Stellar activity impacts detection of carbon dioxide on planet TRAPPIST-1f

Star system: TRAPPIST-1 | Distance from the Sun: 40.7 light years

The TRAPPIST-1 system contains seven Earth-sized planets orbiting a red dwarf star. Studying their atmospheres using transmission spectroscopy—a method where starlight passes through a planet's atmosphere during a transit—is complicated by the star itself. Active regions on the stellar surface, such as starspots, can mimic or mask the signals of atmospheric gases, making it difficult to distinguish between the planet's actual composition and the star's own light variations.

Researchers evaluated the detectability of an atmosphere on TRAPPIST-1f, a planet located in the habitable zone, by accounting for these stellar disturbances. Using a simulation based on a carbon dioxide-rich environment, they tested how well the James Webb Space Telescope could identify gases despite the signal noise generated by the active red dwarf star. The study integrated models of the star's surface activity to determine if atmospheric features could still be reliably recovered.

The findings indicate that while carbon dioxide can be identified with approximately 10 transits, other gases like methane require around 50 transits to find even weak evidence. Water vapor remained undetectable even after 100 simulated transits. These results suggest that while short observation programs can confirm certain components, disentangling more subtle atmospheric signatures from the star's powerful light contamination requires significantly more time than previously estimated.

Key findings
- Detection of carbon dioxide is possible with 10 transits of TRAPPIST-1f.
- Methane provides only weak evidence after 50 transits.
- Water vapor remains elusive even after 100 simulated transits.
- Stellar contamination from the red dwarf host is stronger than anticipated, complicating atmospheric identification.
- Longer observation times are essential to overcome interference from stellar active regions.

Scientific study

Veiled in Starlight: Impacts of Stellar Contamination on Retrievals of TRAPPIST-1f's Atmospheric Composition (external link)