TRAPPIST-1b and c, the two innermost planets in the three-planet system TRAPPIST-1, are primarily rocky, unlike gas giants such as Jupiter, according to a group of astronomers led by MIT scientist Julien de Wit. This artist’s impression shows an imagined view from the surface one of the three exoplanets orbiting the ultracool dwarf star TRAPPIST-1. These alien worlds – named TRAPPIST-1b, c and d – have sizes and temperatures similar...