Free Astronomy Magazine July-August 2016

TRAPPIST-1b and TRAPPIST-1c respectively receive from their star four times and twice as much energy as the Earth receives from the Sun, and it is thus likely that their atmo- spheres are a little too hot (but not as hot as that of Venus). Because of their prox- imity to TRAPPIST-1, it is assumed that two planets' periods of rotation and revolution are synchronized and thus presenting al- ways the same hemisphere to their star, while the other remains in perpetual dark- ness. According to Gillon’s team this could cause temperatures to vary within a range of +130 degrees C and -30 degrees C. Accordingly, along the terminator there may be a more or less wide band in which conditions would, on the whole, be live- able. To this would also contribute the ther- mal stability of the star, which, in having been formed about 500 million years ago, will remain in its current state for further tens of billions of years. The most interesting target remains, how- ever, TRAPPIST-1d, which due to its greater distance from the star has not yet under- gone the synchronization of the rotational and orbital periods, which in the specific case will be achieved, according to Gillon and colleagues, in about half a billion years. to have gaseous envelopes not dominat- ed by hydrogen and helium, and thus more similar to the atmospheres of Venus and Earth than to that of a mini-Neptune. A bove, the ro- botic TRAP- PIST telescope. This instrument is remotely control- led by the Univer- sité de Liège, Bel- gium. [E. Jehin/ESO] Right, an imagi- nary view of TRAPPIST-1d, the first planet on which evidence of extraterrestrial life may be found. [ESO/M. Kornmes- ser/N. Risinger]