We’re going to eventually get to know the seven planets of the TRAPPIST-1 system well. That’s because they present the ideal targets for upcoming attempts to probe the atmospheres of Earth-sized rocky planets.
Some of the exoplanets surrounding the nearby dwarf star may contain liquid water on their surface, according to observations made with the Hubble Space Telescope.
If true, this would be a major breakthrough for investigations into whether or not the exoplanets could host life as we know it.
It is the planetary system with the largest number of Earth-sized planets discovered so far.
Scientists say it's possible five Earth-sized planets orbiting Trappist-1 and announced in February 2017. TRAPPIST-1 is an ultra-cool dwarf star located 39 light years away, contain "significant amounts of water." An international team of astronomers used the Hubble Space Telescope (HST) to measure the amount of ultraviolet (UV) radiation hitting all seven TRAPPIST-1 exoplanets. The phenomenon is important because low-energy UV radiation can break down water molecules into hydrogen and oxygen; higher levels heat the upper atmosphere to the point where the two elements can escape. UV radiation is therefore useful in modelling water loss and atmospheric stability in distant planets.
Following this revelation, a team of astronomers began using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope to study the amount of ultraviolet radiation from the host star that hits each of the planets.
“Ultraviolet radiation is an important factor in the atmospheric evolution of planets,” says Vincent Bourrier from the Observatoire de l’Université de Genève, who led the study.
“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.”
Hydrogen gas created on the exoplanets through this process is very light and can escape the atmosphere and be detected by the Hubble Space Telescope.
This means that the detection of hydrogen could be a sign of water on the surface of the planets.
Observations of the amount of ultraviolet radiation emitted by the TRAPPIST-1 star suggests the planets could have lost a lot of water over the course of their history.
The innermost two planets of the system, TRAPPIST-1b and TRAPPIST-1c, receive the largest amount of ultraviolet energy. They could have lost an amount of water equivalent to 20 times that of Earth’s oceans over the last billion years, according to the study.
While that sounds pretty bad, other possibilities exist. The team says the four planets furthest from the star, E, F, G and H, "might have lost less than three Earth oceans." B and C, the two closet to Trappist-1, are the least likely to hold water, unsurprisingly.
Planets E, F and G sit in the "habitable zone," an orbital distance that could, in theory, allow Earth-like planets to hold liquid water on their surface and, by extension, support life. It's here, of course, that scientists are most hopeful about the Trappist-1 system.
Furthermore, depending on photolysis, which is the separation of molecules by light, it's possible all of the planets apart from B and C harbor water above ground. "Naturally, this also depends on the age of the system," the team of astronomers explain in their report, and how much water the planets originally formed with.
The outer planets of the system, however, are already known to orbit the star in the 'habitable zone'. These exoplanets, named e, f and g, probably have lost much less water than the inner planets, and could potentially have retained some on their surface. In theory, this could make them potentially habitable.