Comet Nuclei Primordial Aggregation Effects on their Internal Structure

Details Comet Nuclei Primordial Aggregation Effects on their Internal Structure Comet Nuclei Primordial Aggregation Effects on their Internal Structure

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2312l&link_type=abstract

American Astronomical Society, DPS meeting #41, #23.12

Astronomy and Astrophysics

Astrophysics

Scientific paper

Comet nuclei have a low density ( 500 kg.m-3, e.g. [1]) and are easily disrupted. In situ studies have unveiled surface features hinting at a pervasive internal layered structure on 9P/Tempel 1 [2]. This indicates that specific processes occurred during its formation and lifetime.
Our simulations describe the internal structure of comet nuclei due to their formation as aggregates of cometesimals [3]. The simulations take into account the amount of kinetic energy dissipated by sintering processes, the ejection of material during the impact and the variation in density and sizes of the cometesimals. From 10000 to 100000 cometesimals are considered with sizes down to tens of meters. A cohesive strength and density layering of the material occurs, leading to a highly cohesive core with less cohesive outer layers. The thickness of such layers is comparable to the larger layers observed at 9P/Tempel 1 ( 200 m). The porosity also increases with the distance to the centre of the nucleus. The cohesive strength of the nuclei obtained (<104 N.m-2) compares well with values deduced from disruption events observations and laboratory impact experiments.
When the ejected material is lost, the internal structure of the nucleus can be erased. This suggests that either the structures observed are not primordial (cryovolcanism [4]) or that secondary mechanisms, such as the re-accretion of fragments after destructive collision, have occurred during the accretion process [5].
The results are used to improve cometary nuclei models for the analysis of the CONSERT experiment onboard Rosetta, which will study the dielectric properties and internal heterogeneities of the nucleus.
LPI fellowship is acknowledged.
[1] Levasseur-Regourd et al., PSS (2009)
[2] Belton et al., Icarus (2007)
[3] Lasue et al., Icarus (2009)
[4] Belton et al., Icarus (2008)
[5] Blum and Wurm, Annu. Rev. Astro. Astrophys. (2008)

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