SUBSTANTIAL WATER MAY EXIST ON TRAPPIST-1 PLANETS

 An international team of astronomers using the NASA/ESA Hubble Space Telescope have concluded that the outer planets of the nearby TRAPIIST-1 star system might still harbour substantial amounts of water. This would include the three planets within the habitable zone of the star, providing more evidence to the possibility of their habitability.
 To reach this conclusion, the team led by Swiss astronomers Vincent Bourrier of the Observatoire de l’Université de Genève utilized Hubble's Space Telescope Imaging Spectrograph (STIS) to determine the amount of ultraviolet radiation that each planet likely receives in the system.
 Ultraviolet radiation plays a big role in the atmospheric evolution of a planet. Lower-energy UV radiation is capable of breaking up water molecules through a process called photodissociation while higher-energy UV rays and X-rays can heat the upper atmosphere of a planet, allowing the products of photodissociation, hydrogen and oxygen, to escape.
 This hydrogen that escapes can be detected and measured around exoplanets by Hubble. The amount of UV radiation observed to have been emitted by TRAPPIST-1 suggests that while the inner planets may have lost over 20 Earth-oceans-worth of water during the last eight billion years, the outer planets have probably lost a lot less water. This could make them prime candidates for the upcoming James Webb Space Telescope to investigate.
Read more about this fascinating story at: http://earthsky.org/space/first-hints-of-water-on-trappist-1-planets