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

Xian Shi (1) , Xuan Hu (1) , Holger Sierks (1) , Carsten Güttler (1) , Michael A’hearn (2) , Jürgen Blum (3) , Mohamed Ramy El-Maarry (4) , Ekkehard Kührt (5) , Stefano Mottola (5) , Maurizio Pajola (6) , Nilda Oklay (1) , Sonia Fornasier (7) , Cécilia Tubiana (1) , Horst Uwe Keller (3) , Jean-Baptiste Vincent (1) , Dennis Bodewits (2) , Sebastien Höfner (1) , Zhong-Yi Lin (8) , Adeline Gicquel (1) , Marc Hofmann (1) , Cesare Barbieri (9) , Philippe Lamy (10) , Rafael Rodrigo (11, 12) , Detlief Koschny (13) , Hans Rickman (14) , Maria Antonella Barucci (7) , Jean-Loup Bertaux (15) , Ivano Bertini (6) , Gabriele Cremonese (16) , Vania da Deppo (17) , Björn Davidsson (18) , S. Debei (19) , Mariolino de Cecco (20) , Marco Fulle (21) , O. Groussin (10) , Pedro J. Gutiérrez (22) , Stubbe F. Hviid (5) , Wing-H. Ip (8) , Laurent Jorda (10) , Jörg Knollenberg (5) , Gabor Kovacs (1) , Jörg-Rainer Kramm (1) , Michael Küppers (23) , Luisa M. Lara (22) , Monica Lazzarin (9) , José J. Lopez-Moreno (22) , F. Marzari (9) , Giampiero Naletto (24, 6, 17) , Nicolas Thomas (4)

1 MPS - Max-Planck-Institut für Sonnensystemforschung
2 Department of Astronomy [College Park]
3 IGEP - Institut für Geophysik und Extraterrestrische Physik [Braunschweig]
4 Physikalisches Institut [Bern]
5 DLR Institute of Planetary Research
6 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
7 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
8 IANCU - Institute of Astronomy [Taiwan]
9 Dipartimento di Fisica e Astronomia "Galileo Galilei"
10 LAM - Laboratoire d'Astrophysique de Marseille
11 CAB - Centro de Astrobiologia [Madrid]
12 ISSI - International Space Science Institute [Bern]
13 RSSD - Research and Scientific Support Department, ESTEC
14 CBK - Space Research Centre of Polish Academy of Sciences
15 PLANETO - LATMOS
16 OAPD - INAF - Osservatorio Astronomico di Padova
17 IFN - CNR Institute for Photonics and Nanotechnologies
18 Department of Physics and Astronomy [Uppsala]
19 Department of Industrial Engineering [Padova]
20 University of Trento [Trento]
21 OAT - INAF - Osservatorio Astronomico di Trieste
22 IAA - Instituto de Astrofísica de Andalucía
23 Operations Department (ESAC)
24 DEI - Department of Information Engineering [Padova]

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 ~1.8AU, 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 s1/2 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.

Keywords: comets; 67P/Churyumov-Gerasimenko

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]; Earth and Planetary Astrophysics [astro-ph.EP]; Sciences of the Universe [physics]; Astrophysics [astro-ph]; Solar and Stellar Astrophysics [astro-ph.SR]; Sciences of the Universe [physics]; Astrophysics [astro-ph]; Instrumentation and Methods for Astrophysic [astro-ph.IM]

Xian Shi, Xuan Hu, Holger Sierks, Carsten Güttler, Michael A’hearn, et al.. Sunset jets observed on comet 67P/Churyumov-Gerasimenko sustained by subsurface thermal lag. Astronomy and Astrophysics - A&A, 2016, 586, A7 (13 p.). ⟨10.1051/0004-6361/201527123⟩. ⟨insu-01260243⟩