Astronomers detected helium leaking from the atmosphere of the rocky exoplanet LHS 1140b, located within its star’s habitable zone. While a second observation failed to show the gas, the tentative finding suggests the planet may harbor a stable secondary atmosphere capable of supporting liquid water and potential life.
Exoplanet LHS 1140b and Its Faint Red Star in Cetus
Exoplanet science marked a notable shift as reports of helium gas escaping from the atmosphere of LHS 1140b moved the distant world from academic journals into wider public view. The exoplanet orbits a faint red star positioned within the constellation of Cetus, which draws its name from a whale-like sea monster in Greek mythology and sits directly beside the recognizable Cassiopeia constellation.
The host star appears roughly 10,000 times fainter than the dimmest star visible to the unaided human eye. It possesses about one-fifth the mass of our sun and shines roughly 300 times fainter, yet viewers on Earth can track a regular brightness dip every 24.7 days as the planet crosses in front of it.
Weighing a Super-Earth Against a Mini-Neptune
When the planet was discovered in 2017, researchers calculated its diameter at roughly 1.7 times that of Earth by measuring the scale of the brightness dip. Later observations, however, indicated the celestial body might span just over five times the size of our home planet, placing it firmly among the category of super-Earths.
Classifying these worlds presents a persistent hurdle for astronomers because the solar system lacks an intermediate benchmark between Earth and Uranus, which spans 14 Earth masses, followed by Neptune at 17 Earth masses. Because comparable sub-Neptunian planets appear to be the most prevalent type across the galaxy, the exact nature of LHS 1140b remains difficult to pin down due to this gap in planetary physics.
The Search for a Stable Secondary Atmosphere
The detection of leaking helium carries significant weight regarding the planet’s atmospheric history. Earlier evaluations using the James Webb Space Telescope eliminated the possibility of a primary hydrogen-rich atmosphere—a transient gaseous envelope that forms alongside newborn planets before quickly bleeding off into space.
The newly identified helium points instead toward a secondary atmosphere. These secondary layers endure over vast spans of time, influenced by internal geology, chemistry, and surface conditions. On Earth, a long-standing secondary atmosphere has persisted for billions of years, mirroring the biological and chemical balance of the planet.
Surface Temperatures and Tenuous Results
Situated inside the habitable zone of its host star, LHS 1140b draws intense interest due to the theoretical possibility of surface temperatures hovering between 0 C and 100 C, or 32 F and 212 F, which could allow liquid water to pool on the surface. Yet calculating exact thermal ranges proves complex. Under an assumption of complete stellar radiation absorption, the equilibrium temperature would rest at -30 C, or -22 F, where a thick greenhouse atmosphere could theoretically trap enough heat to warm the ground.
Alternative mathematical models suggest the planet could drop as low as -90 C, placing it closer to the harsh conditions found on modern-day Mars. Furthermore, the observational data itself remains elusive. This marks only the second instance where astronomers have detected signs of an atmosphere around a remotely Earth-like world, following similar observations of Gliese 1214b. Like the atmospheric envelope it hints at, the data is nuanced, as a subsequent follow-up observation failed to detect helium, leaving researchers uncertain why the signal did not repeat.
