Worlds within Worlds: Hubble Peels Back the Layers of a Warm Neptune

Take Neptune for example. For many years, especially since 1989 when Voyager 2 flew past Neptune and measured its gravity field, astronomers have known that the blue giant harbors a secret world inside. Hidden deep below the azure cloud tops lies a rocky core not much larger than Earth. Uranus has one, too! These “worlds within worlds” could have exotic properties including scorching hot oceans and diamond rain.

If only researchers could peel back the clouds for a closer look….

Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b. The planet’s atmosphere is evaporating because of extreme irradiation from its parent star. Sciencecast Video

About 30 light years away, a Neptune-sized planetis having some of its layers peeled back.

Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b.

“This cloud is spectacular,” says the study’s leader, David Ehrenreich of the Observatory of the University of Geneva in Switzerland. “The research team has nicknamed it ‘The Behemoth.’”

The planet’s atmosphere is evaporating because of extreme irradiation from its parent star—a process that might have been even more intense in the past.

“The parent star, which is a faint red dwarf, was once more active,” says Ehrenreich. “This means that the planet’s atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that the planet may have lost up to 10 percent of its atmosphere.”

GJ 436b is considered to be a “Warm Neptune” because of its size and because it is much closer to its parent star than Neptune is to our own sun. Orbiting at a distance of less than 3 million miles, It whips around the central red dwarf in just 2.6 Earth days. For comparison, the Earth is 93 million miles from the sun and orbits it every 365.24 days.

Systems like GJ 436b could explain the existence of so-called “Hot Super-Earths.”

“Hot Super-Earths” are larger, hotter versions of our own planet. Space telescopes such as NASA’s Kepler and the French led CoRoT have discovered hundredsof them orbiting distant stars. The existence of The Behemoth suggests that Hot Super-Earths could be the remnants of Warm Neptunes that completely lost their gaseous atmospheres to evaporation.

Finding a cloud around GJ 436b required Hubble’s ultraviolet vision. Earth’s atmosphere blocks most ultraviolet light so only a space telescope like Hubble could make the crucial observations.

“You would not see The Behemoth in visible wavelengths because it is optically transparent,” says Ehrenreich. On the other hand, it is opaque to UV rays. “So when you turn the ultraviolet eye of Hubble onto the system, it’s really kind of a transformation because the planet turns into a monstrous thing.”

The ultraviolet technique could be a game-changer in exoplanet studies, he adds. Ehrenreich expects that astronomers will find thousands of Warm Neptunes and Super-Earths in the years ahead. 

Astronomers will want to examine them for evidence of evaporation. Moreover, the ultraviolet technique might be able to spot the signature of oceans evaporating on Earth-like planets, shedding new light on worlds akin to our own.

Maybe you can’t judge a book by its cover, but you can judge a planet by its Behemoth.

Source: NASA Science News

Hubble Sees a 'Behemoth' Bleeding Atmosphere Around a Warm Neptune-Sized Exoplanet Artist's Concept of Extasolar Planet GJ 436b

 Artist's Concept of Extasolar Planet GJ 436b

This artist's concept shows "The Behemoth," an enormous comet-like cloud of hydrogen bleeding off of a warm, Neptune-sized planet just 30 light-years from Earth. Also depicted is the parent star, which is a faint red dwarf named GJ 436. The hydrogen is evaporating from the planet due to extreme radiation from the star. A phenomenon this large has never before been seen around any exoplanet. Credit: NASA, ESA, and G. Bacon (STScI)

Polar View of GJ 436b System

This artist's diagram shows a polar view of the GJ 436 system. The warm, Neptune-sized exoplanet GJ 436b resides very close to its star — less than 3 million miles — and whips around it in just 2.6 Earth days. A huge, comet-like cloud of hydrogen nicknamed "The Behemoth" is shown bleeding off of the planet and trailing it like the tail of a comet.The planet is just 30 light-years from Earth. Credit: NASA, ESA, and A. Feild (STScI)

Photometry of Transiting Planet GJ 436b

This artist's diagram shows the unusual light curve produced when the exoplanet GJ 436b and the huge, comet-like hydrogen cloud nicknamed "The Behemoth" pass in front of the parent star. Because the planet's orbit is tilted nearly edge-on to our view from Earth, the planet and cloud can be seen eclipsing its star. Astronomers see the extended dip in the light caused by the enormous cloud. That dip trails off slowly due to the cloud's comet-like tail. Credit: NASA, ESA, and A. Feild (STScI). 

Released Images

Astronomers using NASA's Hubble Space Telescope have discovered an immense cloud of hydrogen dubbed "The Behemoth" bleeding off a planet orbiting a nearby star. The enormous, comet-like feature is about 50 times the size of the parent star. The hydrogen is evaporating from a warm, Neptune-sized planet, due to extreme radiation from the star. A phenomenon this large has never before been seen around any exoplanet. Given this planet's small size, it may offer clues to how Hot Super-Earths — massive, rocky, hot versions of Earth — are born around other stars through the evaporation of their outer layers of hydrogen. 

"This cloud is very spectacular, though the evaporation rate does not threaten the planet right now," explains the study's leader, David Ehrenreich of the Observatory of the University of Geneva in Switzerland. "But we know that in the past, the star, which is a faint red dwarf, was more active. This means that the planet evaporated faster during its first billion years of existence. Overall, we estimate that it may have lost up to 10 percent of its atmosphere." The planet, named GJ 436b, is considered to be a "Warm Neptune," because of its size and it is much closer to its star than Neptune is to our sun. Although it is in no danger of having its atmosphere completely evaporated and being stripped down to a rocky core, this planet could explain the existence of so-called Hot Super-Earths that are very close to their stars.

These hot, rocky worlds were discovered by the Convection Rotation and Planetary Transits (CoRoT) spacecraft (led by the French Space Agency (CNES) in collaboration with ESA (the European Space Agency), and several other international partners), and NASA's Kepler space telescope. Hot Super-Earths could be the remnants of more massive planets that completely lost their thick, gaseous atmospheres to the same type of evaporation.

Because Earth's atmosphere blocks most ultraviolet light, astronomers needed a space telescope with Hubble's ultraviolet capability and exquisite precision to find "The Behemoth."

"You would have to have Hubble's eyes," says Ehrenreich. "You would not see it in visible wavelengths. But when you turn the ultraviolet eye of Hubble onto the system, it's really kind of a transformation, because the planet turns into a monstrous thing."

Because the planet's orbit is tilted nearly edge-on to our view from Earth, the planet can be seen passing in front of its star. Astronomers also saw the star eclipsed by "The Behemoth" hydrogen cloud around the planet.

Ehrenreich and his team think that such a huge cloud of gas can exist around this planet because the cloud is not rapidly heated and swept away by the radiation pressure from the relatively cool red dwarf star. This allows the cloud to stick around for a longer time. The team's findings will be published in the June 25 edition of the journal Nature.

Evaporation such as this may have happened in the earlier stages of our own solar system, when Earth had a hydrogen-rich atmosphere that dissipated over 100 million to 500 million years. If so, Earth may previously have sported a comet-like tail. It's also possible it could happen to Earth's atmosphere at the end of our planet's life, when the sun swells up to become a red giant and boils off our remaining atmosphere, before engulfing our planet completely.

GJ 436b resides very close to its star — less than 3 million miles — and whips around it in just 2.6 Earth days. (In comparison, Earth is 93 million miles from our sun and orbits it every 365.24 days.) This exoplanet is at least 6 billion years old, and may even be twice that age. It has a mass of around 23 Earths. At just 30 light-years from Earth, it's one of the closest known extrasolar planets.

Finding "The Behemoth" could be a game-changer for characterizing atmospheres of the whole population of Neptune-sized planets and Super-Earths in ultraviolet observations. In the coming years, Ehrenreich expects that astronomers will find thousands of this kind of planet.

The ultraviolet technique used in this study also may spot the signature of oceans evaporating on smaller, more Earth-like planets. It will be extremely challenging for astronomers to directly see water vapor on those worlds, because it's too low in the atmosphere and shielded from telescopes. However, when water molecules are broken by the stellar radiation into hydrogen and oxygen, the relatively light hydrogen atoms can escape the planet. If scientists could spot this hydrogen evaporating from a planet that is a bit more temperate and little less massive than GJ 436b, that is a good sign of an ocean on the surface.

Other related links:

•  Science Paper by: D. Ehrenreich et al. (PDF document)
• Hubble-Europe's Release
• NASA's Hubble Portal

Contact:

Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

David Ehrenreich
University of Geneva, Geneva, Switzerland
011-41-22-379-2390
david.ehrenreich@unige.ch

Source: HubbleSite

Helium-Shrouded Planets May Be Common in Our Galaxy

Planets having atmospheres rich in helium may be common in our galaxy, according to a new theory based on data from NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech. › Full image and caption

This diagram illustrates how hypothetical helium atmospheres might form. These would be on planets about the mass of Neptune, or smaller, which orbit tightly to their stars, whipping around in just days. Image credit: NASA/JPL-Caltech › Full image and caption

They wouldn't float like balloons or give you the chance to talk in high, squeaky voices, but planets with helium skies may constitute an exotic planetary class in our Milky Way galaxy. Researchers using data from NASA's Spitzer Space Telescope propose that warm Neptune-size planets with clouds of helium may be strewn about the galaxy by the thousands.

"We don't have any planets like this in our own solar system," said Renyu Hu, NASA Hubble Fellow at the agency's Jet Propulsion Laboratory in Pasadena, California, and lead author of a new study on the findings accepted for publication in the Astrophysical Journal. "But we think planets with helium atmospheres could be common around other stars."

Prior to the study, astronomers had been investigating a surprising number of so-called warm Neptunes in our galaxy. NASA's Kepler space telescope has found hundreds of candidate planets that fall into this category. They are the size of Neptune or smaller, with tight orbits that are closer to their stars than our own sizzling Mercury is to our sun. These planets reach temperatures of more than 1,340 degrees Fahrenheit (1,000 Kelvin), and orbit their stars in as little as one or two days.

In the new study, Hu and his team make the case that some warm Neptunes -- and warm sub-Neptunes, which are smaller than Neptune -- could have atmospheres enriched with helium. They say that the close proximity of these planets to their searing stars would cause the hydrogen in their atmospheres to boil off.

"Hydrogen is four times lighter than helium, so it would slowly disappear from the planets' atmospheres, causing them to become more concentrated with helium over time," said Hu. "The process would be gradual, taking up to 10 billion years to complete." For reference, our planet Earth is about 4.5 billion years old.

Warm Neptunes are thought to have either rocky or liquid cores, surrounded by gas. If helium is indeed the dominant component in their atmospheres, the planets would appear white or gray. By contrast, the Neptune of our own solar system is a brilliant azure blue. The methane in its atmosphere absorbs the color red, giving Neptune its blue hue.

A lack of methane in one particular warm Neptune, called GJ 436b, is in fact what led Hu and his team to develop their helium planet theory. Spitzer had previously observed GJ 436b, located 33 light-years away, and found evidence for carbon but not methane. This was puzzling to scientists, because methane molecules are made of one carbon and four hydrogen atoms, and planets like this are expected to have a lot of hydrogen. Why wasn't the hydrogen linking up with carbon to produce methane?

According to the new study, the hydrogen might have been slow-cooked off the planet by radiation from the host stars. With less hydrogen around, the carbon would pair up with oxygen to make carbon monoxide. In fact, Spitzer found evidence for a predominance of carbon monoxide in the atmosphere of GJ 436b. The next step to test this theory is to look at other warm Neptunes for signs of carbon monoxide and carbon dioxide, which are indicators of helium atmospheres. The team says this might be possible with the help of NASA's Hubble Space Telescope, and NASA's upcoming James Webb Space Telescope may one day directly detect that helium.

Meanwhile, the wacky world of exoplanets continues to surprise astronomers.

"Any planet one can imagine probably exists, out there, somewhere, as long as it fits within the laws of physics and chemistry," said co-author Sara Seager of the Massachusetts Institute of Technology in Cambridge and JPL. "Planets are so incredibly diverse in their masses, sizes and orbits that we expect this to extend to exoplanet atmospheres."

A third author of the paper is Yuk Yung of the California Institute of Technology in Pasadena and JPL.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information on Spitzer, visit: http://spitzer.caltech.edu - http://www.nasa.gov/spitzer

Media Contact 

 Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov

Source: JPL-Caltech

Hubble Sees Cloudy Super-Worlds with Chance for More Clouds

Clouds in Atmosphere of Exoplanet GJ 1214b (Artist's View)

Artwork Credit: NASA, ESA, and G. Bacon (STScI)

Science Credit: NASA, ESA, L. Kreidberg and J. Bean (University of Chicago), 
and H. Knutson (California Institute of Technology)
Highest-quality download options 

Planet Comparison Graphic (Illustration)

Credit: NASA, ESA, and A. Feild and G. Bacon (STScI)

Highest-quality download options 

Weather forecasters on exoplanet GJ 1214b would have an easy job. Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more clouds.

Two teams of scientists using NASA's Hubble Space Telescope report they have characterized the atmospheres of a pair of planets with masses intermediate between gas giants, like Jupiter, and smaller, rockier planets, like Earth. A survey by NASA's Kepler space telescope mission showed that objects in this size range are among the most common type of planets in our Milky Way galaxy. The researchers described their work as an important milestone on the road to characterizing potentially habitable, Earth-like worlds beyond the solar system.

The findings appear in separate papers in the January 2 issue of the journal Nature.

The two planets studied are known as GJ 436b and GJ 1214b. GJ 436b is categorized as a "warm Neptune" because it is much closer to its star than frigid Neptune is to our Sun. The planet is located 36 light-years away in the constellation Leo.

GJ 1214b is known as a "super-Earth" type planet. Super-Earths are planets with masses between that of Earth and Neptune. Because no such planet exists in our solar system, the physical nature of super-Earths is largely unknown. GJ1214b is located just 40 light-years from Earth, in the constellation Ophiuchus.

Both GJ 436b and GJ 1214b can be observed passing in front of, or transiting, their parent stars. This provides an opportunity to study these planets in more detail as starlight filters through their atmospheres.

An atmospheric study of GJ 436b based on such transit observations with Hubble over the last year is presented in one of the papers, led by Heather Knutson of the California Institute of Technology in Pasadena, Calif. The news is about what they didn't find. The Hubble spectra were featureless and revealed no chemical fingerprints whatsoever in the planet's atmosphere. "Either this planet has a high cloud layer obscuring the view, or it has a cloud-free atmosphere that is deficient in hydrogen, which would make it very unlike Neptune," said Knutson. "Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapor, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures."

Observations similar to those obtained for GJ 436b had been previously obtained for GJ 1214b. The first spectra of this planet were also featureless and presented a similar puzzle: The planet's atmosphere either was predominantly water vapor or hydrogen-dominated with high-altitude clouds.

A team of astronomers led by Laura Kreidberg and Jacob Bean of the University of Chicago used Hubble to obtain a deeper view of GJ 1214b that revealed what they consider definitive evidence of high clouds blanketing the planet. These clouds hide any information about the composition and behavior of the lower atmosphere and surface. The new Hubble spectra also revealed no chemical fingerprints whatsoever in the planet's atmosphere, but the high precision of the new data enabled them to rule out cloud-free compositions of water vapor, methane, nitrogen, carbon monoxide, or carbon dioxide for the first time.

"Both planets are telling us something about the diversity of planet types that occur outside of our own solar system; in this case we are discovering that we may not know them as well as we thought," said Knutson. "We'd really like to determine the size at which these planets transition from looking like mini-gas giants to something more like a water world or a rocky, scaled-up version of the Earth. Both of these observations are fundamentally trying to answer that question."

Models of GJ 436b and GJ 1214b predict clouds that could be made out of potassium chloride or zinc sulfide at the scorching temperatures of several hundred degrees Fahrenheit predicted to be found in these atmospheres. "You would expect very different kinds of clouds to form on these planets than you would find, say, on Earth," said Kreidberg.

The Chicago team had to make a big effort to conclusively determine the nature of GJ 1214b's cloudy atmosphere. Kreidberg explained, "We really pushed the limits of what is possible with Hubble to make this measurement — our work devoted more Hubble time to a single exoplanet than ever before. This advance lays the foundation for characterizing other Earths with similar techniques." Added Bean, "I think it's very exciting that we can use a telescope like Hubble that was never designed with this in mind, do these kinds of observations with such exquisite precision, and really nail down some aspect of a super-Earth atmosphere."

Knutson continued, "For exoplanets, clouds are incredibly frustrating because they can hide the bulk composition of the atmosphere that we want to measure." However, more will be learned with the launch of the James Webb Space Telescope later this decade. Said Kreidberg, "Looking forward, the James Webb Space Telescope will be transformative. The new capabilities of this telescope will allow us to peer through the clouds on GJ 1214b and similar exoplanets."

CONTACT

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

'This Planet Tastes Funny,' According to Spitzer Telescope

The planet illustrated here, called GJ 436b

An unusual, methane-free world is partially eclipsed by its star in this artist's concept. NASA's Spitzer Space Telescope has found evidence that a hot, Neptune-sized planet orbiting a star beyond our sun lacks methane -- an ingredient common to many planets in our own solar system.

These plots from NASA's Spitzer Space Telescope show light from a distant planet, GJ 436b, and its star, as measured at six different infrared wavelengths. Astronomers use telescopes like Spitzer to measure the direct light of distant worlds, called exoplanets, and learn more about chemicals in their atmospheres.

The technique involves measuring light from an exoplanet and its star before, during and after the planet circles behind the star. (The technique only works for those planets that happen to cross behind and in front of their stars as seen from our point of view on Earth.) When the planet disappears behind the star, the total light observed drops, as seen by the dips in these light curves. This same measurement is repeated at different wavelengths of light. In this graph, the different wavelengths are on the vertical axis, and time on the horizontal axis. Those dips in the total light tell astronomers exactly how much light is coming from the planet itself.

As the data demonstrate, the amount of light coming off a planet changes with different wavelengths. The differences are due to the temperature of a planet as well as its chemical makeup. In this case, astronomers were able to show that GJ 436b lacks the common planetary ingredient of methane.

PASADENA, Calif. - NASA's Spitzer Space Telescope has discovered something odd about a distant planet -- it lacks methane, an ingredient common to many of the planets in our solar system.

"It's a big puzzle," said Kevin Stevenson, a planetary sciences graduate student at the University of Central Florida in Orlando, lead author of a study appearing tomorrow, April 22 in the journal Nature. "Models tell us that the carbon in this planet should be in the form of methane. Theorists are going to be quite busy trying to figure this one out."

The discovery brings astronomers one step closer to probing the atmospheres of distant planets the size of Earth. The methane-free planet, called GJ 436b, is about the size of Neptune, making it the smallest distant planet that any telescope has successfully "tasted," or analyzed. Eventually, a larger space telescope could use the same kind of technique to search smaller, Earth-like worlds for methane and other chemical signs of life, such as water, oxygen and carbon dioxide.

"Ultimately, we want to find biosignatures on a small, rocky world. Oxygen, especially with even a little methane, would tell us that we humans might not be alone," said Stevenson.

"In this case, we expected to find methane not because of the presence of life, but because of the planet's chemistry. This type of planet should have cooked up methane. It's like dipping bread into beaten eggs, frying it, and getting oatmeal in the end," said Joseph Harrington of the University of Central Florida, the principal investigator of the research.

Methane is present on our life-bearing planet, manufactured primarily by microbes living in cows and soaking in waterlogged rice fields. All of the giant planets in our solar system have methane too, despite their lack of cows. Neptune is blue because of this chemical, which absorbs red light. Methane is a common ingredient of relatively cool bodies, including "failed" stars, which are called brown dwarfs.

In fact, any world with the common atmospheric mix of hydrogen, carbon and oxygen, and a temperature up to 1,000 Kelvin (1,340 degrees Fahrenheit) is expected to have a large amount of methane and a small amount of carbon monoxide. The carbon should "prefer" to be in the form of methane at these temperatures.

At 800 Kelvin (or 980 degrees Fahrenheit), GJ 436b is supposed to have abundant methane and little carbon monoxide. Spitzer observations have shown the opposite. The space telescope has captured the planet's light in six infrared wavelengths, showing evidence for carbon monoxide but not methane.

"We're scratching our heads," said Harrington. "But what this does tell us is that there is room for improvement in our models. Now we have actual data on faraway planets that will teach us what's really going on in their atmospheres."

GJ 436b is located 33 light-years away in the constellation Leo, the Lion. It rides in a tight, 2.64-day orbit around its small star, an "M-dwarf" much cooler than our sun. The planet transits, or crosses in front of, its star as viewed from Earth.

Spitzer was able to detect the faint glow of GJ 436b by watching it slip behind its star, an event called a secondary eclipse. As the planet disappears, the total light observed from the star system drops -- this drop is then measured to find the brightness of the planet at various wavelengths. The technique, first pioneered by Spitzer in 2005, has since been used to measure atmospheric components of several Jupiter-sized exoplanets, the so-called "hot Jupiters," and now the Neptune-sized GJ 436b.

"The Spitzer technique is being pushed to smaller, cooler planets more like our Earth than the previously studied hot Jupiters," said Charles Beichman, director of NASA's Exoplanet Science Institute at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif. "In coming years, we can expect that a space telescope could characterize the atmosphere of a rocky planet a few times the size of the Earth. Such a planet might show signposts of life."

This research was performed before Spitzer ran out of its liquid coolant in May 2009, officially beginning its "warm" mission.

Other authors include: Sarah Nymeyer, William C. Bowman, Ryan A. Hardy and Nate B. Lust from the University of Central Florida; Nikku Madhusudhan and Sara Seager of the Massachusetts Institute of Technology, Cambridge; Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md.; and Emily Rauscher of Columbia University, New York.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .