Astronomers Report Helium Signal from Rocky Exoplanet LHS 1140 b, Unconfirmed in Follow-Up Observation

Astronomers detected an atmosphere on the rocky exoplanet LHS 1140 b for the first time through observations that captured a spectral line from excited helium atoms. The signal appeared during a transit on a night in September 2024 at the Las Campanas Observatory in Chile using the WINERED spectrograph.

Researchers interpreted the line as helium escaping from the planet at hundreds of thousands of kilograms per second and heated above 4,700 degrees Celsius.

LHS 1140 b orbits an M-dwarf star roughly 50 light-years from Earth. The planet has more than five times Earth's mass and 1.7 times its radius, and it lies in the star's habitable zone. The host star is about one-fifth the mass and size of the Sun.

A second observation with the same instrument in 2025 found no helium signature. Separate reanalysis of both datasets confirmed the differing outcomes. "By far the most simple explanation is that this helium that we see is from the planet itself," Collin Cherubim, lead author and planetary scientist at Harvard University, said.

The study appeared in the journal Science. "This planet has now become the best place to search for life outside of our solar system," Cherubim said. A 2025 non-detection leaves the outflow's variability unexplained, though Cherubim plans further observations.