Hubble data indicates TRAPPIST-1 planets may have water

Low-energy ultraviolet radiation breaks water up molecules into hydrogen and oxygen through a process known as photo-dissociation.
By Laurel Kornfeld | Sep 05, 2017
Five of the seven Earth-sized planets orbiting the red dwarf star TRAPPIST-1 may still have significant amounts of water, according to observations of the system conducted by an international team of astronomers using the Hubble Space Telescope.

The outermost planets in the system, including TRAPPIST e, f, and g, which are located in the star's habitable zone, may still retain enough water to be habitable.

Led by Swiss astronomer Vincent Bourrier of the Observatoire de l'Universite de Geneve, the scientists used Hubble's Space Telescope Imaging Spectrograph (STIS) to measure the amount of ultraviolet radiation each planet in the system receives from the star.

Low-energy ultraviolet radiation breaks water up molecules into hydrogen and oxygen through a process known as photo-dissociation.

High-energy ultraviolet radiation, along with X-rays, heat planets' atmospheres, enabling elements produced by photo-dissociation to escape into space.

Being closest to the star, TRAPPIST 1b and c receive the highest levels of ultraviolet radiation, which could have caused them to lose as much as 20 Earth oceans of water over eight billion years.

"Ultraviolet radiation is an important factor in the atmospheric evolution of planets," Bourrier explained. "As in our own atmosphere, where ultraviolet sunlight breaks molecules apart, ultraviolet starlight can break water vapor in the atmospheres of exoplanets into hydrogen and oxygen."

However, the three planets in the habitable zone may have retained enough water on their surfaces to stay habitable.

Calculations of water loss rates for the system's two outermost planets suggest these too may have held onto sufficient water to support life.

The scientists recommend using the James Webb Space Telescope (JWST), scheduled for launch in 2018, to continue the search for water on the TRAPPIST-1 worlds, as well as followup observations of them in all wavelengths of light.

Results of the study will be published in the journal Earth and Planetary Astrophysics.

 

 

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