Overview
- A University of Oxford‑led study published June 25, 2026 confirmed two new “super‑puff” planets, TOI‑791 b and TOI‑791 c, using long‑baseline TESS data and an international follow‑up campaign.
- The planets are roughly the size of Jupiter but have only about 3.0% and 5.9% of Jupiter’s mass, giving them the lowest densities measured for objects of their size.
- Astronomers measured those tiny masses by tracking transit timing variations produced as the planets tug on each other and by combining TESS with ground telescopes including ASTEP in Antarctica.
- The two bodies orbit with long periods of about 139 days and 232 days and are locked in a 5:3 mean‑motion resonance, a rare configuration that produced the timing signal used to confirm their masses.
- The system is now a high‑priority target for JWST and continued dynamical monitoring because its hydrogen/helium‑dominated envelopes, origin, and evolution could overturn standard planet‑formation models.