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5h ago

TESS Confirms Two Jupiter‑Sized Super‑Puff Planets

A peer‑reviewed study reports record‑low densities measured from transit‑timing variations using unique Antarctic transit observations, prompting proposals for JWST atmospheric spectroscopy.

Image
Image
Illustration of the giant planets TOI-791 b and TOI-791 c with host star TOI-791. These planets are roughly the size of Jupiter but a tiny fraction of its mass, meaning they have an extraordinarily low density. Image credit: NASA/Daniel Rutter.

Overview

  • The study, published June 25, 2026, confirms two exoplanets orbiting the star TOI‑791 as 'super‑puffs' and reports their discovery after seven years of TESS observations and coordinated follow-up.
  • TOI‑791 b and TOI‑791 c are roughly the size of Jupiter but have tiny masses—about 3.0% and 5.9% of Jupiter’s mass respectively—giving them densities lower than candy floss.
  • Scientists measured those low masses from transit‑timing variations caused by the planets tugging on each other and used continuous 11+ hour ground observations from ASTEP in Antarctica to capture full transits.
  • The pair are locked in a rare 5:3 mean‑motion resonance, a dynamical relationship that made the timing shifts measurable and places the system among only a handful known to host multiple super‑puff worlds.
  • Researchers say the system is a rare laboratory for planet‑formation studies and have proposed JWST spectroscopy to probe atmospheric composition and test whether the planets formed far out in the disk and migrated inward.