"However, some of our conclusions about the habitability of Trappist-1's seven are somewhat dampened by our fuzzy knowledge about the masses of the planets". The ultraviolet radiation emissions being observed suggest that the planets have lost huge amounts of water of the course of their history, especially two of the innermost planets TRAPPIST-1b and TRAPPIST-1c.
There could be water on multiple Earth-sized planets orbiting the recently discovered TRAPPIST-1 dwarf star - making them potentially habitable - according to an global collaboration of researchers, including the University of Warwick. We still aren't sure what kind of atmosphere - if any - surrounds the distant worlds, and it's unclear if red dwarf stars like TRAPPIST-1 are conducive to hosting habitable planets.
They are likely all tidally locked, meaning the same face of the planet is always pointed at the star, as the same side of the Moon is always pointed at Earth. As at that time, in Transiting Planets and Planetesimals Small Telescope - TRAPPIST - project scientists confirmed to have only three planets.
The team wrote in their paper that observing the TRAPPIST-1 planets over a broad wavelength range from the ultraviolet to the infrared would provide insights into the current state and the dominant physical processes shaping these planets' atmospheres.
The researchers measured the ultraviolet (UV) irradiation that the planets receive from TRAPPIST-1, as these UV rays cause water molecules to break apart into their constituent hydrogen and oxygen atoms - making them vulnerable to being driven off into space by the X-ray radiation from the star. At that stage astronomers believed that the star, 40 lightyears from Earth, had only three planets.
"The inner planets could have lost more than 20 Earth-oceans-worth of water during the last eight billion years", the scientists explain. What's more, planets e, f, and g should be able to support liquid water at their surfaces given their location within the system's habitable zone.
"Our results indicate that atmospheric escape may play an important role in the evolution of these planets", said co-author Dr. Julien de Wit, of MIT.
"We can say the inner ones probably lost a huge amount of water, and the outer ones way less, allowing them to actually still have some water, if they captured it when they first formed". "We are still a long way to determining the habitability of these planets, but our results suggest that the outer ones might be the best targets to focus our future observations".