A new study claims that two exoplanets of the TRAPPIST-1 star system might be habitable in nature. Since its discovery, the TRAPPIST-1 has captivated the scientists owing to its ultra cool atmosphere and temperate terrestrial Earth-sized planets. Previous research suggested that three of the exoplanets surrounding the TRAPPIST-1 system are orbiting in the habitable zone. Now, the latest study, carried out by PSI (Planetary Science Institute) Senior Scientist Amy Barr and his colleagues, says that two of the exoplanets in the TRAPPIST-1 star system are most likely to be habitable.
Barr said, “Because the TRAPPIST-1 star is very old and dim, the surfaces of the planets have relatively cool temperatures by planetary standards, ranging from 400 degrees Kelvin (260 degrees Fahrenheit), which is cooler than Venus, to 167 degrees Kelvin (-159 degrees Fahrenheit), which is colder than Earth’s poles. That is why the TRAPPIST-1 is called as the ultra-cool red dwarf star instead of a brown dwarf. Barr further informed that the planets also orbit very close to the TRAPPIST-1 star and their orbital periods are of a few days only. Instead of circular, the orbits of the planets are eccentric there is chance that they could experience tidal heating just like the moons of Saturn and Jupiter, as said by Barr.
As it is known that the exoplanets orbiting in the habitable zone of its parent star system might possess liquid water on its surface, same can be thought of the two exoplanets of the TRAPPIST-1 system. According to Barr, assuming the planets to be composed of water ice, rock and iron, one can determine how much of each might be there inside the planet and how thick the different layers would be. Barr got to know that the masses and radii of the planets are not very well-constrained and that is why they showed the full range of the possible interior structures and their compositions. The study suggests that if the estimates of masses of the planets become more accurate and precise then, there is a greater chance of knowing whether the planets carry a significant amount of water or not.
The analysis made by co-author Vera Dobos revealed that out of the seven planets orbiting the TRAPPIST-1 system, two planets named d and e are most likely to be habitable owing to their moderate surface temperatures as well as modest amounts of tidal heating. Also, the heat fluxes of both the planets are low enough to avoid entering a runaway greenhouse state. According to the study, there is a chance that a global water ocean might be present on the planet d.