Publications (3)0 Total impact
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ABSTRACT: The atmospheric structure of Triton in the altitude range 25-150 kilometers shows an unexpectedly steep thermal gradient of 0.26 K per kilometer above 50 kilometer altitude, with a nearly isothermal profile below. The upper part of the profile can be explained by downward conduction of heat deposited by magnetospheric electrons and solar UV. However, the atmospheric temperature below 50 kilometers is too cold for identified radiative processes to dispose of the inferred heat flux (0.0012 erg per square centimeter per second) from the upper atmosphere. This implies that either the atmosphere is not in a steady state and/or an unidentified cooling mechanism is at work in the altitude range 25-50 kilometers. When extrapolated to the surface, the inversion results yield a pressure of 19.0 sup (+1.8) sub (-1.5), mubar, about 5mubar greater than that observed by Voyager.
02/1999;
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ABSTRACT: 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.
08/1998; 30:1107.
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[hide abstract]
ABSTRACT: The atmospheric structure of Triton in the altitude range 25–150 km shows an unexpectedly steep thermal gradient of 0.26 K km−1 above 50 km altitude, with a nearly isothermal profile below. The upper part of the profile can be explained by downward conduction of heat deposited by magnetospheric electrons and solar UV. However, the atmospheric temperature below 50 km is too cold for identified radiative processes to dispose of the inferred heat flux (0.0012 erg cm−2 s−1) from the upper atmosphere. This implies that either the atmosphere is not in a steady state and/or an unidentified cooling mechanism is at work in the altitude range 25–50 km. When extrapolated to the surface, the inversion results yield a pressure of 19.0−1.5+1.8 μbar, about 5 μbar greater than that observed by Voyager.
Icarus.
Institutions
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1998
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Lowell Observatory
Lowell,
MA,
USA
