Hebrew University astrophysicist argues the 'habitable zone' is far wider than thought

For decades, the search for life beyond Earth has been guided by the idea of a 'habitable zone': the ring of orbits around a star where a planet receives just enough warmth to keep liquid water on its surface. In a paper published in The Astrophysical Journal on 12 January 2026, and publicised by the Hebrew University on 26 January, astrophysicist Amri Wandel of the university's Racah Institute of Physics argues that this conventional zone is drawn far too narrowly.

Wandel focused on tidally locked planets, which always present the same face to their star, as the Moon does to Earth. Such planets are expected to be common around M and K dwarfs, the small, cool stars that make up most of the galaxy. Using an analytical climate model, he showed that heat carried from the scorching day side can keep the permanently dark night side mild enough for liquid water, even on planets orbiting much closer to their star than the standard inner boundary allows. He calculated new, extended boundaries for where water could survive.

The study also looks outward. Beyond the cold outer edge of the usual habitable zone, he notes, water could persist as lakes beneath or within thick ice sheets, much as subglacial lakes exist under Antarctica. Taken together, these effects could increase the number of potentially water-bearing worlds by a large factor.

The work may help make sense of recent observations by the James Webb Space Telescope, which has detected water vapour and other volatile gases around warm, Earth-sized and super-Earth planets orbiting close to M dwarfs, places that the classical habitable-zone map would have dismissed as too hot.