Observations of Gliese 1132 b reveal a planet likely lacking an atmosphere

Star system: Gliese 1132 | Distance from the Sun: 41.1 light years

Recent analysis of data from the James Webb Space Telescope, the Hubble Space Telescope, and ground-based observations suggests that the exoplanet Gliese 1132 b is likely a bare rocky world. By examining the light filtering through the planet’s edges as it passes in front of its host star, the data reveals a featureless transmission spectrum, meaning no clear chemical fingerprints of an atmosphere were detected.

The study compared various models, including clear and cloudy atmospheres, against a flat-line scenario. While some models hinted at the possible presence of molecules like ammonia, these signals were weak and disappeared when certain outlier data points were removed from the analysis. The findings consistently point toward the absence of a substantial atmosphere.

To determine this, the research combined multiple transit observations—the brief dimming of a star when a planet passes in front of it—across a wide range of light wavelengths. This comprehensive approach allowed for testing complex atmospheric scenarios, ultimately favoring the interpretation of a rocky surface without a significant gaseous envelope.

While a very thin or obscured atmosphere cannot be entirely ruled out depending on how specific telescope measurements are interpreted, the most straightforward explanation supported by the current data is that Gliese 1132 b is a naked rocky planet with a radius approximately 1.13 times that of Earth.

Key findings
- Gliese 1132 b shows a featureless transmission spectrum, indicating no clear evidence of an atmosphere.
- The planet is best described as a bare rocky object with a radius of 1.129 Earth radii.
- Previous hints of water or ammonia in the atmosphere were found to be marginal and weakened upon closer inspection.
- Models testing for cloudy or clear atmospheres provided no evidence over the simpler flat-line scenario.

Scientific study

Atmospheric Retrieval of Combined JWST, HST, and Ground-Based Observations Reveals a Featureless Transmission Spectrum for GJ 1132 b (external link)