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

E Meza ,M Ait Moulay Larbi ,O Klös ,Alfonso Noschese ,L Mancini ,J Rovira ,Youssef Moulane ,D Herald ,Anthony Roman ,K Guhl ,M Bretton ,A Selva ,Riccardo Papini ,J Haislip ,N Morales ,Maxime Devogèle ,L Di Fabrizio ,Brian Loader ,P M Kilmartin ,A Maury ,M Gillon ,S Kaspi ,R Duffárd ,William H Allen ,Martina Harnisch ,K Tigani ,W Beisker ,Jean‐Pierre Rivet ,Cyrielle Opitom ,K M Hill ,D Lanoiselée ,L H Wasserman ,A A Cole ,A Magazzù ,Sander Devisscher ,R Vieira-Martins ,John Talbot ,Jean Manfroid ,A B Giles ,A Daassou ,P Barroy ,K.-L Bath ,D Vernet ,E F Young ,A R Gomes-Júnior ,Sergio Alonso ,F Vachier ,K Gazeas ,S Kerr ,Federica Bianco ,T Janik ,Mike Kretlow ,J Marques Oliveira ,D Gloistein ,M Lavayssière ,Rolf A Jansen ,Eric Frappa ,M Jelínek ,P Sogorb ,S Renner ,K Walzel ,François Colas ,M Irzyk ,C Perelló ,B Kattentidt ,Delphine Néel ,J Lecacheux ,L Molnár ,A Lacluyzé ,J.-E Communal ,Frédéric Jabet ,Christian Veillet ,Tanguy Bertrand ,V Lorenzi ,R Cunniffe ,L Tzouganatos ,S P Littlefair ,R Zanmar Sánchez ,C B Olkin ,A Castro Tirado ,B Gährken ,F Braga-Ribas ,Tamás Tordai ,J P Godard ,Greg Bolt ,M Boutet ,J Broughton ,A Dias-Oliveira ,D Gault ,G Wortmann ,G Mckay ,O Faragó ,B Lade ,D Vérilhac ,J L Ortiz ,Alessandro Marchini ,E Molinari ,P B Graham ,Z Benkhaldoun ,A Carbognani ,Noah Brosch ,M Assafin ,Alison Pennell ,R Behrend ,F Forget ,T R Marsh ,V S Dhillon ,Emmanuël Jehin ,Diane Bérard ,Franck Marchis ,H Eichler ,P Bendjoya ,A Doressoundiram ,L A Young ,J T Pollock ,I Manulis ,S Parker ,G Leto ,Stephen Todd ,Y El Azhari ,D E Reichart ,A Eberle ,P Santos-Sanz ,H Pavlov ,Jan Hattenbach ,G Krannich ,David Polishook ,P Enskonatus ,B Sicardy ,M Conti ,F Signoret ,K Lindner ,Zdeněk Moravec ,B E Morgado ,M W Buie ,Jo Milner ,J I B Camargo ,J Ohlert ,D Hampf ,G Murawsky ,R G French ,G Bonnoli ,T Dobosz ,V Tsamis ,L Abe ,P Lindner ,R Naves ,G Dangl ,W Rothe ,J Greenhill ,R Gil-Hutton ,F Roques ,K Ivarsen ,Harald Bode ,Fabio Salvaggio ,F Ciabattari ,A C Gilmore ,Thomas Widemann ,G Benedetti-Rossi ,J Desmars ,Richard Querel ,V D Ivanov ,J De Queiroz ,Jocelyn Sérot ,Caitlin A Peterson ,Rodrigo Leiva ,Pedro Machado ,M Dohrmann ,E Lellouch ,R R Howell

doi:10.1051/0004-6361/201834281

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.

Highlights

IntroductionEarth-based stellar occultations have been a highly efficient method to study the atmosphere of Pluto
The tenuous atmosphere of Pluto was glimpsed during a groundbased stellar occultation observed on 1985 August 19 (Brosch 1995), and fully confirmed on 1988 June 9 during another occultation (Hubbard et al 1988; Elliot et al 1989; Millis et al 1993) that provided the main features of its structure: temperature, composition, pressure, and density; see the review by Yelle & Elliot (1997).Since Earth-based stellar occultations have been a highly efficient method to study the atmosphere of Pluto
As Pluto moved in front of the Galactic center, the yearly rate of stellar occultations dramatically increased during the 2002–2016 period, yielding a few events per year that greatly improved our knowledge of the atmospheric structure and evolution of this planet

Summary

Introduction

Earth-based stellar occultations have been a highly efficient method to study the atmosphere of Pluto. They yield, in the best cases, information from a few kilometers above the surface (pressure ∼10 μbar) up to 380 km in altitude (∼10 nbar). As Pluto moved in front of the Galactic center, the yearly rate of stellar occultations dramatically increased during the 2002–2016 period, yielding a few events per year that greatly improved our knowledge of the atmospheric structure and evolution of this planet. The subsolar latitude has gone from 0◦ at equinox to 54◦ north in July 2016 In this context, dramatic seasonal effects are expected, and observed

Objectives

Findings

Conclusion