Compressive strength of comet 67P/Churyumov-Gerasimenko derived from Philae surface contacts

Heinisch, Philip; Auster, H. U.; Gundlach, Bastian; Blum, Jürgen; Güttler, C.; Tubiana, C.; Sierks, H.; Hilchenbach, M.; Biele, Jens; Richter, Ingo; Glaßmeier, Karl‐Heinz

doi:10.1051/0004-6361/201833889

Cited by 21 publications

(11 citation statements)

References 45 publications

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“…As previously indicated, the tensile strength of comet 67P/C-G is consistent with the hierarchical aggregate model proposed by Skorov & Blum (2012). The compressive strength of the surface material of the comet can also be reproduced by the hierarchical aggregate model (see Heinisch et al 2019). Therefore, the gravitational collapse of a concentrated clump of pebbles in the solar nebula is the best model that explains the formation process of comets.…”

Section: Introductionsupporting

confidence: 86%

Thermal inertias of pebble-pile comet 67P/Churyumov–Gerasimenko

Arakawa

Ohno

2020

Monthly Notices of the Royal Astronomical Society

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Abstract The Rosetta mission to comet 67P/Churyumov–Gerasimenko has provided new data to better understand what comets are made of. The weak tensile strength of the cometary surface materials suggests that the comet is a hierarchical dust aggregate formed through gravitational collapse of a bound clump of small dust aggregates so-called “pebbles” in the gaseous solar nebula. Since pebbles are the building blocks of comets, which are the survivors of planetesimals in the solar nebula, estimating the size of pebbles using a combination of thermal observations and numerical calculations is of great importance to understand the planet formation in the outer solar system. In this study, we calculated the thermal inertias and thermal skin depths of the hierarchical aggregates of pebbles, for both diurnal and orbital variations of the temperature. We found that the thermal inertias of the comet 67P/Churyumov–Gerasimenko are consistent with the hierarchical aggregate of cm- to dm-sized pebbles. Our findings indicate that the icy planetesimals may have formed via accretion of cm- to dm-sized pebbles in the solar nebula.

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Section: Introductionsupporting

confidence: 86%

Thermal inertias of pebble-pile comet 67P/Churyumov–Gerasimenko

Arakawa

Ohno

2020

Monthly Notices of the Royal Astronomical Society

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“…related to shielding effects by the cliffs close to Philae combined with the relatively low level of activity in November 2014. Regarding the compressive strength of Abydos, very different numbers ranging from a few tenths of Pa to 2 MPa were reported in the literature (Spohn et al 2015;Biele et al 2015;Knapmeyer et al 2018;Heinisch et al 2019), although the measurements derived from the penetrator sensors, which give the higher strengths values, should be taken with caution because they are affected by deployment uncertainties.…”

Section: Discussionmentioning

confidence: 94%

Small lobe of comet 67P: Characterization of the Wosret region with ROSETTA-OSIRIS

Fornasier

Micas

Hasselmann

et al. 2021

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Aims. We investigated Wosret, a region located on the small lobe of the 67P/Churyumov-Gerasimenko comet subject to strong heating during the perihelion passage. This region includes the two last landing sites of the Philae lander as well as, notably the final one, Abydos, where the lander performed most of its measurements. We study Wosret in order to constrain its compositional properties and its surface evolution. By comparing them with those of other regions, we aim to identify possible differences among the two lobes of the comet. Methods. We analyzed high-resolution images of the Wosret region acquired between 2015 and 2016 by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) on board the Rosetta spacecraft, at a resolution ranging from 2 to 10 m px−1 before and close to perihelion, up to 0.07–0.2 m px−1 in the post-perihelion images. The OSIRIS images were processed with the OSIRIS standard pipeline, then converted into I∕F radiance factors and corrected for the viewing and illumination conditions at each pixel using the Lommel–Seeliger disk function. Spectral slopes were computed in the 535–882 nm range. Results. We observed a few morphological changes in Wosret, related to local dust coating removal with an estimated depth of ~1 m, along with the formation of a cavity measuring 30 m in length and 6.5 m in depth, for a total estimated mass loss of 1.2 × 106 kg. The spectrophotometry of the region is typical of medium-red regions of comet 67P, with spectral slope values of 15–16%/(100 nm) in pre-perihelion data acquired at phase angle 60°. As observed globally for the comet, also Wosret shows spectral slope variations during the orbit linked to the seasonal cycle of water, with colors getting relatively bluer at perihelion. Wosret has a spectral phase reddening of 0.0546 × 10−4 nm−1 deg−1, which is about a factor of 2 lower than what was determined for the nucleus northern hemisphere regions, possibly indicating a reduced surface micro-roughness due to the lack of widespread dust coating. A few tiny bright spots are observed and we estimate a local water-ice enrichment up to 60% in one of them. Morphological features such as “goosebumps” or clods are widely present and larger in size than similar features located in the big lobe. Conclusions. Compared to Anhur and Khonsu, two southern hemisphere regions in the big lobe which have been observed under similar conditions and also exposed to high insolation during perihelion, Wosret exhibits fewer exposed volatiles and less morphological variations due to activity events. Considering that the high erosion rate in Wosret unveils part of the inner layers of the small lobe, our analysis indicates that the small lobe has different physical and mechanical properties than the big one and a lower volatile content, at least in its uppermost layers. These results support the hypothesis that comet 67P originated from the merging of two distinct bodies in the early Solar System.

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“…The production of a new Philae landing trajectory (Supplementary Methods, Supplementary Fig. 1) served to start the search for TD2, with a ridge region identified as being a likely candidate for its https://doi.org/10.1038/s41586-020-2834-3 location 11 . A comparative analysis was performed of this area using pre-and post-landing imagery ( Supplementary Figs.…”

Section: +02mentioning

confidence: 99%

“…Whereas compressive strengths 1,2 of 1 kPa and 2 MPa were measured at TD1 and TD3 respectively (although deployment uncertainties do affect the reliability of the MUPUS-Multi Purpose Sensors for Surface and Subsurface Science-penetrator result), a number of other publications find much lower values. Model-dependent analyses of the collapse of cliff overhangs observed from orbit 23 , as well as those derived from the scratches Philae made at the final landing location 11 , calculated compressive strength values ranging between 30 Pa and 150 Pa for the former and from 10 Pa to 100 Pa for the latter. Such model-based low compressive strength derivations show consistency with our in situ findings.…”

Section: +02mentioning

confidence: 99%