Ultracool dwarf stars are widespread in the solar neighborhood. Nevertheless, their extremely low brightness has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has been found to host a transiting planetary system, until now. Astronomers with the SPECULOOS (Search for Planets EClipsing ULtra-cOOl Stars) project have now detected an Earth-sized planet in a 17-hour orbit around the nearby ultracool dwarf star SPECULOOS-3. An...