A Most Promising Super-Earth
Meet LHS 1140 b, a planet that has been on astronomers' shortlists for years. Discovered in 2017, it's what scientists call a 'super-Earth'—a rocky world significantly larger and more massive than our own, specifically about 1.7 times our radius and 5.6
times our mass. It orbits a cool, dim red dwarf star right in the middle of the habitable zone, the region where temperatures could theoretically allow for liquid water on the surface. Located just 49 light-years away in the constellation Cetus, it's a prime candidate for a world that could potentially harbour life. But a key question has always lingered: does it have an atmosphere? Without a protective gaseous blanket, a planet's surface is exposed to harsh stellar radiation and cannot regulate its temperature, making liquid water and life as we know it impossible. Previous studies were inconclusive, leaving its true nature a mystery.
A New Tool for a New Approach
Finding atmospheres on rocky exoplanets is incredibly difficult. The signals from gases like water or carbon dioxide in the lower atmosphere are faint and often beyond the reach of even our most powerful telescopes. So a team of astronomers decided to try a different tactic. Instead of looking for what was deep inside the atmosphere, they looked for what might be leaking out from the very top. Using a highly sensitive ground-based instrument in Chile called the WINERED spectrograph, they targeted LHS 1140 b. WINERED, an acronym for Warm INfrared Echelle spectrograph to Realize Extreme Dispersion and sensitivity, is attached to the Magellan Clay telescope and is exceptionally good at breaking down infrared light into its constituent parts, allowing scientists to identify specific chemical elements. The team pointed it at the planet, hoping to spot the signature of helium, a light gas that would be expected to populate the upper layers of a planet's atmosphere before slowly escaping into space.
The Telltale Signature of Escaping Gas
The observations delivered a stunning result. The WINERED data clearly showed a telltale signature of helium gas being stripped from LHS 1140 b and trailing behind it. While the headline might sound like bad news—a leaky balloon losing its air—the scientific implication is precisely the opposite. The fact that gas is escaping at all is the first direct, confirmed evidence that LHS 1140 b has a substantial atmosphere. For a planet to be losing helium after billions of years, it must have a large atmospheric reservoir to replenish it from below. This finding transforms the planet from a potential candidate into a confirmed atmospheric world, a landmark achievement in the hunt for habitable exoplanets. Lead author Collin Cherubim noted this is the first time an atmosphere has been confirmed on a rocky planet within another star's habitable zone.
A Dynamic and Changing Sky
The discovery came with another fascinating twist. The strong signal of escaping helium was detected in observations from 2024, but when the team looked again in 2025, the signal was gone. This suggests the atmospheric escape isn't constant but variable. The likely cause is the planet's host star. Red dwarfs are known for their volatility, and scientists believe that periodic bursts of X-ray and ultraviolet radiation from the star are heating the planet's upper atmosphere, causing the helium to puff away in intermittent bursts. Witnessing an exoplanet's atmosphere change on such a short, human timescale is a rare privilege and provides valuable insight into the dynamic interactions between stars and their planets. The observations also looked at a neighboring planet, LHS 1140 c, which showed no signs of an atmosphere, further cementing the significance of the discovery on its larger sibling.
