Refining Saturn's deuterium-hydrogen ratio via IRTF/TEXES spectroscopy

Abstract

The abundance of deuterium in giant planet atmospheres provides constraints on the reservoirs of ices incorporated into these worlds during their formation and evolution. Motivated by discrepancies in the measured deuterium-hydrogen ratio (D/H) on Jupiter and Saturn, we present a new measurement of the D/H ratio in methane for Saturn from ground-based measurements. We analysed a spectral cube (covering 1151-1160 cm${}^{-1}$ from 6 February 2013) from the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA's Infrared Telescope Facility (IRTF) where emission lines from both methane and deuterated methane are well resolved. Our estimate of the D/H ratio in stratospheric methane, $1.65_{-0.21}^{+0.27}\times 10^{-5}$ is in agreement with results derived from Cassini CIRS and ISO/SWS observations, confirming the unexpectedly low CH${}_3$D abundance. Assuming a fractionation factor of $1.34\pm 0.19$ we derive a hydrogen D/H of $1.23_{-0.23}^{+0.27}\times 10^{-5}$. This value remains lower than previous tropospheric hydrogen D/H measurements of (i) Saturn $2.10(\pm 0.13)\times 10^{-5}$, (ii) Jupiter $2.6(\pm 0.7)\times 10^{-5}$ and (iii) the proto-solar hydrogen D/H of $2.1(\pm 0.5)\times 10^{-5}$, suggesting that the fractionation factor may not be appropriate for stratospheric methane, or that the D/H ratio in Saturn's stratosphere is not representative of the bulk of the planet.

arXiv comment9 pages, 6 figures, 1 table

References in corpus (8)

• The D/H ratio in the atmospheres of Uranus and Neptune from Herschel PACS observations
• Neptune's Atmospheric Composition from AKARI Infrared Spectroscopy
• The Origin of Nitrogen on Jupiter and Saturn from the ${}^{15}$N/${}^{14}$N Ratio
• Disruption of Saturn's Quasi-Periodic Equatorial Oscillation by the Great Northern Storm
• The D/H Ratio in Interstellar Gas Towards G191-B2B
• Giant Planet Observations with the James Webb Space Telescope
• The Hera Saturn Entry Probe Mission
• Stratospheric aftermath of the 2010 Storm on Saturn as observed by the TEXES instrument. I. Temperature structure

Cited by in corpus (3)

• Deuterated water ice on the satellites of Saturn
• Accurate reference spectra of HD in H${}_2$/He bath for planetary applications
• Mid-Infrared Observations of the Giant Planets