The new analysis claims that the TRAPPIST-1 planets in the habitable zone do not look like the solid worlds of the solar system, as they are composed mainly of water and are covered by the global ocean.
Astronomers from the PRC and the United States used data from the Kepler space telescope to refine the composition of the recently discovered planets of the TRAPPIST-1 system. It turned out that those of them that are in the zone of potential habitability are far from Earth, Venus or Mars in their composition. Most likely, they have a lot more water and are covered by a deep ocean. On the sides of these planets facing the luminary, the ocean is most likely liquid, and on the night side it is covered with ice. Terminators may have areas suitable for cold-loving land life. The corresponding article is being prepared for publication in The Astrophysical Journal, and its preprint can be found on the Cornell University website.
The authors of the work used the results of 73.6 days of observations of the disk of the TRAPPIST-1 star by the Kepler space telescope and compared them with previously obtained data from other telescopes. According to revised estimates, the masses and densities of the planets of the system differ significantly from those previously identified by European astronomers. TRAPPIST-1e showed 0.24 Earth mass (early estimate 0.62), TRAPPIST-1f 0.36 Earth mass (was 0.68), and TRAPPIST-1g 0.57 (was 1.34).
This dramatically changes the idea of their density. If earlier it was considered close to Venusian, Martian or terrestrial, now it turned out to be much smaller, close to the large moons of Jupiter and Saturn - in the range from 1.34 to 2.18 grams per cubic centimeter, which is 2.5-4 times less than the Earth. At the same time, this density speaks against the previously popular version that the stellar wind and hard radiation from the local red dwarf could deprive the local planets of light gases and water. If so, their density would be much higher.
Such a low density is typical for bodies in which up to half of the mass is water. The three planets mentioned receive from their star an amount of radiation similar to that which falls on the earth's surface. Therefore, the illuminated side of these planets (they are close to the star, and one side is constantly looking at it) must be covered by a liquid ocean, at least in part.
The question of the habitability of the oceanid worlds is not yet completely clear, since in the solar system all bodies with a global ocean (perhaps such is Europe, a satellite of Jupiter) are hidden by ice, which makes them difficult to study. Nevertheless, it is known that the oceans there cannot be deeper than 200 kilometers, because after this mark the pressure becomes too great for the existence of liquid water and it becomes exotic hot, but solid ice. If these three planets are turned to the luminary by one side, then on the terminator there is a boundary of ice, where theoretically the existence of some kind of life is possible.