The concept, known as "superhabitable worlds," describes theoretical planets roughly 20 to 30 percent wider than Earth and about twice as massive, orbiting cooler, longer-lived stars called K-dwarfs. Astronomers René Heller and John Armstrong first laid out the idea in a 2014 paper, arguing that Earth's run as a home for complex life is capped at around 500 million years because the Sun keeps getting brighter. A planet circling a K-dwarf star instead of a sun like ours could avoid that constraint, since K-dwarfs burn cooler and last much longer.

Heller and Armstrong theorized that such planets could also have thicker atmospheres, stronger magnetic fields and vast shallow seas, features that together could support greater biodiversity over a far longer stretch of time than Earth has available.

Iva Vilovic, a researcher at the Leibniz Institute for Astrophysics in Germany, tested part of that theory in a Berlin laboratory by growing garden cress under artificial light tuned to mimic a K-dwarf star. The cress grew faster and taller than under Sun-like light, a result Vilovic's experiment suggests points to photosynthesis working more efficiently under K-dwarf starlight.

No superhabitable planet has been confirmed to exist. The European Space Agency's PLATO mission, set to launch in 2027, is designed to search for candidates. NASA's Habitable Worlds Observatory, expected in the 2040s, would follow up by analyzing the atmospheres of any candidates for signs of biological activity.