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Published: Sat, September 02, 2017
Research | By Jennifer Evans

Hubble Suggests Outer TRAPPIST-1 Planets May Have Substantial Water

Hubble Suggests Outer TRAPPIST-1 Planets May Have Substantial Water

There is still so much to learn out about the TRAPPIST-1 system, the set of planets orbiting a (relatively) nearby ultracool dwarf star that so excited the exoplanet community earlier this year. Scientists believe that for life as we know it to exist outside our own planet, surface water must be present. Now in a recent breakthrough, a team of scientists has discovered the possible presence of water in three habitable planets of the star system.

Lower-energy ultraviolet radiation is known to break up water molecules - and, combined with higher-energy UV and X-rays, a planet's upper atmosphere can heat up enough to allow these breakdown products to escape.

Using the NASA/ESA Hubble telescope to estimate whether there might be water on the surface of the seven planets around TRAPPIST-1, the researchers found that although the innermost planets must have lost most - if not all - of their water, the outer planets of the system might still harbour substantial amounts.

Artist's impression of the TRAPPIST-1 planetary system.

Vincent Bourrier at the University of Geneva in Switzerland and his colleagues tracked the UV radiation that reaches TRAPPIST-1's planets.

The hydrogen and oxygen gas molecules leaving the planet's atmosphere can be detected as a water vapor.

A paper published Thursday in The Astrophysical Journal describes the results gathered from the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. They also looked for any hydrogen "escaping" from the atmospheres, since that detection would be an indication of water vapor.

The new study looks at how much ultraviolet (UV) radiation is received by each of the planets, because this could affect how much water the worlds could sustain over billions of years, according to the study.

"It is very likely that the planets formed much farther away from the star [than they are now] and migrated inwards during the first 10 million years of the system", Gillon told Space.com in an email.

TRAPPIST-1 may be small and dim, but dwarf stars like it often emit powerful flares of radiation that could make water and life on its planets impossible without thick protective atmospheres. "Our results indicate that atmospheric escape may play an important role in the evolution of these planets", summarises Julien de Wit, from MIT, USA, co-author of the study.

"While our results suggest that the outer planets are the best candidates to search for water with the upcoming James Webb Space Telescope, they also highlight the need for theoretical studies and complementary observations at all wavelengths to determine the nature of the TRAPPIST-1 planets and their potential habitability", he said.

As the study paper claimed, it is possible that the six innermost planets of the TRAPPIST-1system, coated with the maximum levels of ultraviolet radiation, could have lost almost worth of 20 Earth's Ocean water some 8 billion years ago.

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