Kepler Data Reveals Earth-Size Exoplanet on the Edge of Its Star’s Habitable Zone

Scientists analyzing old data from NASA's Kepler Space Telescope have discovered an Earth-size exoplanet candidate that looks similar to our own planet, but could be much colder. The planet, named HD 137010 b, is a rocky world that is just slightly larger than Earth and circles a sun-like star located about 146 light years from us. Its orbit could be just a year long, so it is on the outer edge of this star's habitable zone. But early estimates hint that the planet could even be colder than Mars, leaving open the question of whether it is capable of hosting life-friendly conditions.

Kepler Data Suggests Planet Receives Far Less Heat Than Earth

According to a report published in The Astrophysical Journal Letters, the planet was detected during the K2 mission of Kepler from a single transit event, in which the planet transitted for a short time in front of its host star. The star is cooler and dimmer than the Sun, so that the planet gets less than a third of the light and heat our Earth receives.

This limited energy could leave surface temperatures near minus 90 degrees Fahrenheit, colder than Mars on average. Even so, scientists note that temperature estimates depend heavily on the planet's atmosphere, which remains unknown. A thick, carbon dioxide–rich atmosphere could trap heat and soften these harsh conditions.

Rare Orbit Makes Planet Hard to Confirm, but Scientists Remain Hopeful

That planet's still a candidate after only one observed transit, though, since earthlike orbits are difficult to pin down. NASA's TESS mission or Europe's CHEOPS satellite may eventually be able to confirm that.
Researchers say the planet may lie in a wider habitable zone and remains one of the most promising cold Earth-sized candidates, despite possibly being frozen.