Brice-Olivier Demory

Two new planets are circling dim red stars. One is nearly the size of Earth, the other is three and a half times larger. Both lie in what astronomers call the warm zone: a region where starlight doesn't scorch the surface but also doesn't leave it in perpetual cold. The host stars are red dwarfs, the most common stars in the galaxy.

Astronomers caught the young planet AU Mic b in the act of hiding behind its star. The Spitzer telescope tracked its infrared glow: as the planet slipped behind, the system's total light dimmed slightly. The dip was just 171 parts per million, like a single drop of ink in ten buckets of water.