Comets and Asteroids

Cliff Collapse On Comet 67P/Churyumov-Gerasimenko – I. Aswan

By Keith Cowing
Status Report
November 25, 2023
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Cliff Collapse On Comet 67P/Churyumov-Gerasimenko – I. Aswan
Left: This image shows an oblique view of the Aswan collapse site. Five months after the collapse it clearly stands out as a substantially brighter region. The normal albedo is 0.17 ± 0.01 (Pajola et al. 2017a) and the current modelling suggests that dust and water ice near the intrinsic nucleus mixing ratio was exposed at this time (but no CO2 ice). Image MTP024 / n20151226t170504370id4df22.img (Sierks & the OSIRIS Team 2018b) was acquired on 2015 December 26 with ∼ 1.4 m px−1 resolution when Rosetta was 77.0 km from the comet. Right: This is a face–on view of the cliff showing that the brightness of the scar is significantly reduced, yet somewhat higher than for the surroundings eleven months after collapse. At this point the current modelling suggests a ∼ 0.5 mm dust mantle, i. e., so thin that some reflection of the water ice still might reach the surface. Image MTP030 / n20160608t143426745id4df22.img (Sierks & the OSIRIS Team 2018c) was acquired on 2016 June 8 with ∼ 0.5 m px−1 resolution when Rosetta was 29.7 km from the comet. — astro-ph.EP

The Aswan cliff on Comet 67P/Churyumov-Gerasimenko collapsed on 2015 July 10. Thereby, relatively pristine comet material from a depth of ~12 m was exposed at the surface. Observations of the collapse site by the microwave instrument Rosetta/MIRO have been retrieved from 8 months prior to collapse, as well as from 5, 7, and 11 months post-collapse.

The MIRO data are analysed with thermophysical and radiative transfer models. The pre-collapse observations are consistent with a 30 MKS thermal inertia dust mantle with a thickness of at least 3 cm.

The post-collapse data are consistent with:

1) a dust/water-ice mass ratio of 0.9±0.5 and a molar CO2 abundance of ~30 per cent relative to water;
2) formation of a dust mantle after ~7 months, having a thickness of a few millimetres or a fraction thereof;
3) a CO2 ice sublimation front at 0.4 cm that withdrew to 2.0 cm and later to 20±6 cm;
4) a thermal inertia ranging 10-45 MKS;
5) a gas diffusivity that decreased from 0.1m2s−1 to 0.001m2s−1;
6) presence of a solid-state greenhouse effect parts of the time.

The data and the analysis provide a first empirical glimpse of how ice-rich cometary material ages and evolves when exposed to solar heating.

Björn J. R. Davidsson

Comments: 22 pages, 24 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2311.11158 [astro-ph.EP] (or arXiv:2311.11158v1 [astro-ph.EP] for this version)
Journal reference: Mon. Not. R. Astron. Soc. 527, 112-133 (2024)
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Submission history
From: Björn Davidsson
[v1] Sat, 18 Nov 2023 20:19:36 UTC (1,874 KB)
Astrobiology, Astrochemistry, Astrogeology,

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