Overview
- A peer-reviewed study published on June 24, 2026, reports two very low-density, Jupiter-size planets orbiting the star TOI-791 about 1,113 light-years away.
- The planets, named TOI-791 b and TOI-791 c, are roughly Jupiter-sized but contain only about 3.0 percent and 5.9 percent of Jupiter’s mass, respectively, giving densities near 0.038 and 0.047 grams per cubic centimeter.
- Researchers derived those unusually small masses by measuring transit-timing variations in multi-year TESS photometry and refining the results with complementary ASTEP observations from Antarctica.
- The team says the planets are likely dominated by hydrogen and helium, and they propose two main explanations: large primordial envelopes from formation far from the star or atmospheric inflation driven by stellar heating.
- Confirming the composition and testing formation models is now the priority, with targeted JWST follow-up planned to probe atmospheric gases and resolve how such rare “super‑puffs” can exist in one system.