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Low velocity collisions of porous planetesimals in the early solar system

de Niem, Detlef and Hviid, Stubbe and Kührt, Ekkehard and Davidsson, Björn (2018) Low velocity collisions of porous planetesimals in the early solar system. Icarus, 301, pp. 196-218. Elsevier. DOI: 10.1016/j.icarus.2017.09.024 ISSN 0019-1035

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Official URL: https://www.sciencedirect.com/science/article/abs/pii/S0019103516305085

Abstract

The ESA Rosetta mission has shown that Comet 67P/Churuymov–Gerasimenko is bi-lobed, has a high average porosity of around 70%, does not have internal cavities on size scales larger than 10 m, the lobes could have individual sets of onion shell-like layering, and the nucleus surface contains 100 m-scale cylindrical pits. It is currently debated whether these properties are consistent with high-velocity collisional evolution or if they necessarily are surviving signatures of low-velocity primordial accretion. We use an Eulerian hydrocode to study collisions between highly porous bodies of different sizes, material parameters and relative velocities with emphasis on 5–100 m/s to characterize the effects of collisions in terms of deformation, compaction, and heating. We find that accretion of 1 km cometesimals by 3 km nuclei at 13.5 m/s flattens and partially buries the cometesimal with ∼1% reduction of the bulk porosity. This structure locally becomes more dense but the global effect of compaction is minor, suggesting that low-velocity accretion does not lead to a ‘bunch of grapes’ structure with large internal cavities but a more homogeneous interior, consistent with Rosetta findings. The mild local compaction associated with accretion is potentially the origin of the observed nucleus layering. In 2D axially symmetric impacts hit- and-stick collisions of similarly-sized nuclei are possible at velocities up to 30 m/s where deformation becomes severe. The bulk porosity is reduced significantly, even at 30–50 m/s relative velocity. To avoid hit-and-run collisions the impact angle must be less than 35 °–45 °from the surface normal at 10 m/s, and even smaller at higher velocities. Impact heating is insignificant. We find that the small cross section of the 67P neck may require a less than 5 m/s impact, unless the cohesion exceeds 10 kPa. We conclude that bi-lobe nucleus formation is possible at velocities typically discussed in hierarchical growth scenarios. Impacts of a 7 m projectile at 10 0–500 m/s create a rimless cylindrical shaft with vertical walls, up to 50 m wide and 70 m deep. These shafts bear some resemblance with the pits on 67P, particularly if the depth-to-width ratio is reduced by nucleus erosion. Collisions between similarly-sized nuclei above 100 m/s lead to complete disintegration, and even small fragments suffer different degrees of compaction. Thus, we strongly doubt that 67P has been subjected to high-velocity collisions by projectiles larger than those that might have formed the pits, or is the fragment of a larger parent body. We suggest that the observed properties of 67P are more consistent with primordial accretion.

Item URL in elib:https://elib.dlr.de/116427/
Document Type:Article
Additional Information:Bisher nur online erschienen.
Title:Low velocity collisions of porous planetesimals in the early solar system
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
de Niem, Detlefdetlef.deniem (at) dlr.deUNSPECIFIED
Hviid, Stubbestubbe.hviid (at) dlr.deUNSPECIFIED
Kührt, Ekkehardekkehard.kuehrt (at) dlr.deUNSPECIFIED
Davidsson, Björnbjorn.davidsson (at) jpl.nasa.govUNSPECIFIED
Date:2018
Journal or Publication Title:Icarus
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:301
DOI :10.1016/j.icarus.2017.09.024
Page Range:pp. 196-218
Publisher:Elsevier
ISSN:0019-1035
Status:Published
Keywords:Collisional physics Comets Origin Impact processes
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):Vorhaben asteroids and comets
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Asteroids and Comets
Deposited By: Niem, Detlef
Deposited On:01 Dec 2017 08:57
Last Modified:06 Sep 2019 15:26

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