Searching for GEMS: TOI-5916 b & TOI-6158 b are two Saturn-density planets orbiting M2 dwarfs

POSTER

Abstract

We confirm the planetary nature of (1) TOI-5916 b and (2) TOI-6158 b, two Exoplanets Transiting M-dwarf Stars (GEMS), both discovered by the Transiting Exoplanet Survey Satellite (TESS). Both systems were confirmed with ground-based photometry (Red Buttes Observatory and Swope, respectively) and radial velocity data from the Habitable-zone Planet Finder. Their radii are R₁ = 11.8 (+0.52 / −0.51) R⊕ and R₂ = 10.4 (+2.70 / −1.11) R⊕, and masses are M₁ = 219 ± 28 M⊕ and M₂ = 135 (+19 / −18) M⊕. Both planets have Saturn-like densities (ρ₁ = 0.73 (+0.14 / −0.13) g cm⁻³, ρ₂ = 0.66 (+0.41 / −0.23) g cm⁻³), which appears to be a growing trend among GEMS systems and, more generally, warm Jupiters. In confirming both of these exoplanets, we add to the growing evidence for a population of Saturn-density planets among the GEMS systems. We also find evidence for a preliminary trend in which GEMS exhibit systematically closer orbits compared to FGK giants. 

*Observations were obtained with the Habitable-zone Planet Finder (HPF) on the HET. The HPF team acknowledges support from NSF grants AST-1006676, AST-1126413, AST-1310885, AST-1517592, AST-1310875, ATI-2009889, ATI-2009982, AST-2108512, ATI-2009554, the NASA Astrobiology Institute (NNA09DA76A), and the Heising-Simons Foundation (2017-0494). This work was supported by NASA grant 80NSSC25K0184 as part of the U.S. Contributions to Ariel Preparatory Science (USCAPS) Program. Observations also used the NN-EXPLORE Exoplanet and Stellar Speckle Imager (NESSI), funded by the NASA Exoplanet Exploration Program and NASA Ames Research Center (Program ID: 2023B-438370). Data from MAST at STScI were used, supported by NASA grant NNX09AF08G. This includes public data from the TESS mission, funded by the NASA Science Mission Directorate.

Publication: https://arxiv.org/abs/2510.11798

Submitted to AAS Journals (AJ), awaiting review.

Presenters

  • Shane O'Brien

    • University of California, Irvine

Authors

  • Shane O'Brien

    • University of California, Irvine

  • Amber Wong

    • University of California, Irvine

  • Te Han

    • University of California, Irvine

  • Paul Robertson

    • University of California, Irvine

  • Shubham Kanodia

    • Earth and Planets Laboratory, Carnegie Institution for Science

  • Caleb I Cañas

    • NASA Goddard Space Flight Center