First results of Herschel/PACS observations of Neptune
E. Lellouch, P. Hartogh, H. Feuchtgruber, B. Vandenbussche, T. de, Graauw, R. Moreno, C. Jarchow, T. Cavali\'e, G. Orton, M. Banaszkiewicz, M.I., Blecka, D. Bockel\'ee-Morvan, J. Crovisier, T. Encrenaz, T. Fulton, M., K\"uppers, L.M. Lara, D.C. Lis, A.S. Medvedev, M. Rengel

TL;DR
This paper presents initial Herschel/PACS spectral observations of Neptune, revealing its thermal profile, isotopic ratios, and atmospheric composition, with implications for planetary formation and atmospheric processes.
Contribution
First detailed spectral analysis of Neptune using Herschel/PACS, providing new insights into its atmospheric composition and thermal structure.
Findings
Neptune's mean temperature is ~3 K warmer than Voyager data.
Deuterium enrichment in Neptune's atmosphere confirmed.
Stratospheric methane and water abundances quantified.
Abstract
We report on the initial analysis of a Herschel/PACS full range spectrum of Neptune, covering the 51-220 micrometer range with a mean resolving power of ~ 3000, and complemented by a dedicated observation of CH4 at 120 micrometers. Numerous spectral features due to HD (R(0) and R(1)), H2O, CH4, and CO are present, but so far no new species have been found. Our results indicate that (i) Neptune's mean thermal profile is warmer by ~ 3 K than inferred from the Voyager radio-occultation; (ii) the D/H mixing ratio is (4.5+/-1) X 10**-5, confirming the enrichment of Neptune in deuterium over the protosolar value (~ 2.1 X 10**-5); (iii) the CH4 mixing ratio in the mid stratosphere is (1.5+/-0.2) X 10**-3, and CH4 appears to decrease in the lower stratosphere at a rate consistent with local saturation, in agreement with the scenario of CH4 stratospheric injection from Neptune's warm south polar…
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