The First Hubble Detection of a Secondary Eclipse from a Rocky Exoplanet: The 5.4 hr Planet TOI-2431 b
Year: 2026
Type: article
Abstract: We present a Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 phase-curve observation of the ultrashort-period rocky planet TOI-2431 b and detect its secondary eclipse in the near-infrared. Combined with the TESS optical eclipse, these measurements constrain the planet’s dayside brightness temperature, reflected light contribution, albedo, and heat redistribution. We detect the eclipse in the optical and near-infrared wavelengths of TESS and HST/WFC3 G141, with a planet-to-star flux ratio of 37 ± 10 ppm and 6 9 − 13 + 14 ppm , respectively. Assuming negligible reflected light, the joint TESS+HST fit yields a brightness temperature T b , joint = 252 4 − 84 + 77 K and a brightness temperature ratio of R joint = T b , joint / T p , max = 0.98 0 − 0.034 + 0.032 consistent with the zero-albedo, no-redistribution limit T p , max = 257 4 − 35 + 36 K . The HST phase curve is consistent with zero nightside emission and no measurable hotspot offset, consistent with inefficient day-night heat distribution. Under this thermal-dominated interpretation, TOI-2431 b lies at the zero-albedo, no-redistribution limit and contrasts with previously observed lava worlds. At optical and near-infrared wavelengths, however, thermal emission is degenerate with reflected light. For a geometric albedo of A g = 0.1, reflected light would contribute approximately 11 ppm in each bandpass, reducing the temperature to T b , joint ( A g = 0.1 ) = 240 7 − 102 + 91 K . Longer-wavelength observations are required to isolate the thermal co
Authors: Sebastian Zieba, Billy Edwards, Samuel N. Quinn, Leoni Janssen, Nicolas B. Cowan, Laura Kreidberg, Mercedes López-Morales, Lisa Dang, Luca Malavolta, Yamila Miguel, T. Giang Nguyen, Andrew Vanderburg, Thomas G. Wilson, Mantas Zilinskas, Nicholas J. Connors, Ian J. M. Crossfield, Oliver Herbort, Adam L. Kraus, Tim Lichtenberg, Mariana Sastre, Joost P. Wardenier
Institutions: Center for Astrophysics Harvard & Smithsonian, Space Research Organisation Netherlands, Leiden Observatory, McGill University, Max Planck Institute for Astronomy, Space Telescope Science Institute, University of Waterloo, University of Padua, Osservatorio Astronomico di Padova, National Institute for Astrophysics, Leiden University, University of Warwick, California Institute of Technology, Université de Montréal, University of Kansas, University of Vienna, The University of Texas at Austin, University of Groningen, University of Bern
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
OpenAlex ID: W7214788602