Two low density giant planets found orbiting the star TOI-791

Star system: TOI-791 | Distance from the Sun: 1097 light years

Two giant planets, TOI-791 b and TOI-791 c, have been confirmed orbiting the F7-type star TOI-791. Both planets are similar in size to Jupiter, but they possess exceptionally low densities. They follow long-period orbits, taking approximately 139 days and 232 days respectively to complete a revolution around their host star. The planets are locked in a orbital relationship known as a 5:3 resonance, which causes detectable timing shifts as they pass in front of their star.

The planets were observed using ground-based photometry, with the ASTEP telescope in Antarctica recording entire transits lasting over 11 hours. These represent the longest duration transit observations ever completed from the ground. By analyzing the timing variations in these transits, the researchers were able to calculate the masses of both worlds.

These mass measurements revealed that the planets are among the least dense giant planets ever identified. Their unique, puffy structure and long orbits provide significant data for understanding how giant planets form and migrate within solar systems. Future studies are planned to further map the complex gravitational interactions and overall architecture of this system.

Key findings
- TOI-791 b and c are among the lowest density giant planets currently known to science.
- The planets maintain a 5:3 orbital resonance, creating transit timing variations of up to 50 minutes.
- ASTEP observations captured the longest transits ever recorded in their entirety from a ground-based facility.
- TOI-791 b orbits in 139 days, while TOI-791 c takes 232 days to complete its path.
- Detailed analysis of transit timing variations allowed for the calculation of the planets' dynamical masses.

Scientific study

ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791 (external link)