By Cheyenne Macdonald
Four planets orbiting the dwarf star at the heart of the Trappist-1 system, including three in the habitable zone, may contain substantial amounts of water.
This is according to a new study based on observations by the Hubble Space Telescope, which has allowed researchers to assess the amount of ultraviolet radiation each planet in the nearby star system is subjected to.
While the inner planets likely lost massive quantities of water over billions of years, with the equivalent of over 20 Earth oceans thought to have escaped, those in the outer reaches may have avoided the worst of these effects, boosting hopes for their habitability, according to Daily Mail.
Of the seven planets in the Trappist-1 system, three are located in the habitable zone, where it's thought the conditions would be right to sustain liquid water at the surface.
The new findings from an international team of astronomers offer the first hints that this may be the case.
"Ultraviolet radiation is an important factor in the atmospheric evolution of planets," said lead author Swiss astronomer Vincent Bourrier, from the Observatoire de l'Universite de Geneve.
"As in our own atmosphere, where ultraviolet sunlight breaks molecules apart, ultraviolet starlight can break water vapour in the atmospheres of exoplanets into hydrogen and oxygen."
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.
This escaping hydrogen gas can then be detected around the exoplanet, using instruments like the Hubble Space Telescope.
In observing Trappist-1, and calculating the water loss rates and the geophysical water release rates, the researchers found that some of the planets may have lost huge amounts of water as a result of the incoming ultraviolet radiation from their host star.
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 eight billion years, according to the study.
But Trappist-1e through h may have lost far less water.
If the process, known as hydrodynamic escape, stopped once the planets entered the habitable zone, it's possible they lost the equivalent of less than three Earth oceans.
"Our results indicate that atmospheric escape may play an important role in the evolution of these planets," said co-author Julien de Wit, of MIT.
Still, they say no final conclusion can be drawn yet, due to the limited nature of the data and telescopes.
According to Bourrier, these three planets could be key targets for the upcoming James Webb Space Telescope, as well as further theoretical studies.
"Hubble's observations are of great significance, since they inform us on the irradiative environment of the Trappist-1 planets, notably on whether they can remain habitable for billions of years, like Earth has," said Dr Amaury Triaud, from the School of Physics and Astronomy at the University of Birmingham.
"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.
"Crucial observations, able to refine the planetary masses, are being obtained as we write."