A secondary atmosphere on the rocky exoplanet 55 Cancri e.
basic_science · Level V
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- Record sourced from PubMed, PMID 38718834.
- Also identified by DOI 10.1038/s41586-024-07432-x.
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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<sup>1-3</sup> or inconclusive results<sup>4-6</sup>. The 1.95R<sub>Earth</sub> and 8.8M<sub>Earth</sub> 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<sup>7-13</sup>. The planet has been observed extensively with transmission spectroscopy<sup>14-22</sup> and its thermal emission has been measured in broad photometric bands<sup>23-26</sup>. These observations disfavour a primordial H<sub>2</sub>/He-dominated atmosphere but cannot conclusively determine whether the planet has a secondary atmosphere<sup>27,28</sup>. 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<sup>29-32</sup> and indicate a bona fide volatile atmosphere that is probably rich in CO<sub>2</sub> or CO. This atmosphere can be outgassed from and sustained by a magma ocean.