학술논문
Pluto's atmosphere from stellar occultations in 2012 and 2013
Document Type
Working Paper
Author
Dias-Oliveira, A.; Sicardy, B.; Lellouch, E.; Vieira-Martins, R.; Assafin, M.; Camargo, J. I. B.; Braga-Ribas, F.; Gomes-Júnior, A. R.; Benedetti-Rossi, G.; Colas, F.; Decock, A.; Doressoundiram, A.; Dumas, C.; Emilio, M.; Polleri, J. Fabrega; Gil-Hutton, R.; Gillon, M.; Girard, J.; Hau, G.; Ivanov, V. D.; Jehin, E.; Lecacheux, J.; Leiva, R.; Lopez-Sisterna, C.; Mancini, L.; Maury, A.; Meza, E.; Morales, N.; Nagy, L.; Opitom, C.; Ortiz, J. L.; Pollock, J.; Roques, F.; Snodgrass, C.; Soulier, J. F.; Thirouin, A.; Vanzi, L.; Widemann, T.; Reichart, D. E.; LaCluyze, A. P.; Haislip, J. B.; Ivarsen, K. M.; Dominik, M.; Jørgensen, U.; Skottfelt, J.
Source
Subject
Language
Abstract
We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves, twelve of them being used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no-haze) and pure N_2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that fits satisfactorily (i.e. within the noise level) all the twelve light-curves, providing atmospheric constraints between ~1,190 km (pressure ~ 11 \mubar) and ~ 1,450 km (pressure ~0.1 \mubar) from Pluto's center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with strong positive gradient between 1,190 km (at 36 K, 11 \mubar) and r = 1,215 km (6.0 \mubar), where a temperature maximum of 110 K is reached; above it is a mesosphere with negative thermal gradient of -0.2 K/km up to ~ 1,390 km (0.25 \mubar), where, the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6 %) but significant increase (6-\sigma level) between the two dates; (3) without troposphere, Pluto's radius is found to be R_P = 1,190 +/- 5km. Allowing for a troposphere, R_P is constrained to lie between 1,168 and 1,195 km; (4) the currently measured CO abundance is too small to explain the mesospheric negative thermal gradient. Cooling by HCN is possible, but only if this species is largely saturated; Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric trend.
Comment: 41 pages, 13 figures, 4 tables
Comment: 41 pages, 13 figures, 4 tables