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

Creators: Householder, Aaron; Weiss, Lauren M.; Owen, James E.; Isaacson, Howard; Howard, Andrew W.¹; 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

1. California Institute of Technology

Abstract

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.

Copyright and License

© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank the anonymous referee whose insights and suggestions significantly enhanced the quality of this manuscript.

This material is based on work supported by the National Science Foundation REU Program (grant No. 2050527). A.H. thanks Beatriz Campos Estrada, Greg Laughlin, Andrew W. Mayo, and the Astroweiss group for useful conversations and feedback. A.H. also thanks Jason Rowe for generously sharing the transit times used in this paper. We are also grateful to Miki Nakajima for her contributions to the proposal that enabled the acquisition of the RV data presented in this work.

L.M.W. acknowledges support from the NASA-Keck Key Strategic Mission Support program (grant No. 80NSSC19K1475) and the NASA Exoplanet Research Program (grant no. 80NSSC23K0269). R.A.R. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. J.M.A.M. acknowledges support from the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1842400 and from NASAS Interdisciplinary Consortia for Astrobiology Research (NNH19ZDA001N-ICAR) under award number 19-ICAR19_2-0041. This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to (1) the University of Hawai'i, and (2) the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors also wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Facilities

Kepler - The Kepler Mission, Keck:I -

Software References

RadVel (Fulton et al. 2018), TTVFaster (Agol & Deck 2016), TTVFast (Deck et al. 2014), NumPy (van der Walt et al. 2011), Matplotlib (Hunter 2007), Pandas (McKinney 2010)

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