Astronomers detect helium atmosphere on rocky exoplanet in habitable zone

Astronomers have detected an atmosphere around a rocky planet orbiting in the habitable zone of a nearby star. The planet, LHS 1140b, is about 5.6 times as massive as Earth and 1.73 times Earth's size. Its surface temperature could support liquid water.

The host star is a cool, dim M dwarf. These stars emit harsh radiation and stellar flares that can strip planetary atmospheres. Previous studies had found helium escaping from larger planets called mini-Neptunes.

Observation method Researchers used the Magellan Clay telescope at the Las Campanas Observatory in New Mexico. They observed the planet passing in front of the star and blocking some of its light. Just before and after the transit, they recorded the molecular fingerprint of excess helium gas.

The excess helium indicates the gas is streaming away from the planet, confirming the presence of an atmosphere. The planet has already retained its atmosphere for more than 3 billion years.

Future observations Follow-up observations with the James Webb Space Telescope are planned to measure how much helium the atmosphere contains and identify other molecules. A second detection would further confirm the atmosphere's existence. The planet is losing helium at a lower rate than mini-Neptunes.

It could remain stable for another billion years and may retain heavier gases such as carbon dioxide or nitrogen.