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Scientists Say Some of TRAPPIST-1 Planets Just Might Have Water
November 24 2017, 09:56 | Guillermo Bowen
Hubble provides first hints of water on nearby TRAPPIST-1 planets
Astronomer Vincent Bourrier of the Observatoire de l'Université de Genève led an worldwide team that included scientists from NASA and MIT to attempt to determine if there's water 40 light-years away on the seven Earth-sized planets orbiting TRAPPIST-1, a system which claims the biggest number of Earth-sized planets we've found to date. The finding spurred a team of scientists to investigate the possibility of water-and thus maybe life-in the system.
An global team of astronomers, led by Vincent Bourrier from the Observatoire de l'Université de Genève, used Hubble's Space Telescope Imaging Spectrograph (STIS) to look at the amount of ultraviolet radiation the planets might receive from their star, and how that might affect the planets' atmospheres. In the atmospheres of exoplanets, lower-energy UV radiation can break molecules of water vapor into hydrogen and oxygen.
Three out of the seven planets are in the habitable zone, the magical region where liquid water can theoretically exist.
"Ultraviolet radiation is an important factor in the atmospheric evolution of planets", Vincent Bourrier, one of the scientists who made this discovery, said in a statement.
Part of this meant examining the amount of UV radiation hitting each of the planets.
An artist's concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets' diameters, masses and distances from the host star.
A paperpublished Thursday in The Astrophysical Journal describes the results gathered from the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. But at higher doses, extreme UV and X-rays heating the upper atmosphere of a planet pass on enough energy for the hydrogen and oxygen, which have been broken up by photodissociation, to escape.
"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. "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.
The inner planets, Trappist-1b and d may be in a runaway phase, and Trappist-1g may have lost over 20 Earth oceans worth of water over the course of 8 billion years, according to the study. "However, the outer planets of the system - including the planets e, f and g which are in the habitable zone - should have lost much less water, suggesting that they could have retained some on their surfaces".
Using the STIS, the researchers could detect any escaped hydrogen gas around the atmosphere of each planet, which helped them determine the likelihood of atmospheric water vapor.