Constraints on the structure and seasonal variations of Triton’s atmosphere from the 5 October 2017 stellar occultation and previous observations^*

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 5 place Jules Janssen, 92190 Meudon, France
² UNESP - São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, Guaratinguetá, SP 12516-410, Brazil
³ Laboratório Interinstitucional de e-Astronomia - LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
⁴ Instituto de Astrofísica de Andalucía (IAA-CSIC). Glorieta de la Astronomía s/n. 18008- Granada, Spain
⁵ Departments of Earth & Planetary Sciences and Physics & Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁶ National Aeronautics and Space Administration (NASA), Ames Research Center, Space Science Division, Moffett Field, CA 94035, USA
⁷ Laboratoire de Météorologie Dynamique, IPSL, Université PSL, CNRS, Sorbonne Université, 4 place Jussieu, 5005 Paris, France
⁸ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
⁹ IMCCE/Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Lille - Avenue Denfert Rochereau, 5014 Paris, France
¹⁰ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
¹¹ Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile
¹² Comisión Nacional de Investigatión y Desarrollo Aeroespacial del Perú - CONIDA, Peru
¹³ Observatorio Astronómico de Moquegua, Moquegua, Peru
¹⁴ naXys, University of Namur, 8 Rempart de la Vierge, Namur 5000, Belgium
¹⁵ Florida Space Institute, University of Central Florida, 12354 Research Parkway, Partnership 1, Orlando, FL, USA
¹⁶ Federal University of Technology-Paraná (UTFPR / DAFIS), Curitiba, Brazil
¹⁷ Observatório Nacional/MCTIC, Rio de Janeiro, Brazil
¹⁸ Universidade Federal do Rio de Janeiro - Observatório do Valongo, Ladeira Pedro Antônio 43, CEP 20.080-090 Rio de Janeiro - RJ, Brazil
¹⁹ Polo Educacional Sesc, Av. Ayrton Senna, 56, Jacarepaguá, Rio de Janeiro CEP 22 5-004, Brazil
²⁰ Université de Lille, Observatoire de Lille, 1, impasse de l’Observatoire, 59000 Lille, France
²¹ Dpto. Física Aplicada, Escuela de Ingeniería de Bilbao, Universidad del País Vasco (UPV/EHU), Plaza Ingeniero Torres Quevedo 1, 48013, Bilbao, Spain
²² Internationale Amateursternwarte (IAS) e. V., Mittelstr. 6, 15749 Mittenwalde, Germany
²³ International Occultation Timing Association - European Section (IOTA/ES), Am Brombeerhag 13, 30459 Hannover, Germany
²⁴ Trans-Tasman Occultation Alliance (TTOA) PO Box 2241, Wellington, New Zealand
²⁵ International Occultation Timing Association (IOTA), PO Box 152, Kent, WA 98042, USA
²⁶ Vereinigung der Sternfreunde e.V. (VdS), Heppenheim an der Bergstrasse, Germany
²⁷ Saint-Sulpice Observatory, Club Eclipse, Thierry Midavaine, 102 rue de Vaugirard, 75006 Paris, France
²⁸ Dutch Occultation Association/Dutch observers of Asteroids (DOA), The Netherlands
²⁹ Archenhold Sternwarte, Alt-Treptow 1, 12435 Berlin, Germany
³⁰ British Astronomical Association, Burlington House, Piccadilly, London, W1J 0DU, UK
³¹ European Space Agency ESA, ESTEC SCI-S, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³² Section of Astrophysics, Astronomy and Mechanics, Department of Physics, National and Kapodistrian University of Athens, 15784 Zografos, Athens, Greece
³³ Hellenic Amateur Astronomy Association, Athens, Greece
³⁴ Armagh Observatory and Planetarium, Northern Ireland, UK
³⁵ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, P. Penteli, 15236 Athens, Greece
³⁶ Department of Physics, University of Crete, 71003 Heraklion, Greece
³⁷ Institute of Astrophysics, Foundation for Research and Technology-Hellas, 70013 Heraklion, Greece
³⁸ Astronomical Institute of the Czech Academy of Sciences, Fricova 298, 25165 Ondřejov, Czech Republic
³⁹ Sternwarte Stuttgart, Stuttgart, Germany
⁴⁰ Hieronymusstr. 15b, 81241 Munich/München, Germany
⁴¹ Astronomische Arbeitsgemeinschaft Wanne-Eickel / Herne e.V., Breitenweg, Germany
⁴² Observatory: Sternwarte Zollern-Alb, Rosenfeld-Brittheim e.V., Germany
⁴³ AVV (Astronomische Vereinigung Vulkaneifel) Astronomical Society Volcano Eifel, Schalkenmehren, Germany
⁴⁴ Department of Physics, Ariel University, Ariel 40700, Israel
⁴⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴⁶ Selztal Observatory, Friesenheim, Bechtolsheimer, Germany
⁴⁷ Bochumer Herbsttagung der Amateuratsronomen (BoHeTa), Germany
⁴⁸ Gesellschaft für volkstümliche Astronomie e.V. Hamburg, Hammerichstraße 5, 22605 Hamburg, Germany
⁴⁹ Gruppo Astrofili Massesi, EURASTER, Massa, Italy
⁵⁰ Astronomical Observatory of the Autonomous Region of the Aosta Valley, Nus (AO) 11020, Italy
⁵¹ Mount Agliale Observatory, Galileo Park, Vinewood Hills, Germany
⁵² AAB - Associazione Astrofili Bolognesi, Bologna, Italy
⁵³ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁵⁴ via Radicosa 44, 80051 Agerola, Italy
⁵⁵ Associazione Astrofili Aurunca, 1, Via Giordano Bruno - 81037 Sessa Aurunca, Italy
⁵⁶ Astrocampania Associazione - Osservatorio Salvatore di Giacomo - Agerola (NA) - Italy
⁵⁷ Gruppo Astrofili Catanesi, via Milo 28, 95125 Catania, Italy
⁵⁸ Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, 95123 Catania, Italy
⁵⁹ Astronomical Society of Tunisia, Tunisia
⁶⁰ Société Astronomique de Genève, Genève, Switzerland
⁶¹ Observatoire de Genève, 1290 Sauverny, Switzerland
⁶² AstroVal, Observatoire de la Vallée de Joux, 1347 Le Solliat, Switzerland
⁶³ Observatoire François-Xavier Bagnoud, 3961 St-Luc, Switzerland
⁶⁴ Société Neuchâteloise d’Astronomie, Genève, Switzerland
⁶⁵ Department of Physics, ETH Zurich, Wolfgang-Pauli-strasse 27, 8093 Zurich, Switzerland
⁶⁶ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-strasse 27, 8093 Zurich, Switzerland
⁶⁷ 6525 Gnosca, Switzerland
⁶⁸ Meekrap-oord 3, 3991 VE Houten, The Netherlands
⁶⁹ Observatoire Centre-Ardenne, 6840 Grapfontaine, Belgium
⁷⁰ ADAGIO, Belesta observatory (A05: MPC code), Belesta en Lauragais 31 - France
⁷¹ 13200 Arles, France
⁷² Observatoire les Pléiades, Latrape, France
⁷³ Observatoire des Baronnies Provençales, 05150 Moydans, France
⁷⁴ Association Photographie Astronomie Montredonnaise (APAM), France
⁷⁵ 75000 Paris, France
⁷⁶ Observatoire de la Côte d’Azur (OCA), Boulevard de l’Observatoire, Nice, France
⁷⁷ Ciel et Espace, 63-65 boulevard Massena, 75013 Paris, France
⁷⁸ 78180 Montigny le Bretonneux, France
⁷⁹ Albireo78 Association, Yvelines, France
⁸⁰ Sadr Association, Yvelines, France
⁸¹ Société Astronomique de France, Paris, France
⁸² Instituto de Astrofísica e Ciências do Espaço (IA), Universidade de Lisboa, Tapada da Ajuda - Edifício Leste - 2° Piso 1349-018 Lisboa, Portugal
⁸³ Euraster, 1 rue du Tonnelier, 46100 Faycelles, France
⁸⁴ 77350 Le Mée-sur-Seine, France
⁸⁵ Airylab, 04800 Greoux les Bains, France
⁸⁶ Observatoire des Côtes-de-Meuse, 8 Place de Verdun, 55210 Viéville-sous-les-Côtes, France
⁸⁷ Observatoire Midi-Pyrénées et Université Toulouse-III, IRAP, 31400 Toulouse, France
⁸⁸ Observatoire de Saint-Caprais, 81800 Rabastens, France
⁸⁹ Institut Supérieur de l’Aéronautique et de l’Espace, ISAE-SUPAERO, Toulouse University, Toulouse, France
⁹⁰ Université Toulouse-III, FSI, 31400 Toulouse, France
⁹¹ Centre d’Astronomie, 04870 Saint-Michel-l’Observatoire, France
⁹² 93 Société Lorraine d’Astronomie, Vandoeuvre-lès-Nancy, France
⁹³ Uranoscope de l’Ile de France, Gretz Armainvilliers, UAI A07, France
⁹⁴ GEOPS – Géosciences Paris Sud, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Orsay, France
⁹⁵ Association Marseillaise d’Astronomie (AMAS), Marseille, France
⁹⁶ O.A.B.A.C. – Observatoire Astronomique du Beausset André Coliac, Beausset, France
⁹⁷ Astroclub Urania 31, Cugnaux, France
⁹⁸ 28800 Sancheville, France
⁹⁹ Observatoire de Puimichel, 04700 Puimichel, France
¹⁰⁰ Observatoire Charles Fehrenbach, Prisches, France
¹⁰¹ Astro Club de France, Prisches, France
¹⁰² 22540 Louargat, France
¹⁰³ Université Grenoble Alpes, Inria, 38000 Grenoble, France
¹⁰⁴ Université Paris-Saclay, Université Paris-Sud, 91400 Orsay, France
¹⁰⁵ SAS Les Pleiades (Opticiens), Perigueux, France
¹⁰⁶ LOMA CNRS-Université de Bordeaux UMR5798, France
¹⁰⁷ Vendéen Astronomical Center, Vendée, France
¹⁰⁸ Association Dinastro, Visker, France
¹⁰⁹ Center of Research in Astronomy, Astrophysics and Geophysics (CRAAG) - Algiers Observatory, Algeria
¹¹⁰ Hampshire Astronomical Group, Clanfield, UK
¹¹¹ Royal Astronomical Society, Burlington House, Piccadilly, London W1J 0BQ, UK
¹¹² American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138, USA
¹¹³ UCL Observatory, Dept. of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK
¹¹⁴ CR2 9BF, UK
¹¹⁵ Reading Astronomical Society, Earley, Reading RG6 1EY, UK
¹¹⁶ Dept. of Software Engineering, University of Granada, Spain
¹¹⁷ SAG, Sociedad Astronómica de Granada, Spain
¹¹⁸ Puckett Observatory, PO BOX 818 Ellijay, Ga. 30540 USA
¹¹⁹ Centro de Estudios de Física del Cosmos de Aragón, Plaza San Juan 1, 44001 Teruel, Spain
¹²⁰ Astrophysics Department, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
¹²¹ Observatorio de Forcarei, Forcarei, Pontevedra, Spain
¹²² Observatorio Astronómico de Albox - C/ Poeta Martin Torregrosa no8 2°A - 04800 Albox - Almeria, Spain
¹²³ Liverpool Telescope Group, Astrophysics Research Institute, Liverpool John Moores University, UK
¹²⁴ Observatorio Astronómico de Guirguillano, Navarra, Spain
¹²⁵ Observatorio Astronómico La Hita, 45850 La Villa de Don Fadrique, Toledo, Spain
¹²⁶ Observatorio Astronómico, Universidad de Valencia, Valencia, Spain
¹²⁷ Agrupacio Astronomica de Sabadell, Occultation’s Group, C/. Prat de la Riba, s/n., 0/8203, Sabadell, Barcelona, Spain
¹²⁸ Astrophysics department, CEA/DRF/IRFU/DAp, Université Paris Saclay, UMR AIM, 91191 Gif-sur-Yvette, France
¹²⁹ Institut de Ciències del Espai, Campus UAB, Carrer de Can Magrans, s/n, 08193, Barcelona, Spain
¹³⁰ Instituto Politécnico de Tomar, CI2 e U.D. Matemática e Física, Portugal
¹³¹ Observatório Astronómico, Centro Ciência Viva de Constância, Portugal
¹³² Centro Ciência Viva do Algarve, Faro, Portugal
¹³³ Fundamental and Applied Physics Laboratory - Safi, Physics Department, Polydisciplinary Faculty, Safi, Cadi Ayyad University, Morocco
¹³⁴ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, FSSM, Cadi Ayyad University, Marrakech, Morocco
¹³⁵ Astrobiology Research Unit, Université de Liège, 19C Allée du 6 Août, 4000 Liège, Belgium
¹³⁶ Laboratory of High Energy Physics and Astrophysics, Physics department, Cadi Ayad University, PB 2390, Marrakech 40000, Morocco
¹³⁷ STAR Institute, Université de Liège, Allée du 6 août, 19C, 4000 Liège, Belgium
¹³⁸ 68490 Ottmarsheim, France
¹³⁹ Department of Astronomy and Carl Sagan Institute, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA
¹⁴⁰ Cornell Center for Astrophysics and Planetary Science, Carl Sagan Institute, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA
¹⁴¹ Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
¹⁴² Department of Physics and Astronomy, Appalachian State University, Boone, North Carolina, USA
¹⁴³ Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina, USA
¹⁴⁴ Central (Pulkovo) Observatory of the Russian Academy of Sciences, 196140, 65/1 Pulkovskoye Ave., Saint Petersburg, Russia
¹⁴⁵ 78 rue de la tombe Issoire, 75014 Paris, France
¹⁴⁶ Association de Gestion de l’Observatoire Réunionais d’Astronomie (AGORA), Observatoire des Makes, La Réunion Island, France
¹⁴⁷ Association Réunionnaise pour l’Etude du Ciel Austral (ARECA), La Réunion Island, France
¹⁴⁸ Planétarium de Vaulx-en-Velin, Place de la Nation, 69120 Vaulx-en-Velin, France
¹⁴⁹ Association AT60, Observatoire du Pic du Midi, France
¹⁵⁰ Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
¹⁵¹ Reitsema Enterprises Inc, 1584 Waukazoo Drive Holland, MI 49424, USA
¹⁵² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁵³ Astronomical Association of Queensland, St. Lucia, Queensland, Australia
¹⁵⁴ Bundaberg Astronomical Society Inc., Bundaberg, Australia
¹⁵⁵ Brisbane Astronomical Society, Australia

Received: 31 May 2021
Accepted: 17 November 2021

Abstract

Context. A stellar occultation by Neptune’s main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection.

Aims. We aimed at constraining Triton’s atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis.

Methods. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range ~8 km to ~190 km, corresponding to pressure levels from 9 µbar down to a few nanobars.

Results. (i) A pressure of 1.18 ± 0.03 µbar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 µbar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude.