Artist's impression of the TRAPPIST-1 planetary system.
Fortunately, there's still some hope for the outer planets in the system. In this view, the planets in the sky correspond to TRAPPIST1e (top left crescent), d (middle crescent) and c (bright dot to the lower right of the crescents). However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped once they entered the habitable zone. Image credit: NASA / JPL-Catlech.
Since its discovery in 2016, the ultracool dwarf TRAPPIST-1planet, located 39 light years away has been an intriguing topic for astronomers. It is barely larger than Jupiter and has just 8% of our Sun's mass.
One study said solar flares from the host star would cause massive geomagnetic storms on the planets and life as we know it could not survive, while another hinted at possible vegetation on at least one world.
They are likely all tidally locked, meaning the same face of the planet is always pointed at the star, as the same side of the Moon is always pointed at Earth.
Water could be present on some of the Earth-sized planets orbiting the dwarf star TRAPPIST-1, according to work from an global group of astronomers.
The level of ultraviolet energy projected onto each planet is important. "As in our own atmosphere, where ultraviolet sunlight breaks molecules apart, ultraviolet starlight can break water vapor in the atmospheres of exoplanets into hydrogen and oxygen".
During the research period, they studied the quantity of inward ultraviolet or UV radiation, received by each of the seven planets of the TRAPPIST-1 system, and conducted a series of calculations for determining how this emission might be dominating the amount of water on each planet. Calculations made by Bourrier's team suggests that the two innermost planets, TRAPPIST-1b and TRAPPIST1-c, have lost very big loads of water over the course of their history.
This is especially true for the innermost two planets of the system, TRAPPIST-1b and TRAPPIST-1c, which receive the largest amount of UV energy.
It shows that "atmospheric escape may play an important role in the evolution of these planets", said Julien de Wit, co-author of the study and a researcher from the Massachusetts Institute of Technology.
The amount of ultraviolet radiation emitted by TRAPPIST-1, does indeed suggest that the planets could have lost enormous amounts of water - more than 20 Earth-oceans-worth of water for the inner two planets alone during the last eight billion years. Their results suggest that the outer planets of the system - including the three worlds in the habitable zone - might be capable of harboring substantial amounts of water.
The astronomers sought to predict how much water each planet may have lost over its history.
"It depends a lot on their initial water content", Dr. Bourrier added.
They likely represent upper limits on the actual water loss because our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres should be the limiting process. From all the studies done on this system, astronomers think the seven planets may have originally formed much farther out from their star, in a cold region that contains crystals of water ice.