Pluto's lower atmosphere and pressure evolution from ground-based stellar occultations, 1988-2016

Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 μbar to 10 nbar). Results. (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4–7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere

Lower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988-2016

Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ∼5 and ∼380 km (i.e. pressures from ∼10 μbar to 10 nbar). Results. (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ∼0.3 are present at 4-7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ∼20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.Fil: Meza, E.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Sicardy, B.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Assafin, M.. Observatório do Valongo; Brasil. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Ortiz, J.L.. Instituto de Astrofísica de Andalucía; EspañaFil: Bertrand, T.. National Aeronautics and Space Administration; Estados UnidosFil: Lellouch, E.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Desmars, J.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Forget, F.. Laboratoire de Meteorologie Dynamique; Francia. Sorbonne University; Francia. Universite de Paris VI; Francia. Centre National de la Recherche Scientifique; FranciaFil: Bérard, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Doressoundiram, A.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Lecacheux, J.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Marques Oliveira, J.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Roques, F.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Widemann, T.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Colas, F.. National Aeronautics and Space Administration; Estados UnidosFil: Vachier, F.. National Aeronautics and Space Administration; Estados UnidosFil: Renner, S.. National Aeronautics and Space Administration; Estados Unidos. Observatoire de Lille; FranciaFil: Leiva, R.. Southwest Research Institute.; Estados UnidosFil: Braga Ribas, F.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Universidade Tecnologia Federal do Parana; BrasilFil: Benedetti Rossi, G.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Camargo, J. I. B.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Dias Oliveira, A.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Morgado, B.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Gomes Júnior, A. R.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Vieira Martins, R.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Behrend, R.. Geneva Observatory; ItaliaFil: Castro Tirado, A.. Instituto de Astrofísica de Andalucía; EspañaFil: Duffard, R.. Instituto de Astrofísica de Andalucía; EspañaFil: Morales, N.. Instituto de Astrofísica de Andalucía; EspañaFil: Gil Hutton, Ricardo Alfredo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin