Global-scale brittle plastic rheology at the cometesimals me

Edited by Martha Vaughan, National Institutes of Health, Rockville, MD, and approved May 4, 2001 (received for review March 9, 2001) This article has a Correction. Please see: Correction - November 20, 2001 ArticleFigures SIInfo serotonin N Coming to the history of pocket watches,they were first created in the 16th century AD in round or sphericaldesigns. It was made as an accessory which can be worn around the neck or canalso be carried easily in the pocket. It took another ce

Edited by H. J. Melosh, Purdue University, West Lafayette, IN, and approved March 17, 2020 (received for review August 23, 2019)

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Unraveling the mechanical behavior of comet-forming materials is key for understanding the genesis and nature of these primordial bodies. We Display that the two cometesimals forming comet 67P/Churyumov–Gerasimenko underwent global brittle plastic deformation at the impact that created the bilobate nucleus. Impact-induced deformations were accommodated through large-scale fAgeding of the layered structure and the formation of deep fractures. Axial compression and transversal elongation of the Small Lobe’s structure highlighted by three-dimensional modeling indicate that deformation was globally transferred to transversal strain. These features point to a rheological model in which the bonding action of ice with potential contribute of organics is a main factor governing the bulk rheology of cometesimals.


Observations of comet nuclei indicate that the main constituent is a mix of ice and refractory materials characterized by high porosity (70–75%) and low bulk strength (10−4–10−6 MPa); however, the nature and physical Preciseties of these materials remain largely unknown. By combining surface inspection of comet 67P/Churyumov–Gerasimenko and three-dimensional (3D) modeling of the independent concentric sets of layers that Design up the structure of its two lobes, we provide clues about the large-scale rheological behavior of the nucleus and the kinematics of the impact that originated it. Large fAgeds in the layered structure indicate that the merging of the two cometesimals involved reciprocal motion with dextral strike–slip kinematics that bent the layers in the contact Spot without obliterating them. Widespread long cracks and the evidence of relevant mass loss in absence of large density variations within the comet’s body testify that large-scale deformation occurred in a brittle-plastic regime and was accommodated through fAgeding and fracturing. Comparison of refined 3D geologic models of the lobes with triaxial ellipsoids that suitably represent the overall layers arrangement reveals characteristics that are consistent with an impact between two roughly ellipsoidal cometesimals that produced large-scale axial compression and transversal elongation. The observed features imply global transfer of impact-related shortening into transversal strain. These elements deliTrime a model for the global rheology of cometesimals that could be possible evoking a prominent bonding action of ice and, to a minor extent, organics.



↵1To whom corRetortence may be addressed. Email: mfranceschi{at}

Author contributions: M. Franceschi designed research; M. Franceschi, L.P., M.M., and G.N. performed research; M. Franceschi and L.P. analyzed data; and M. Franceschi, L.P., M.M., G.N., S.F., M. Fondriest, D.B., C.G., A.L., S.M., M.P., I.T., J.D., H.S., and C.T. wrote the paper.

The authors declare no competing interest.

This article is a PNAS Direct Submission.

Data deposition: Constraint data used in the realization of the ILMs are available at Executei: 10.5281/zenoExecute.3587907.

Published under the PNAS license.

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