Nearly a decade after the discovery of LHS 1140b—a rocky exoplanet orbiting in the habitable zone of a nearby red dwarf—new results suggest the world may still be shrouded in an atmosphere. The finding reframes a key expectation in exoplanet science: that small, mature rocky planets around dwarf stars usually lose their air over time.
Researchers led by University of Florida Assistant Professor of Astronomy Jason Dittmann used helium escape to probe the planet’s upper atmosphere. Their study, published in Science, reports evidence that helium is leaving the planet at a rate too high to be explained by a dwindling “leftover” helium reservoir alone.
The signal was captured with the Magellan Clay telescope at Las Campanas Observatory in Chile. To interpret why helium should be present despite the planet’s age, the team combined helium measurements with stellar energy conditions—specifically X-ray data that quantify how strongly the host star irradiates the planet.
That X-ray input matters because high-energy photons heat the upper atmosphere and can drive atmospheric particles upward until they escape. By linking the observed helium loss to the star’s X-ray luminosity, the authors infer that LHS 1140b must be replenishing helium continuously. Without such replenishment, helium would have largely vanished long ago.
This inference echoes atmospheric escape seen on Earth, but under markedly different stellar forcing. It also offers an important bridge between two ideas: that rocky planets can be largely airless, and that some may retain atmospheric components in a “steady-state” exchange with ongoing escape.
Dittmann originally discovered LHS 1140b in 2016 using ground-based transit searches. Because Earth’s own atmosphere can mimic or distort subtle dimming signals, he applied a machine-learning approach to distinguish planetary transits from terrestrial weather effects.
With JWST and Hubble’s ongoing “Rocky Worlds” observing efforts, the next steps focus on detecting molecules beyond helium. If signatures such as water vapor—or related carbon dioxide—emerge, it would strengthen the case for a stable atmosphere rather than an intermittent gas “burp” that rapidly evaporates.
The team expects that within roughly four to five years, observations will either confirm atmospheric persistence or push the planet toward a bare-rock interpretation. In either outcome, LHS 1140b is poised to become a flagship test case for how atmospheres survive around dwarf stars—and for whether the most Earth-like candidates truly stay habitable.
Keywords
Helium escape; LHS 1140b; rocky exoplanets; dwarf stars; habitable zone; atmospheric loss; X-ray irradiation; JWST; Hubble; machine learning
