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Published May 25, 2023 | public
Journal Article Metadata-only

A temperate Earth-sized planet with tidal heating transiting an M6 star

Peterson, Merrin S. ORCID icon
Benneke, Björn ORCID icon
Collins, Karen ORCID icon
Piaulet, Caroline ORCID icon
Crossfield, Ian J. M. ORCID icon
Ali-Dib, Mohamad ORCID icon
Christiansen, Jessie L. ORCID icon
Gagné, Jonathan ORCID icon
Faherty, Jackie ORCID icon
Kite, Edwin ORCID icon
Dressing, Courtney ORCID icon
Charbonneau, David ORCID icon
Murgas, Felipe ORCID icon
Cointepas, Marion
Almenara, Jose Manuel ORCID icon
Bonfils, Xavier ORCID icon
Kane, Stephen ORCID icon
Werner, Michael W. ORCID icon
Gorjian, Varoujan ORCID icon
Roy, Pierre-Alexis ORCID icon
Shporer, Avi ORCID icon
Pozuelos, Francisco J. ORCID icon
Socia, Quentin Jay ORCID icon
Cloutier, Ryan ORCID icon
Dietrich, Jeremy ORCID icon
Irwin, Jonathan
Weiss, Lauren ORCID icon
Waalkes, William ORCID icon
Berta-Thomson, Zach
Evans, Thomas ORCID icon
Apai, Daniel ORCID icon
Parviainen, Hannu ORCID icon
Pallé, Enric ORCID icon
Narita, Norio ORCID icon
Howard, Andrew W. ORCID icon
Dragomir, Diana ORCID icon
Barkaoui, Khalid ORCID icon
Gillon, Michaël ORCID icon
Jehin, Emmanuel ORCID icon
Ducrot, Elsa ORCID icon
Benkhaldoun, Zouhair ORCID icon
Fukui, Akihiko ORCID icon
Mori, Mayuko ORCID icon
Nishiumi, Taku ORCID icon
Kawauchi, Kiyoe ORCID icon
Ricker, George ORCID icon
Latham, David W. ORCID icon
Winn, Joshua N. ORCID icon
Seager, Sara ORCID icon
Isaacson, Howard ORCID icon
Bixel, Alex
Gibbs, Aidan
Jenkins, Jon M. ORCID icon
Smith, Jeffrey C. ORCID icon
Pérez Chávez, José ORCID icon
Rackham, Benjamin V. ORCID icon
Henning, Thomas ORCID icon
Gabor, Paul
Chen, Wen-Ping ORCID icon
Espinoza, Néstor ORCID icon
Jensen, Eric L. N. ORCID icon
Collins, Kevin I. ORCID icon
Schwarz, Richard P. ORCID icon
Conti, Dennis M. ORCID icon
Wang, Gavin ORCID icon
Kielkopf, John F. ORCID icon
Mao, Shude ORCID icon
Horne, Keith ORCID icon
Sefako, Ramotholo ORCID icon
Quinn, Samuel N. ORCID icon
Moldovan, Dan ORCID icon
Fausnaugh, Michael ORCID icon
Fűűrész, Gábor ORCID icon
Barclay, Thomas ORCID icon

Abstract

Temperate Earth-sized exoplanets around late-M dwarfs offer a rare opportunity to explore under which conditions planets can develop hospitable climate conditions. The small stellar radius amplifies the atmospheric transit signature, making even compact secondary atmospheres dominated by N₂ or CO₂ amenable to characterization with existing instrumentation. Yet, despite large planet search efforts, detection of low-temperature Earth-sized planets around late-M dwarfs has remained rare and the TRAPPIST-1 system, a resonance chain of rocky planets with seemingly identical compositions, has not yet shown any evidence of volatiles in the system. Here we report the discovery of a temperate Earth-sized planet orbiting the cool M6 dwarf LP 791-18. The newly discovered planet, LP 791-18d, has a radius of 1.03 ± 0.04 R_⊕ and an equilibrium temperature of 300–400 K, with the permanent night side plausibly allowing for water condensation. LP 791-18d is part of a coplanar system4 and provides a so-far unique opportunity to investigate a temperate exo-Earth in a system with a sub-Neptune that retained its gas or volatile envelope. On the basis of observations of transit timing variations, we find a mass of 7.1 ± 0.7 M_⊕ for the sub-Neptune LP 791-18c and a mass of 0.9^(+0.5)_(−0.4) M_⊕ for the exo-Earth LP 791-18d. The gravitational interaction with the sub-Neptune prevents the complete circularization of LP 791-18d's orbit, resulting in continued tidal heating of LP 791-18d's interior and probably strong volcanic activity at the surface.

Additional Information

© 2023 Springer Nature. This work is based principally on observations made with the Spitzer Space Telescope (Spitzer DDT-14309, principal investigator, Benneke), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The material presented here is based on work supported in part by NASA under contract no. NNX15AI75G. B.B. and M.S.P. acknowledge financial support by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds de Recherche Québécois—Nature et Technologie (FRQNT; Québec). We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center, obtained from the Mikulski Archive for Space Telescopes data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. Resources supporting this work were provided by the NASA High-End Computing Program through the NASA Advanced Supercomputing Division at Ames Research Center for the production of the SPOC data products. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract no. NAS 5–26555. This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program. The Mid-Scale Innovations Program is supported by the National Science Foundation. This paper includes data taken from the EDEN telescope network, and we acknowledge support from the Earths in Other Solar Systems Project and Alien Earths (grant nos. NNX15AD94G and 80NSSC21K0593) sponsored by NASA. We acknowledge funding from the European Research Council (ERC) under the grant agreement no. 337591-ExTrA. This research has made use of the ExoFOP, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. R.C. is supported by a grant from the National Aeronautics and Space Administration in support of the TESS science mission. The MEarth Team gratefully acknowledges funding from the David and Lucile Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based on work supported by the National Science Foundation under grant nos. AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award) and AST-1616624. This work is made possible by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is based on work supported by the National Aeronautics and Space Administration under grant no. 80NSSC18K0476 issued through the XRP Program. M.S.P. and C.P. acknowledge support from FRQNT Master's and PhD scholarships. We acknowledge support from the Earths in Other Solar Systems Project, grant no. 3013511 sponsored by NASA. The results reported herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science research coordination network sponsored by NASA's Science Mission Directorate. The research leading to these results has received funding from the Australian Research Council (ARC) grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. TRAPPIST is supported by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant no. FRFC 2.5.594.09.F. TRAPPIST-North is a project supported by the University of Liège (Belgium), in collaboration with Cadi Ayyad University of Marrakech (Morocco). M.G. is F.R.S.-FNRS Research Director and E.J. is F.R.S.-FNRS Senior Research Associate. Resources supporting this work were provided by the NASA High-End Computing Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. The VATT referenced herein refers to the Vatican Observatory's Alice P. Lennon Telescope and Thomas J. Bannan Astrophysics Facility. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (grant no. FP/2007-2013) ERC grant agreement no 336480, from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation, from a research grant from the Balzan Prize Foundation, and funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 803193/BEBOP), from the Mobilising European Research in Astrophysics and Cosmology foundation, and from the Science and Technology Facilities Council (grant no. ST/S00193X/1). This work is partly supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant nos. JP17H04574, JP18H05439, Grant-in-Aid for JSPS Fellows, grant no. JP20J21872, Japan Science and Technolocy (JST) PRESTO grant no. JPMJPR1775, JST CREST grant no. JPMJCR1761 and the Astrobiology Center of National Institutes of Natural Sciences (grant no. AB031010). This article is based on observations made with the MuSCAT2 instrument, developed by the Astrobiology Center (ABC), at Telescopio Carlos Sánchez operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. F.J.P. acknowledges financial support from the grant no. CEX2021-001131-S supported by MCIN/AEI/10.13039/501100011033. R.C. acknowledges support from the Banting fellowship. Contributions. B.B. and M.S.P. conceived the project and wrote the manuscript. M.S.P. and B.B. carried out the main data analysis. C.P. and B.B. performed the tidal heating analysis. M.A.-D. performed the N-body integrations. J.G. performed the stellar characterization with the IRTF–SpeX Prism spectrum observed by J.F. V.G., B.B., I.J.M.C., J.L.C., C.D., T.E., A.W.H., S.K., M.W.W. and D.D. planned and implemented the Spitzer observations. Ground-based transit observations were executed and analysed by K.C., M.S.P., B.B., D.C., F.M., M.C., J.M.A., X.B., A.S., F.J.P., Q.J.S, J.D., J.I., W.W., Z.B.-T., D.A., H.P., E.P., N.N., M.G., E.J., E.D., Z.B., A.F., M.M., T.N. and K.K. P.-A.R., C.P., B.B. and R.C. modelled the mass-loss timescales. E.K. informed the discussion section. TESS observations were made possible by G.R., D.W.L., J.N.W., S.S., H.I., A.B., A.G., J.M.J., J.C.S., J.P.C., B.V.R., T.H., P.G., W.-P.C., N.E., E.L.N.J., K.I.C., R.P.S., D.M.C., G.W., J.F.K., S.M., K.H., R.S., S.N.Q., D.M., M.F., G.F. and T.B. All coauthors provided comments and suggestions on the manuscript. Data availability. The Spitzer data used in this study are publicly available at the Spitzer Heritage Archive, https://sha.ipac.caltech.edu/applications/Spitzer/SHA. The ground-based telescope observations are uploaded to ExoFOP and are publicly available. Source data are provided with this paper. Code availability. We fit the light-curve data using the open-source tools emcee and batman, available at https://github.com/dfm/emcee and https://github.com/lkreidberg/batman. The TTVs are modelled using the open-source tool TTVFast, available at https://github.com/kdeck/TTVFast, and are also fit using emcee. We obtain the constraints on planet compositions using the open-source tool smint, available at https://github.com/cpiaulet/smint. The tidal heating energy balance calculations are performed with the open-source tool melt, available at https://github.com/cpiaulet/melt. The authors declare no competing interests.

Additional details

Identifiers Funding Dates Caltech Custom Metadata
Created:
August 22, 2023
Modified:
October 20, 2023