Two of the seven exoplanets in the TRAPPIST-1 system studied by the team are most likely to be habitable, says a paper published by a researcher at the Arizona-based Planetary Science Institute (PSI).
A press release issued by the institute holds that all seven planets in TRAPPIST-1, a planetary system located 39 light years away from our solar system, are roughly the size of Earth. The planets studied are referred to by letters b through h, in order of their distance from the star. Analyses performed by the lead author, Amy Barr, and co-author, Vera Dobos, show that planets d and e are most likely to be habitable due to their moderate surface temperatures, modest amounts of tidal heating, and because their heat fluxes are low enough to avoid entering a runaway greenhouse state.
The PSI statement, available on their website, notes that all of planet d’s surface appears to be covered in water.
The surface temperature of the planets in the TRAPPIST-1 system ranges from -106 to 106 degree Celsius. Temperatures in this range are considered relatively cool by planetary standards.
The statement attributes these temperatures to the old and dim TRAPPIST-1 star that is 12 times less massive than our Sun and is slightly larger than Jupiter.
The study finds that the planets orbit very close to the star, with orbital periods of a few days. “Because their orbits are eccentric – not quite circular – these planets can experience tidal heating just like the moons of Jupiter and Saturn,” it says.
“Assuming the planets are composed of ice, rock, and iron, we determine how much of each might be present, and how thick the different layers would be. Because the masses and radii of the planets are not very well-constrained, we show the full range of possible interior structures and interior compositions,” Barr is quoted as saying in the statement.
The study holds that improved estimates of the masses of each planet can help determine the exact amount of water they hold.
The team has calculated the balance between tidal heating and heat transport by convection in the mantles of each planet. “Results show that planets b and c likely have partially molten rock mantles. Planet c likely has a solid rock surface, and can have eruptions of silicate magmas on its surface driven by tidal heating, similar to Jupiter’s moon Io,” the statement says.
The study titled Interior Structures and Tidal Heating in the TRAPPIST-1 Planets has been published in Astronomy & Astrophysics journal.