Hubble Telescope spots signs of water in alien atmospheres

Scientists conducting a detailed census of alien worlds have used the Hubble Space Telescope to analyze the water content of their atmospheres, and found the faint signature of water on five different planets.

"To actually detect the atmosphere of an exoplanet is extraordinarily difficult. But we were able to pull out a very clear signal, and it is water," L. Drake Deming, an astronomy professor at the University of Maryland who led the census teams, said in a statement.

The difficulty in looking at planet atmospheres comes from the fact that they are so far away, and so small compared to the bright star that they orbit around. However, just like the Kepler telescope, Hubble is capable of watching for planetary transits — when a distant world passes in front of its star — but Hubble can look beyond visible light. Since the atmosphere of a planet will absorb different wavelengths of light at different levels, and based on what is in the atmosphere, a study of a transit at different wavelengths can tell you how deep and thick the atmosphere is, and can tell you the atmosphere's composition.

NASA Goddard Spaceflight Center put out this great video today, describing how this is done:

The planets Demings' teams found these water signals on are WASP-17b, HD209458b, WASP-12b, WASP-19b and XO-1b. None of these planets are likely to actually have life as we know it, because they are 'hot Jupiters' — massive gas giant planets very close to their star, taking only between 18 and 94 hours to go around in their orbits. However, they make excellent planets to study, since they have deep atmospheres and they go through several transits during Hubble's viewing time, and they'll make an excellent basis for studying the atmospheres of the other planets as well.

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"We're very confident that we see a water signature for multiple planets," said Avi Mandell, a NASA Goddard planetary scientist who was the lead author of one of the journal articles published today. "This work really opens the door for comparing how much water is present in atmospheres on different kinds of exoplanets, for example hotter versus cooler ones."

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