Measuring the D/H Ratios of Exoplanets and Brown Dwarfs

Caroline V. Morley, Andrew J. Skemer, Brittany E. Miles, Michael R. Line, Eric D. Lopez, Matteo Brogi, Richard S. Freedman, Mark S. Marley

Research output: Contribution to journalArticle

Abstract

The relative abundance of deuterium and hydrogen is a potent tracer of planet formation and evolution. Jupiter and Saturn have protosolar atmospheric D/H ratios, a relic of substantial gas accretion from the nebula, while the atmospheres of Neptune and Uranus are enhanced in D by accretion of ices into their envelopes. For terrestrial planets, D/H ratios are used to determine the mechanisms of volatile delivery and subsequent atmosphere loss over the lifetime of the planet. Planets and brown dwarfs more massive than ∼13 M J quickly fuse their initial D reservoir. Here, we simulate spectra for giant exoplanets and brown dwarfs (2 M Neptune to ∼10 M Jupiter) from T eff = 200-1800 K including both CH3D and HDO to determine the observability of these dominant deuterium isotopologues in mid-infrared thermal emission spectra. Colder objects have stronger molecular features in their spectra, due to the temperature dependence of molecular cross sections. CH3D is easier to observe than HDO at all temperatures considered, due to the strength of its absorption bands and locations of features at wavelengths with few other strong absorption features. We predict that for nearby cool brown dwarfs, the CH3D abundance can be measured at high signal to noise with the James Webb Space Telescope (JWST); for objects from 200 to 800 K closer than 10 pc, a protosolar D/H ratio would be readily observable in 2.5 hr. Moderately young Jupiter-mass planets (100-300 Myr) and young Neptunes (10 Myr) may be discovered with JWST and provide the best targets for detecting deuterium on an exoplanet in the coming decade. Future telescope designs should consider the importance of isotopes for understanding the formation and evolution of planetary atmospheres.

Original languageEnglish (US)
Article numberL29
JournalAstrophysical Journal Letters
Volume882
Issue number2
DOIs
StatePublished - Sep 10 2019
Externally publishedYes

Fingerprint

extrasolar planets
Neptune (planet)
planets
planet
Jupiter (planet)
Neptune
deuterium
James Webb Space Telescope
Jupiter
atmospheres
Uranus (planet)
planetary atmospheres
terrestrial planets
accretion
fuses
Saturn
thermal emission
nebulae
planetary atmosphere
Uranus

Keywords

  • brown dwarfs
  • planets and satellites: atmospheres
  • planets and satellites: gaseous planets

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Morley, C. V., Skemer, A. J., Miles, B. E., Line, M. R., Lopez, E. D., Brogi, M., ... Marley, M. S. (2019). Measuring the D/H Ratios of Exoplanets and Brown Dwarfs. Astrophysical Journal Letters, 882(2), [L29]. https://doi.org/10.3847/2041-8213/ab3c65

Measuring the D/H Ratios of Exoplanets and Brown Dwarfs. / Morley, Caroline V.; Skemer, Andrew J.; Miles, Brittany E.; Line, Michael R.; Lopez, Eric D.; Brogi, Matteo; Freedman, Richard S.; Marley, Mark S.

In: Astrophysical Journal Letters, Vol. 882, No. 2, L29, 10.09.2019.

Research output: Contribution to journalArticle

Morley, CV, Skemer, AJ, Miles, BE, Line, MR, Lopez, ED, Brogi, M, Freedman, RS & Marley, MS 2019, 'Measuring the D/H Ratios of Exoplanets and Brown Dwarfs', Astrophysical Journal Letters, vol. 882, no. 2, L29. https://doi.org/10.3847/2041-8213/ab3c65
Morley, Caroline V. ; Skemer, Andrew J. ; Miles, Brittany E. ; Line, Michael R. ; Lopez, Eric D. ; Brogi, Matteo ; Freedman, Richard S. ; Marley, Mark S. / Measuring the D/H Ratios of Exoplanets and Brown Dwarfs. In: Astrophysical Journal Letters. 2019 ; Vol. 882, No. 2.
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