been developed in recently years and was on display at the just-completed American Astronomical Society annual meeting in Florida.  The most significant breaking news was probably that NASA has gotten additional funds to support a major exoplanet direct imaging mission in the 2020s, the Wide Field Infrared Survey Telescope (WFIRST), and that the agency is moving ahead with a competition between four even bigger exoplanet or astrophysical missions for the 2030s. The director of NASA Astrophysics, Paul Hertz, made the formal announcements during the conference, when he called for the formation of four Science and Technology Definition Teams to assess in great detail the potentials and plausibilities of the four possibilities.

Paul Hertz, Director of the Astrophysics Division of NASA's Science Mission Directorate.
Paul Hertz, Director of the Astrophysics Division of NASA’s Science Mission Directorate.

Putting it into a broader perspective, astronomer Natalie Batalha, science lead for the Kepler Space Telescope, told a conference session on next-generation direct imaging that  “with modern technology, we don’t have the capability to image a solar system analog.”  But, she said, “that’s where we want to go.”

And the road to discovering exoplanets that might actually sustain life may well require a space-based telescope in the range of eight to twelve meters in radius, she and others are convinced.  Considering that a very big challenge faced by the engineers of the James Webb Space Telescope (scheduled to launch in 2018) was how to send a 6.5 meter-wide mirror into space, the challenges (and the costs) for a substantially larger space telescope will be enormous.

We will come back in following post to some of these plans for exoplanet missions in the decades ahead, but first let’s look at a sample of the related work done in recent years and what might become possible before the 2020s.  And since direct imaging is all about “seeing” a planet — rather than inferring its existence through dips in starlight when an exoplanet transits, or the wobble of a sun caused by the presence of  an orbiting ball of rock (or gas)  — showing some of the images produced so far seems appropriate.  They may not be breath-taking aesthetically, but they are remarkable.

There is some debate and controversy over which planets were the first to be directly imaged. But all agree that a major breakthrough came in 2008 with the imaging of the HR8799 system via ground-based observations.

NASA/JPL-Caltech/Palomar Observatory - http://www.nasa.gov/topics/universe/features/exoplanet20100414-a.html This image shows the light from three planets orbiting a star 120 light-years away. The planets' star, called HR8799, is located at the spot marked with an "X." This picture was taken using a small, 1.5-meter (4.9-foot) portion of the Palomar Observatory's Hale Telescope, north of San Diego, Calif. This is the first time a picture of planets beyond our solar system has been captured using a telescope with a modest-sized mirror -- previous images were taken using larger telescopes. The three planets, called HR8799b, c and d, are thought to be gas giants like Jupiter, but more massive. They orbit their host star at roughly 24, 38 and 68 times the distance between our Earth and sun, respectively (Jupiter resides at about 5 times the Earth-sun distance).
This 2010 image shows the light from three planets orbiting HR8799, 120 light-years away.  The three planets, called HR8799b, c and d, are thought to be gas giants like Jupiter, but more massive. (NASA/JPL-Caltech/Palomar Observatory)

First, three Jupiter-plus gas giants were identified using the powerful Keck and Gemini North infrared telescopes on Mauna Kea in Hawaii by a team led by Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics. That detection was followed several years later the discovery of a fourth planet and then by the release of the surprising image above, produced with the quite small (4.9 foot) Hale telescope at the Palomar Observatory outside of San Diego.

As is the case for all planets directly imaged, the “pictures” were not taken as we would with our own cameras, but rather represent images produced with information that is crunched in a variety of necessary technical ways before their release.  Nonetheless, they are images in a way similar the iconic Hubble images that also need a number of translating steps to come alive.

Because light from the host star has to be blocked out for direct imaging to work, the technique now identifies only planets with very long orbits. In the case of HR8799, the planets orbit respectively at roughly 24, 38 and 68 times the distance between our Earth and sun.  Jupiter orbits at about 5 times the Earth-sun distance.

In the same month as the HR8799 announcement, another milestone was made public with the detection of a planet orbiting the star Formalhaut.  That, too, was done via direct imagining, this time with the Hubble Space Telescope.

 

The Hubble images were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The planet will appear to cross a vast belt of debris around the star roughly 20 years from now. If the planet's orbit lies in the same plane with the belt, icy and rocky debris in the belt could crash into the planet's atmosphere and produce various phenomena. The black circle at the center of the image blocks out the light from the bright star, allowing reflected light from the belt and planet to be photographed. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)
The Hubble images the the star Formalhaut and planet Formalhaut b were taken with the Space Telescope Imaging Spectrograph in 2010 and 2012. This false-color composite image reveals the orbital motion of the Fomalhaut b. Based on these observations, astronomers calculated that the planet is in a 2,000-year-long, highly elliptical orbit. The black circle at the center of the image blocks out light from the very bright star, allowed reflected light from the belt and planet to be captured.  Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)

 

Signs of the planet were first detected in 2004 and 2006 by a group headed by Paul Kalas at the University of California, Berkeley, and they made the announcement in 2008.  The discovery was confirmed several years later and tantalizing planetary dynamics began to emerge from the images (all in false color.) For instance, the planet appears to be on a path to cross a vast belt of debris around the star roughly 20 years from now.  If the planet’s orbit lies in the same plane with the belt, icy and rocky debris could crash into the planet’s atmosphere and cause interesting damage.

The region around Fomalhaut’s location is black because astronomers used a coronagraph to block out the star’s bright glare so that the dim planet could be seen. This is essential since Fomalhaut b is 1 billion times fainter than its star. The radial streaks are scattered starlight. Like all the planets detected so far using some form of direct imaging,  Fomalhaut b if far from its host star and completes an orbit every 872 years.

Adaptive optics of the Gemini Planet Imager, at the Gemini South Observatory in Chile, has been successful in imaging exoplanets as well.  The GPI grew out of a proposal by the Center for Adaptive Optics, now run by the University of California system, to inspire and see developed innovative optical technology.  Some of the same breakthroughs now used in treating human eyes found their place in exoplanet astronomy.

 

Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).
Discovery image of 51 Eri b with the Gemini Planet Imager taken in the near-infrared light on December 18, 2014. The bright central star has been mostly removed by a hardware and software mask to enable the detection of the exoplanet one million times fainter. Credits: J. Rameau (UdeM) and C. Marois (NRC Herzberg).

The Imager, which began operation in 2014, was specifically created to discern and evaluate dim, newer planets orbiting bright stars using a different kind of direct imaging. It is adept at detecting young planets, for instance, because they still retain heat from their formation, remain luminous and visible. Using the GPI to study the area around the y0ung (20-million-year-old) star 51 Eridiani, the team made their first exoplanet discovery in 2014.

By studying its thermal emissions, the team gained insights into the planet’s atmospheric composition and found that — much like Jupiter’s — it is dominated by methane.  To date, methane signatures have been weak or absent in directly imaged exoplanets.

James Graham, an astronomer at the University of California, Berkeley, is the project leader for a three-year GPI survey of 600 stars to find young gas giant planets, Jupiter-size and above.

“The key motivation for the experiment is that if you can detect heat from the planet, if you can directly image it, then by using basic science you can learn about formation processes for these planets.”  So by imaging the planets using these very sophisticated optical advances, scientists go well beyond detecting exoplanets to potentially unraveling deep mysteries (even if we still won’t know what the planets “look like” from an image-of-the-day perspective.

The GPI has also detected a second exoplanet, shown here at different stages of its orbit:

 

The animation is a series of images taken between November 2013 and April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile, and shows the exoplanet β Pictoris b, which is more than 60 lightyears from Earth. The star is the black area on the left edge of the frame and is hidden by the Gemini Planet Imager’s coronagraph. We are looking at the planet’s orbit almost edge-on, with the planet closer to the Earth than the star. (M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute)
The animation is a series of images taken between November 2013 and April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile, and shows the exoplanet β Pictoris b, which is more than 60 lightyears from Earth. The star is the black area on the left edge of the frame and is hidden by the Gemini Planet Imager’s coronagraph. (M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute)

A next big step in direct imaging of exoplanets will come with the launch of the James Webb Space Telescope in 2018.  While not initially designed to study exoplanets — in fact, exoplanets were just first getting discovered when the telescope was under early development — it does now include a coronagraph which will substantially increase its usefulness in imaging exoplanets.

As explained by Joel Green, a project scientist for the Webb at the Space Telescope Science Institute in Baltimore, the new observatory will be able to capture light — in the form of infrared radiation– that will be coming from more distant and much colder environments than what Hubble can probe.

“It’s sensitive to dimmer things, smaller planets that are more earth-sized.  And because it can see fainter objects, it will be more help in understanding the demographics of exoplanets.  It uses the infrared region of the spectrum, and so it can look better into the cloud levels of the planets than any telescope so far and see deeper.”

James Webb Space Telescope mirror being inspected at Goddard Space Flight Center, as it nears completion. The powerful, sophisticated and long-awaited telescope is scheduled to launch in 2018.
James Webb Space Telescope mirror being inspected at Goddard Space Flight Center, as it nears completion. The powerful, sophisticated and long-awaited telescope is scheduled to launch in 2018.

These capabilities and more are going to be a boon to exoplanet researchers and will no doubt advance the direct imaging effort and potentially change basic understandings about exoplanets.  But it is not expected produce gorgeous or bizarre exoplanet pictures for the public, as Hubble did for galaxies and nebulae.  Indeed, unlike the Hubble — which sees primarily in visible light —  Webb sees in what Green said is, in effect, night vision.   And so researchers are still working on how they will produce credible images using the information from Webb’s infrared cameras and translating them via a color scheme into pictures for scientists and the public.

Another compelling exoplanet-imaging technology under study by NASA is the starshade, or external occulter, a metal disk in the shape of a sunflower that might some day be used to block out light from host stars in order to get a look at faraway orbiting planets.  MIT’s Sara Seager led a NASA study team that reported back on the starshade last year in a report that concluded it was technologically possible to build and launch, and would be scientifically most useful.  If approved, the starshade — potentially 100 feet across — could be used with the WFIRST telescope in the 2020s.  The two components would fly far separately, as much as 35,000 miles away from each other, and together could produce breakthrough exoplanet direct images.

An artist's depiction of a sunflower-shaped starshade that could help space telescopes find and characterize alien planets. Credit: NASA/JPL/Caltec
An artist’s depiction of a sunflower-shaped starshade that could help space telescopes find and characterize alien planets.  Credit: NASA/JPL/Caltech

Here is a link to an animation of the starshade being deployed: http://planetquest.jpl.nasa.gov/video/15

The answer, then, to the question posed in the title to this post — “How Will We Know What Exoplanets Look Like, and When?”– is complex, evolving and involves a science-based definition of what “looking like” means.  It would be wonderful to have images of exoplanets that show cloud formations, dust and maybe some surface features, but “direct imaging” is really about something different.  It’s about getting light from exoplanets that can tell scientists about the make-up of those exoplanets and their atmospheres, and ultimately that’s a lot more significant than any stunning or eerie picture.

And with that difference between beauty and science in mind, this last image is one of the more striking ones I’ve seen in some time.

Moon glow over Las Campanas Observatory, run by the Carnegie Institution of Science, in Chile. (Yuri Beretsky)
Moon glow over Las Campanas Observatory, operated by the Carnegie Institution of Science, in Chile. (Yuri Beretsky)

It was taken at the Las Campanas Observatory in Chile last year, during a night of stargazing.  Although the observatory is in the Atacama Desert, enough moisture was present in the atmosphere to create this lovely moon-glow.

But working in the observatory that night was Carnegie’s pioneer planet hunter Paul Butler, who uses the radial velocity method to detect exoplanets.  But to do that he needs to capture light from those distant systems.  So the night — despite the beautiful moon-glow — was scientifically useless.

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