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article imageAstronomy first as cloudy weather revealed on alien world

By Robert Myles     Jan 2, 2014 in Science
Chicago - Thanks to the Hubble Space Telescope, a team of scientists, led by researchers in the Department of Astronomy and Astrophysics at the University of Chicago, have achieved an astronomical first.
The UChicago-led researchers have characterized the atmosphere of a super-Earth exoplanet orbiting a distant star.
But the researchers’ meteorological prediction for exoplanet GJ 1214b, located 40 light years from Earth in the direction of the constellation Ophiuchus, is uncompromisingly gloomy: It’ll be cloudy today, tomorrow, next week, next month; for, GJ 1214b is a planet permanently swathed in clouds blanketing the surface below.
The findings are nonetheless significant since the researchers squeezed the resources of the Hubble Space Telescope to their limits during 96 hours of telescope time spread over 11 months—the largest Hubble program ever undertaken dedicated to a single exoplanet.
With Hubble now approaching a quarter of a century in Earth orbit — it was launched on April 24, 1990 — details of exoplanet GJ 1214b’s atmosphere offer a tantalizing glimpse of the further discoveries in prospect once a series of new space telescopes begin returning data.
This rendering shows the size of GJ 1214b and another  larger exoplanet compared to Earth and Neptun...
This rendering shows the size of GJ 1214b and another, larger exoplanet compared to Earth and Neptune. Researchers used the Hubble Space Telescope to reveal cloudy weather on the alien world of GJ 1214b.
Exoplanet GJ 1214b is classified as a super-Earth type planet, meaning that its mass is between that of Earth (diameter 12,742 kilometers) and that of gas giant Neptune (49,244 kilometers). As more exoplanets have been catalogued, astronomers have discovered that super-Earths are among the most common types of planets in our Milky Way galaxy.
In that respect, our own solar system is an oddity since it contains no super-Earths. The physical nature of exoplanets like GJ 1214b is, therefore, largely unknown since there are no near-Earth planetary bodies with which to compare them.
GJ 1214b was discovered in 2009 by the MEarth Project, a US National Science Foundation-funded robotic observatory, part of the Fred Lawrence Whipple Observatory on Mt. Hopkins, Ariz. MEarth monitors the brightness of thousands of red dwarf stars aiming to discover transiting exoplanets. After discovery, GJ 1214b was logged for follow-up observations to characterize its atmosphere.
At 40 light years distant, GJ 1214b might appear a long way away, but in astronomical terms, it lies in Earth’s backyard, making it one of the most easily observed super-Earths. Another factor making for ease of observation is the relatively small size of GJ 1214b’s host star.
GJ 1214b transits, or passes, in front of its parent star every 38 hours, giving scientists plenty opportunity to study the exoplanet’s atmosphere as starlight from the parent star filters through it.
Until the team of astronomers, led by University of Chicago’s Laura Kreidberg and Jacob Bean, detected clear evidence of clouds in the atmosphere of GJ 1214b, previous studies of the exoplanet had given rise to two possible interpretations of its atmosphere.
In 2010, the first spectral analysis of data from GJ 1214b carried out by Bean and obtained using a ground-based telescope suggested the planet’s atmosphere consisted predominantly of water vapor or that it was made up principally of hydrogen with high-altitude clouds.
Then, during 2012 and 2013, the researchers used Hubble to more precisely measure the spectrum of GJ 1214b in near-infrared light. These more detailed calibrations meant the research team were able to distinguish between the two scenarios postulated for the composition of GJ 1214b’s atmosphere.
But, rather like Sherlock Holmes, for the research team it was a case of eliminating the impossible. Spectra obtained via Hubble revealed no chemical fingerprints whatsoever in the planet's atmosphere. This meant the astronomers could eliminate cloud-free atmospheres consisting of water vapor, methane, nitrogen, carbon monoxide, or carbon dioxide.
From their observations, the research team concluded that the best explanation of GJ 1214b’s atmosphere was that there was definitive evidence of high clouds swaddling the planet. Because of the cloak of cloud cover, information about the composition and behavior of the lower atmosphere and surface remained hidden.
Computer-generated models of super-Earths such as GJ 1214b have suggested clouds could be made out of potassium chloride or zinc sulfide at the scorching temperatures of over 230 degrees Celsius found on GJ 1214b.
Deciphering what, exactly, makes up the atmosphere of this cloudy exoplanet will have to wait until the next generation of space telescopes become operational. So far, having eliminated the impossible, the favored explanation for the new data on GJ 1214b is that there exist high-altitude clouds in its atmosphere, though their composition is unknown. But as Kreidberg, a third-year graduate student and first author of the new paper, put it, "You would expect very different kinds of clouds to form than you would expect, say, on Earth.”
Kreidberg added that the team had pushed the limits of what is possible with Hubble to make their measurements but, looking ahead, the researchers’ methodology lays the foundation for characterizing other exoplanets using similar techniques.
As new space telescopes come on-stream, they hold out the prospect of astronomers finding, before long, that Holy Grail of exoplanets — a rocky Earth-like world in the habitable zone of a solar system similar to our own.
Major advances in exoplanet research are expected later this decade when NASA’s next major space telescope, the 6.5-meter James Webb Space Telescope (JWST), becomes operational. The JWST is scheduled for launch in 2018 and its capabilities will enable astronomers to peer through the murkiness of the clouds on planets such as GJ 1214b.
Kreidberg described the effect of JWST as being “transformative.” Once operational, the James Webb Space Telescope will be able to detect celestial objects that are 10 billion times as faint as the faintest stars visible to the naked eye — 10 to 100 times fainter than can currently be observed using Hubble.
Add to that the haul of exoplanets expected to be detected by the Transiting Exoplanet Survey Satellite (TESS), an MIT-backed new Earth-orbit space telescope, part of NASA's Explorer program, scheduled for launch in 2017.
Before the decade is out, astronomers are likely to be knee deep in exoplanets and seeing what no one — at least no one from Earth — has seen before, entirely unaided by warp drive.
The full research paper on exoplanet GJ 1214b, entitled, "Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b," is published in the Jan. 2 edition of the journal Nature.
More about exoplanet GJ 1214b, GJ 1214b, Hubble, Hubble space telescope
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