NASA’s James Webb Space Telescope has detected compelling evidence of an atmosphere on TOI-561 b, a rocky exoplanet orbiting extremely close to its star. The discovery challenges assumptions about which worlds can hold onto air, even under extreme conditions. This finding is significant because it expands the potential range of habitable environments beyond what was previously thought possible.
Extreme Conditions and Unexpected Density
TOI-561 b, located 280 light-years away, is just 1.5 times Earth’s width and completes an orbit in under 11 hours. Its proximity to its star—less than 1 million miles—results in a permanent day-night divide. The dayside likely experiences temperatures high enough to melt rock, creating a potential lava ocean.
Yet, what surprised researchers was the planet’s unusually low density. Johanna Teske, lead author of the study, notes that it’s “anomalously low,” suggesting it’s less dense than expected for a rocky planet with an Earth-like composition. This anomaly initially led scientists to consider whether the planet formed from unusual materials, given its star is old and relatively iron-poor.
Atmospheric Evidence from Heat Measurements
To investigate further, the team used Webb to measure the planet’s heat emissions during its transit behind the star. If TOI-561 b were a bare rock, the dayside should reach 4,900°F. Instead, Webb recorded a cooler temperature of 3,200°F—still scorching, but significantly lower.
Researchers determined that the only plausible explanation is a thick atmosphere. Anjali Piette, a coauthor on the study, stated they “really need a thick volatile-rich atmosphere to explain all the observations.” The atmosphere likely cools the planet by circulating heat and trapping gases like water vapor, potentially creating cloud cover that reflects sunlight.
Implications for Exoplanet Research
The existence of an atmosphere on such a hostile world suggests that even planets exposed to intense radiation can retain air. The team believes gases may cycle between a potential lava ocean and the atmosphere, allowing the planet to maintain its gaseous envelope.
The researchers plan further studies to map the planet’s surface temperatures and determine the atmospheric composition. This discovery broadens the scope of exoplanet research, indicating that habitable worlds may exist in environments previously considered uninhabitable.
The presence of an atmosphere on TOI-561 b demonstrates that rocky exoplanets under extreme conditions can retain air, significantly expanding the potential range of habitable worlds elsewhere in the galaxy.
