Astronomers confirmed the discovery of TOI-791 b and TOI-791 c, two Jupiter-sized exoplanets with densities of 0.038 and 0.047 g/cm³, respectively, making them the lowest-density giant planets ever detected[1][7]. Orbiting a star 1,113 light-years away in the constellation Volans, these super-puffs contain just 3% and 5.9% of Jupiter’s mass despite matching its radius[1][16]. The University of Oxford-led team, utilizing seven years of NASA TESS data, published findings in Monthly Notices of the Royal Astronomical Society on 26 June 2026[1][10]. Their existence challenges standard planetary formation models, suggesting either unusually thick hydrogen-helium envelopes or low-density core structures dominated by water ice[1][17]. Follow-up characterization by the James Webb Space Telescope is required to confirm chemical composition[1][16].