Bayesian analysis shows LTT 1445A b may lack a thick atmosphere

Star system: Gliese 3192 A | Distance from the Sun: 22.4 light years

LTT 1445A b is a rocky planet orbiting a red dwarf star, and astronomers are using the James Webb Space Telescope to search for signs of an atmosphere. This study introduces a new method that uses climate models and Bayesian statistics to analyze eclipse spectra, which are measurements of the planet’s heat as it passes behind its star. The method fits the observed data with models that account for the planet’s temperature and possible atmospheric composition, providing more reliable results than previous approaches.

Applying this method to JWST’s MIRI observations of LTT 1445A b, the researchers found that the data can be explained without needing an atmosphere, meaning a bare rock model fits well. If the planet does have an atmosphere, the study sets strict upper limits on how much gas could be present. For example, the surface pressure of oxygen, nitrogen, or carbon monoxide cannot be more than about one bar, carbon dioxide is limited to about one-tenth of a bar, water vapor to less than one-thousandth of a bar, and sulfur dioxide to less than one ten-thousandth of a bar. Future JWST observations may be able to detect thicker atmospheres if they exist.

This approach provides a way to turn eclipse spectra into quantitative constraints on exoplanet atmospheres, helping scientists test ideas about which planets can keep their atmospheres over time.

Key findings
- New Bayesian method constrains atmospheres of rocky exoplanets using JWST data.
- LTT 1445A b’s data are consistent with a bare rock, with no thick atmosphere required.
- Strict upper limits set for possible atmospheric gases.
- Future JWST observations could detect thicker atmospheres if present.
- Method helps test theories about atmospheric retention on exoplanets.

Scientific study

A Climate-Constrained Bayesian Inverse Method for JWST Rocky Exoplanet Eclipse Spectra: A Case Study of LTT 1445A b (external link)