The Structure of Triton's Middle Atmosphere from HST Stellar Occultation Observations

Details The Structure of Triton's Middle Atmosphere from HST Stellar Occultation Observations The Structure of Triton's Middle Atmosphere from HST Stellar Occultation Observations

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998dps....30.4901e&link_type=abstract

American Astronomical Society, DPS meeting #30, #49.01; Bulletin of the American Astronomical Society, Vol. 30, p.1107

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Scientific paper

Triton's occultation of a 10.6 magnitude star was observed with FGS #3 aboard the HST, which passed close enough to the center of Triton's shadow to record a central flash. These data have been used to infer a substantial increase in Triton's surface pressure since the Voyager encounter in 1989 and a previous stellar occultation in 1995 (Olkin et al., Icarus 129, 178). Because the predominantly nitrogen atmosphere is in vapor-pressure equilibrium with surface frost, the surface-pressure increase implies a global warming of Triton's surface frost of 1-2 K over the 8-year period (Elliot et al., Nature 393, 765). Here we report results of inversions of these data to recover temperature, pressure, and number density profiles of Triton's atmosphere over an altitude range of 25-150 km. The upper part of the temperature profile shows a thermal gradient of ~ 0.3 K/km down to an altitude of ~ 50 km, where the profile becomes isothermal at a temperature of ~ 50-52 K. This result is somewhat warmer than the 48 K equivalent isothermal temperature reported by Tyler et al. (Science 246, 1466) in the 0-50 km altitude range. Atmospheric models based on Voyager data (e.g. Strobel et al., Icarus 120, 266; Krasnopolsky et al., JGR 98, 3065; Lellouch et al., Adv. Space Rev., {/bf 12}, 113) do not have a steep enough temperature gradient in the 25-150 km region, nor do they have an isothermal region below 50 km. Below this isothermal region the temperature must decrease to a surface-frost temperature of 39-40 K. This work was supported, in part, by STScI Grants GO-07489.01-96A at MIT and GO-07489.02-96A at Lowell Observatory.

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