GJ 3378b orbits a star 25 light-years from the solar system and is roughly twice Earth's size, making it one of the nearest newly identified potentially habitable exoplanets.
The planet lies in its star's habitable zone and receives about 90% of the radiation Earth gets from the sun, placing it in a range where liquid water could exist.
Researchers said its atmosphere remains the key unknown because the planet sits near the "cosmic shoreline," where stellar radiation can strip atmospheres away.
UC Irvine's team found the planet using the Habitable-zone Planet Finder in Texas and the NEID spectrometer in Arizona, with the study published in The Astrophysical Journal.
NASA's planned Habitable Worlds Observatory, targeted for the 2040s, could determine whether GJ 3378b has an atmosphere and whether it merits a search for biosignatures.