Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta

¹ Max Planck Institute for Solar System Research, Göttingen, Germany
e-mail: tubiana@mps.mpg.de
² Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome, Italy
³ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁴ Institute for Geodesy and Geoinformation Science, Technical University Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
⁵ International Space Science Institute, Bern, Switzerland
⁶ INAF – Osservatorio Astronomico, Trieste, Italy
⁷ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne, Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁸ Department of Physics, Oxford University, Oxford, UK
⁹ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Berlin, Germany
¹⁰ Lunar and Planetary Laboratory, University of Arizona, Tucson, USA
¹¹ Physics Department, Auburn University, Auburn, AL 36849, USA
¹² Laboratoire Atmosphères, Milieux et Observations Spatiales, CNRS & Université de Versailles Saint-Quentin-en-Yvelines, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹³ Centro de Astrobiologia, CSIC-INTA, Torrejon de Ardoz, Madrid, Spain
¹⁴ Science Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands
¹⁵ Jet Propulsion Laboratory, M/S 183-401, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁶ LATMOS, CNRS/UVSQ/IPSL, 11 Boulevard d’Alembert, 78280 Guyancourt, France
¹⁷ Department of Physics and Astronomy “Galileo Galilei”, University of Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹⁸ INAF – Astronomical Observatory of Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁹ CNR-IFN UOS Padova LUXOR, Via Trasea 7, 35131 Padova, Italy
²⁰ Department of Industrial Engineering, University of Padova, Via Venezia 1, 35131 Padova, Italy
²¹ Faculty of Engineering, University of Trento, Via Mesiano 77, 38121 Trento, Italy
²² Instituto de Astrofísica de Andalucía (CSIC), c/ Glorieta de la Astronomia s/n, 18008 Granada, Spain
²³ Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
²⁴ Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
²⁵ University of Padova, Department of Physics and Astronomy “Galileo Galilei”, Via Marzolo 8, 35131 Padova, Italy
²⁶ Graduate Institute of Astronomy, National Central University, 300 Chung-Da Rd, Chung-Li 32054, Taiwan
²⁷ Space Science Institute, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau
²⁸ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
²⁹ Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
³⁰ LATMOS, Sorbonne University, CNRS, UVSQ, Campus Pierre et Marie Curie, BC 102, 4 place Jussieu, 75005 Paris, France
³¹ DIST, Universita Parthenope, Centro Direzionale Isola C4, 80100 Napoli, Italy

Received: 14 December 2018
Accepted: 6 May 2019

Abstract

Context. On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.

Aims. We aim to characterize the spatial distribution of dust, H₂O, and CO₂ gas in the inner coma. To do this, we performed a quantitative analysis of the release of dust and gas and compared the observed H₂O production rate with the rate we calculated using a thermophysical model.

Methods. For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H₂O emission band), and 4200 nm (CO₂ emission band). We measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center.

Results. The spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO₂ is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0° subsolar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO₂ production. An excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270°–50°). A drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50°–90°). Possible explanations of these observations are presented and discussed.