Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b
Name
Benneke_2019_ApJL_887_L14.pdf
Description
Published version
Size
1.39 MB
Format
Adobe PDF
Checksum (MD5)
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Author(s)
Benneke, Björn
Wong, Ian
Piaulet, Caroline
Knutson, Heather A
Lothringer, Joshua
Morley, Caroline V
Gao, Peter
Greene, Thomas P
Dressing, Courtney
Dragomir, Diana
Date Issued
December 2019
Journal
Astrophysical Journal Letters
Publisher
American Astronomical Society
Citation
Benneke, Björn et al. "Water Vapor and Clouds on the Habitable-zone Sub-Neptune Exoplanet K2-18b." Astrophysical Journal Letters 887, 1 (December 2019): 887 © 2019 The American Astronomical Society
Version
Final published version
Abstract
Results from the Kepler mission indicate that the occurrence rate of small planets (<3 R ⊕) in the habitable zone of nearby low-mass stars may be as high as 80%. Despite this abundance, probing the conditions and atmospheric properties on any habitable-zone planet is extremely difficult and has remained elusive to date. Here, we report the detection of water vapor and the likely presence of liquid and icy water clouds in the atmosphere of the 2.6 R ⊕ habitable-zone planet K2-18b. The simultaneous detection of water vapor and clouds in the mid-atmosphere of K2-18b is particularly intriguing because K2-18b receives virtually the same amount of total insolation from its host star (1368+114-107 W m-2) as the Earth receives from the Sun (1361 W m-2), resulting in the right conditions for water vapor to condense and explain the detected clouds. In this study we observed nine transits of K2-18b using Hubble Space Telescope/WFC3 in order to achieve the necessary sensitivity to detect the water vapor, and we supplement this data set with Spitzer and K2 observations to obtain a broader wavelength coverage. While the thick hydrogen-dominated envelope we detect on K2-18b means that the planet is not a true Earth analog, our observations demonstrate that low-mass habitable-zone planets with the right conditions for liquid water are accessible with state-of-the-art telescopes.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Creative Commons Attribution 3.0 unported license
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.3847/2041-8213/AB59DC
