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

E. Meza, B. Sicardy, M. Assafin, J. L. Ortiz, T. Bertrand, E. Lellouch, J. Desmars, F. Forget, D. Bérard, A. Doressoundiram, J. Lecacheux, J. Marques Oliveira, F. Roques, T. Widemann, F. Colas, F. Vachier, S. Renner, R. Leiva, F. Braga-Ribas, G. Benedetti-Rossi, J. I. B. Camargo, A. Dias-Oliveira, B. Morgado, A. R. Gomes-Júnior, R. Vieira-Martins, R. Behrend, A. J. Castro-Tirado, R. Duffard, N. Morales, P. Santos-Sanz, M. Jelínek, R. Cunniffe, R. Querel, M. Harnisch, R. Jansen, A. Pennell, S. Todd, V. D. Ivanov, C. Opitom, M. Gillon, E. Jehin, J. Manfroid, J. Pollock, D. E. Reichart, J. B. Haislip, K. M. Ivarsen, A. P. LaCluyze, A. Maury, R. Gil-Hutton, V. Dhillon, S. Littlefair, T. Marsh, C. Veillet, K. -L. Bath, W. Beisker, H. -J. Bode, M. Kretlow, D. Herald, D. Gault, S. Kerr, H. Pavlov, O. Faragó, O. Klös, E. Frappa, M. Lavayssičre, A. Cole, A. B. Giles, J. G. Greenhill, K. M. Hill, M. W. Buie, C. B. Olkin, E. F. Young, L. A. Young, L. H. Wasserman, M. Devogčle, R. G. French, F. B. Bianco, F. Marchis, N. Brosch, S. Kaspi, D. Polishook, I. Manulis, M. Ait Moulay Larbi, Z. Benkhaldoun, A. Daassou, Y. El Azhari, Y. Moulane, J. Broughton, J. Milner, T. Dobosz, G. Bolt, B. Lade, A. Gilmore, P. Kilmartin, W. H. Allen, P. B. Graham, B. Loader, G. McKay, J. Talbot, S. Parker, L. Abe, P. Bendjoya, J.-P. Rivet, D. Vernet, L. Di Fabrizio, V. Lorenzi, A. Magazzú, E. Molinari, K. Gazeas, L. Tzouganatos, A. Carbognani, G. Bonnoli, A. Marchini, G. Leto, R. Sanchez, L. Mancini, B. Kattentidt, M. Dohrmann, K. Guhl, W. Rothe, K. Walzel, G. Wortmann, A. Eberle, D. Hampf, J. Ohlert, G. Krannich, G. Murawsky, B. Gährken, D. Gloistein, S. Alonso, A. Román, J. -E. Communal, F. Jabet, S. deVisscher, J. Sérot, T. Janik, Z. Moravec, P. Machado, A. Selva, C. Perelló, J. Rovira, M. Conti, R. Papini, F. Salvaggio, A. Noschese, V. Tsamis, K. Tigani, P. Barroy, M. Irzyk, D. Neel, J. P. Godard, D. Lanoiselée, P. Sogorb, D. Verilhac, M. Bretton, F. Signoret, F. Ciabattari, R. Naves, M. Boutet, J. De Queiroz, P. Lindner, K. Lindner, P. Enskonatus, G. Dangl, T. Tordai, H. Eichler, J. Hattenbach, C. Peterson, L. Molnár, R. R. Howell

Abstract
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.

Keywords
methods: observational / methods: data analysis / planets and satellites: atmospheres / techniques: photometric / planets and satellites: physical evolution / planets and satellites: terrestrial planets

Notes
Partly based on observations made with the Ultracam camera at the Very Large Telescope (VLT Paranal), under program ID 079.C-0345(F), the ESO camera NACO at VLT, under program IDs 079.C-0345(B), 089.C-0314(C) and 291.C- 5016, the ESO camera ISAAC at VLT under program ID 085.C-0225(A), the ESO camera SOFI at NTT Paranal, under program ID 085.C-0225(B), the WFI camera at 2.2m La Silla, under program ID's 079.A-9202(A), 075.C-0154, 077.C-0283, 079.C-0345, 088.C-0434(A), 089.C-0356(A), 090.C-0118(A) and 091.C-0454(A), the Laboratório Nacional de Astrofísica (LNA), Itajubá – MG, Brazil, the Southern Astrophysical Research (SOAR) telescope, and the Italian Telescopio Nazionale Galileo (TNG).

Astronomy and Astrophysics
Volume 625, Article Number A42, Number of pages 21
2019 May

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia