Correct Answer: A
Explanation:
The Earth-sized planets orbiting the ultracool TRAPPIST-1 dwarf star 40 light-years away may have substantial amounts of water and could be habitable.
An international team of astronomers used the NASA/ESA Hubble Space Telescope to estimate whether there might be water on the seven planets orbiting in the nearby TRAPPIST-1 planetary.
The results suggest that the outer planets of the system might still harbour substantial amounts of water.
This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable.
This makes TRAPPIST-1 the planetary system with the largest number of Earth-sized planets discovered so far.
Following up on the discovery, scientists used the Space Telescope Imaging Spectrograph (STIS) on the Hubble telescope to study the amount of ultraviolet radiation received by the individual planets of the system.
While lower-energy ultraviolet radiation breaks up water molecules - a process called photodissociation - ultraviolet rays with more energy (XUV radiation) and X-rays heat the upper atmosphere of a planet, which allows the products of photodissociation, hydrogen and oxygen, to escape.
As it is very light, hydrogen gas can escape the exoplanets’ atmospheres and be detected around the exoplanets with Hubble, acting as a possible indicator of atmospheric water vapour.
The observed amount of ultraviolet radiation emitted by TRAPPIST-1 suggests that the planets could have lost gigantic amounts of water over the course of their history.