Free Astronomy Magazine March-April 2018

EXOPLANETS 5 F rom time to time it is unavoidable to go back to talking about TRAPPIST-1, a decid- edly dwarf and relatively cold star, around which there are as many as seven planets of a size comparable to that of Earth’s. We had al- ready talked about this system a couple of years ago (2016; 4), on the occasion of the discovery TRAPPIST-1 T his artist’s impression compares the seven planets orbiting the ultra-cool red dwarf star TRAPPIST-1 to the Earth at the same scale. New observations, when combined with very sophisticated analysis, have now yielded good estimates of the densities of all seven of the Earth-sized planets and suggest that they are rich in volatile materials, probably water. They are shown to the same scale but not in the correct relative positions. [ESO/M. Kornmesser] MARCH-APRIL 2018