Key facts
- Helium has been observed escaping the atmosphere of exoplanet LHS 1140b.
- The helium loss suggests a lack of hydrogen in the planet's atmosphere.
- The rate of helium escape indicates that heavier elements are retained.
- The exoplanet system is located about 50 light-years away.
- The findings help define the 'cosmic shoreline' for the exoplanet system.
Astronomers have detected helium escaping the atmosphere of the exoplanet LHS 1140b, a rocky planet located approximately 50 light-years away. The study, published in Nature, used near-infrared imaging to observe helium in tails extending from the planet as it orbited its host star, LHS 1140a. This observation suggests that the high-energy radiation from the red dwarf star is driving helium out of the atmosphere.
The rate of helium loss, estimated at about 100,000 kilograms per second, implies that the planet's initial atmosphere was about 1.5% of its total mass. Crucially, the significant loss of helium indicates that there is little to no hydrogen remaining in the atmosphere, as hydrogen would typically shield helium from stellar radiation. The researchers infer that only elements with an atomic mass above nine would be unable to escape the atmosphere, meaning heavier elements like oxygen and nitrogen, as well as molecules like water and ammonia, would likely be retained.
This finding helps to define the 'cosmic shoreline' for the LHS 1140 system, distinguishing between regions where stellar radiation strips away atmospheres and where they can remain stable over billions of years. The data suggests that LHS 1140b is on the side where atmospheres can be stable, despite the ongoing loss of helium.