Astronomers Confirm Two Super‑Puff Jupiter‑Size Planets

Overview

• A study published Thursday, June 25, 2026, in Monthly Notices of the Royal Astronomical Society confirms two exoplanets, TOI‑791 b and TOI‑791 c, as “super‑puff” planets orbiting a star about 1,110 light‑years away.
• Both planets are roughly Jupiter‑sized but extremely low in mass, giving them densities far below Jupiter’s and comparable to cotton candy or shaving foam.
• The pair occupy a rare 5:3 mean‑motion resonance, meaning the inner planet completes five orbits for every three orbits of the outer planet, a configuration that helps measure their masses through transit timing variations.
• The discoveries began with TESS detections flagged by Planet Hunters TESS volunteers and were validated after eight years of global follow‑up observations, including telescopes at Concordia Station in Antarctica.
• Researchers say the planets are likely dominated by hydrogen and helium but the composition and origin story remain unconfirmed, so teams plan targeted JWST and other atmospheric studies to resolve how such puffed‑up giants form and evolve.