Investigating the Atmospheric Mass Loss of the Kepler-105 Planets Straddling the Radius Gap

February 2024 • 2024AJ....167...84H

Authors • Householder, Aaron • Weiss, Lauren M. • Owen, James E. • Isaacson, Howard • Howard, Andrew W. • Fabrycky, Daniel • Rogers, Leslie A. • Schlichting, Hilke E. • Fulton, Benjamin J. • Petigura, Erik A. • Giacalone, Steven • Murphy, Joseph M. Akana • Beard, Corey • Chontos, Ashley • Dai, Fei • Van Zandt, Judah • Lubin, Jack • Rice, Malena • Polanski, Alex S. • Dalba, Paul • Blunt, Sarah • Turtelboom, Emma V. • Rubenzahl, Ryan • Brinkman, Casey

Abstract • An intriguing pattern among exoplanets is the lack of detected planets between approximately 1.5 R _⊕ and 2.0 R _⊕. One proposed explanation for this "radius gap" is the photoevaporation of planetary atmospheres, a theory that can be tested by studying individual planetary systems. Kepler-105 is an ideal system for such testing due to the ordering and sizes of its planets. Kepler-105 is a Sun-like star that hosts two planets straddling the radius gap in a rare architecture with the larger planet closer to the host star (R _b = 2.53 ± 0.07 R _⊕, P _b = 5.41 days, R _c = 1.44 ± 0.04 R _⊕, P _c = 7.13 days). If photoevaporation sculpted the atmospheres of these planets, then Kepler-105b would need to be much more massive than Kepler-105c to retain its atmosphere, given its closer proximity to the host star. To test this hypothesis, we simultaneously analyzed radial velocities and transit-timing variations of the Kepler-105 system, measuring disparate masses of M _b = 10.8 ± 2.3 M _⊕ (ρ _b = 3.68 ± 0.84 g cm^‑3) and M _c = 5.6 ± 1.2 M _⊕ (ρ _c = 10.4 ± 2.39 g cm^‑3). Based on these masses, the difference in gas envelope content of the Kepler-105 planets could be entirely due to photoevaporation (in 76% of scenarios), although other mechanisms like core-powered mass loss could have played a role for some planet albedos.

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Benjamin Fulton

Assistant Scientist