Comparison of neutral outgassing of comet 67P/Churyumov-Gerasimenko inbound and outbound beyond 3 AU from ROSINA/DFMS

¹ Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA
² Physikalisches Institut, University of Bern, Sidlerstr. 5, 3012 Bern, Switzerland
³ Center for Space and Habitability (CSH), Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
⁴ Laboratoire Atmosphères, Milieux, Observations Spatiales, Institut Pierre Simon Laplace, CNRS, Université Pierre et Marie Curie, 4 avenue de Neptune, 94100 Saint-Maur, France
⁵ Department of Physics/SPAT, Imperial College London, London SW7 2AZ, UK
⁶ Belgian Institute for Space Aeronomy, BIRA-IASB, Ringlaan 3, 1180 Brussels, Belgium
⁷ Center for Plasma Astrophysics, K.U. Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium
⁸ Institute of Computer and Network Engineering (IDA), TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig, Germany
⁹ Space Science Directorate, Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78228, USA
e-mail: sfuselier@swri.edu
¹⁰ Department of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward, Ann Arbor, MI 48109, USA
¹¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
¹² Laboratoire d’Astrophysique de Marseille, CNRS, Aix Marseille Université, 13388 Marseille, France
¹³ Lockheed Martin Space Systems Advanced Technology Center, 3251 Hanover St., Palo Alto, CA 94304, USA
¹⁴ Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, 3665 Discovery Dr., Boulder, CO 80309, USA

Received: 30 May 2018
Accepted: 26 January 2019

Abstract

Context. Pre-equinox measurements of comet 67P/Churyumov-Gerasimenko with the mass spectrometer ROSINA/DFMS on board the Rosetta spacecraft revealed a strongly heterogeneous coma. The abundances of major and various minor volatile species were found to depend on the latitude and longitude of the nadir point of the spacecraft. The observed time variability of coma species remained consistent for about three months up to equinox. The chemical variability could be generally interpreted in terms of surface temperature and seasonal effects superposed on some kind of chemical heterogeneity of the nucleus.

Aims. We compare here pre-equinox (inbound) ROSINA/DFMS measurements from 2014 to measurements taken after the outbound equinox in 2016, both at heliocentric distances larger than 3 AU. For a direct comparison we limit our observations to the southern hemisphere.

Methods. We report the similarities and differences in the concentrations and time variability of neutral species under similar insolation conditions (heliocentric distance and season) pre- and post-equinox, and interpret them in light of the previously published observations. In addition, we extend both the pre- and post-equinox analysis by comparing species concentrations with a mixture of CO₂ and H₂O.

Results. Our results show significant changes in the abundances of neutral species in the coma from pre- to post-equinox that are indicative of seasonally driven nucleus heterogeneity.

Conclusions. The observed pre- and post-equinox patterns can generally be explained by the strong erosion in the southern hemisphere that moves volatile-rich layers near the surface.