A secondary atmosphere on the rocky Exoplanet 55 Cancri e

Creators: Hu, Renyu; Bello-Arufe, Aaron; Zhang, Michael; Paragas, Kimberly; Zilinskas, Mantas; van Buchem, Christiaan; Bess, Michael; Patel, Jayshil; Ito, Yuichi; Damiano, Mario; Scheucher, Markus; Oza, Apurva V.; Knutson, Heather A.¹; Miguel, Yamila; Dragomir, Diana; Brandeker, Alexis; Demory, Brice-Olivier

1. California Institute of Technology

Abstract

Characterizing rocky exoplanets is a central aim of astronomy, and yet the search for atmospheres on rocky exoplanets has so far resulted in either tight upper limits on the atmospheric mass or inconclusive results. The 1.95R_Earth and 8.8M_Earth planet 55 Cancri e (abbreviated 55 Cnc e), with a predominantly rocky composition and an equilibrium temperature of around 2,000 K, may have a volatile envelope (containing molecules made from a combination of C, H, O, N, S and P elements) that accounts for up to a few percent of its radius. The planet has been observed extensively with transmission spectroscopy and its thermal emission has been measured in broad photometric bands. These observations disfavour a primordial H₂/He-dominated atmosphere but cannot conclusively determine whether the planet has a secondary atmosphere. Here we report a thermal emission spectrum of the planet obtained by the NIRCam and MIRI instruments aboard the James Webb Space Telescope (JWST) from 4 to 12 μm. The measurements rule out the scenario in which the planet is a lava world shrouded by a tenuous atmosphere made of vaporized rock and indicate a bona fide volatile atmosphere that is probably rich in CO₂ or CO. This atmosphere can be outgassed from and sustained by a magma ocean.

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Acknowledgement

We thank F. Gaillard for helpful discussion on magma ocean outgassing and J. Inglis for helpful discussion on data reduction with the James Webb Space Telescope (JWST). This research is based on observations with the NASA/ESA/CSA JWST obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-03127. These observations are associated with programme no. JWST-GO-1952. Support for programme no. JWST-GO-1952 was provided through a grant from the STScI under NASA contract NAS 5-03127. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Part of the high-performance computing resources used in this investigation were provided by funding from the JPL Information and Technology Solutions Directorate. M.Zh. acknowledges support from the 51 Pegasi b Fellowship financed by the Heising-Simons Foundation. Y.M. and M.Zi. have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101088557, N-GINE). Y.M. and C.v.B. acknowledge the support of a Dutch Science Foundation (NWO) Planetary and Exoplanetary Science (PEPSci) grant. B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046.

Data Availability

The data used in this paper are associated with JWST guest observer programme 1952 and are available from the Mikulski Archive for Space Telescopes (https://mast.stsci.edu). The data products required to generate Figs. 1–3 and Extended Data Figs. 1–9, as well as the stellar spectrum and the data reduction configuration files for the Eureka! – reduction 1 and SPARTA analyses are available at https://osf.io/2s6md/ with doi 10.17605/OSF.IO/2S6MD. All further data are available on request.