Sunset jets observed on comet 67P/Churyumov-Gerasimenko sustained by subsurface thermal lag

¹ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
e-mail: shi@mps.mpg.de
² Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
³ Institut für Geophysik und extraterrestrische Physik (IGEP), Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
⁴ Physikalisches Institut der Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland
⁵ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstraße 2, 12489 Berlin, Germany
⁶ Centro di Ateneo di Studi ed Attivitá Spaziali “Giuseppe Colombo” (CISAS), University of Padova, via Venezia 15, 35131 Padova, Italy
⁷ LESIA-Observatoire de Paris, CNRS, Université Pierre et Marie Curie, Université Paris Diderot, 5 place J. Janssen, 92195 Meudon, France
⁸ Graduate Institute of Astronomy, National Central University, 300 Chung-Da Rd, 32054 Chung-Li, Taiwan
⁹ Department of Physics and Astronomy “G. Galilei”, University of Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹⁰ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astro-physique de Marseille) UMR 7326, 13388 Marseille, France
¹¹ Centro de Astrobiología (CSIC-INTA), 28850 Torrejón de Ardoz, Madrid, Spain
¹² International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
¹³ Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 Noordwijk, The Netherlands
¹⁴ PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
¹⁵ LATMOS, CNRS/UVSQ/IPSL, 11 Boulevard d’Alembert, 78280 Guyancourt, France
¹⁶ INAF Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁷ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁸ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁹ Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy
²⁰ University of Trento, via Sommarive 9, 38123 Trento, Italy
²¹ INAF Osservatorio Astronomico di Trieste, via Tiepolo 11, 34014 Trieste, Italy
²² Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomia, 18008 Granada, Spain
²³ Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Cañada ( Madrid), Spain
²⁴ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy

Received: 5 August 2015
Accepted: 5 December 2015

Abstract

We present observations of sunset jets on comet 67P/Churyumov-Gerasimenko by Rosetta/OSIRIS camera. In late April 2015, when the comet was at a heliocentric distance of ~1.8 AU, clusters of dust jets that originated in the Ma’at region on the comet’s small lobe were identified from multipleimages and were apparently sustained for about an hour beyond local sunset. Emanating from the shadowed nucleus, these jets became visible by solar illumination at their apparent sources up to only a few tens of meters above the nucleus surface. We investigate the plausibility of these jets as having been triggered by water ice sublimation and sustained by thermal lag in the subsurface beyond sunset. A general thermo-physical model was parameterized such that the thermal lag in the subsurface is consistent with the elapsed time of observation after sunset. It is found that the sublimation of water ice from a depth of 6 mm and with a low thermal inertia of 50 W m^-2 K^-1 s^1/2 could explain the spatial pattern and evolution of the apparent sources, particularly their disappearance due to the eventual cooling of the subsurface. Our analysis suggests that these sunset jets were essentially day-side dust activities that continued after sunset. Specific observational conditions for the sunset jets constrain their possible sources to mostly within the less abrupt, dusty terrains. The uneven distribution of these jets is possibly related to subsurface inhomogeneities in the dusty area.