Astronomy
The Search for Proxima b: Atmosphere and Habitability
Quick fact
Proxima b orbits in the habitable zone of its star, but it receives about 650 times more high-energy X-ray radiation than Earth, which could strip away its atmosphere within a billion years if unprotected.
Why this is interesting
Proxima b is the closest known exoplanet to us, but could it really host life? Its atmosphere—if it has one—might hold the answer.
Read the full explanation
Understanding The Search for Proxima b: Atmosphere and Habitability
Picture a small, cool star called a red dwarf. Proxima b orbits so close to it that it takes only 11 days to circle around, and it likely always shows the same face to its star—a phenomenon called tidal locking. Being in the 'habitable zone' means that, on a rocky world without an atmosphere, the temperature could allow liquid water on the surface. But that zone assumes the planet has an atmosphere to trap heat and distribute it. The star's violent flares and intense radiation pose a huge threat. Just as a balloon can pop with too much pressure, a planet's atmosphere can be blown away by the stellar wind if it lacks a protective magnetic field. So while Proxima b sits in the 'just right' zone, its habitability depends on whether it can keep its air.
A deeper explanation
The core mechanism is atmospheric retention. An atmosphere is held by gravity but eroded by stellar energy. Proxima b's gravity is similar to Earth's, so it can hold heavy gases. However, the red dwarf's frequent flares emit high-energy X-ray and ultraviolet radiation that heats the upper atmosphere, causing molecules to escape into space—a process called atmospheric escape. Over billions of years, this can strip a planet of its atmosphere, especially if it lacks a strong magnetic shield. Some models suggest that Proxima b could still retain a thick atmosphere if it started with plenty of volatiles. But no telescope has yet directly detected its atmosphere. Future instruments like the James Webb Space Telescope might capture light passing through the atmosphere during a transit, revealing its composition. So the search for Proxima b's habitability is fundamentally a question of its atmosphere's survival, and understanding this helps us assess how common life might be in the universe.