Volume 630, October 2019
Rosetta mission full comet phase results
|Number of page(s)||16|
|Section||Planets and planetary systems|
|Published online||20 September 2019|
Analysis of night-side dust activity on comet 67P observed by VIRTIS-M: a new method to constrain the thermal inertia on the surface
Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome, Italy
2 Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
3 Institute of Planetary Research, DLR, 12489 Berlin, Germany
4 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
5 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
6 Università degli Studi di Napoli Parthenope, Dip. di Scienze e Tecnologie, CDN IC4, 80143 Naples, Italy
7 Department of Physics and Astronomy, University of Padova, Via Marzolo 8, 35131 Padova, Italy
8 Department of Physics, Oxford University, Oxford, UK
9 INAF – Osservatorio Astrofisico di Arcetri, Firenze, Italy
10 ASI, Via del Politecnico snc, 00133, Rome, Italy
Accepted: 28 March 2019
On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25–36 W K−1 m−2 s−1/2. These thermal inertia values can be used to verify with a 3D finite-element method (FEM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m−2 K−1 s−0.5; (2) the same structure, but with thermal inertia of 100 J m−2 K−1 s−0.5; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 ± 4.8%/100 nm to 13 ± 2.6%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between −2.5 and −3.
Key words: comets: general / comets: individual: 67P/Churyumov-Gerasimenko / infrared: planetary systems
© ESO 2019
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