A large crater as a probe of the internal structure of the E-type asteroid Steins

Details A large crater as a probe of the internal structure of the E-type asteroid Steins A large crater as a probe of the internal structure of the E-type asteroid Steins

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11c1234j&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P11C-1234

Other

[6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena, [6205] Planetary Sciences: Solar System Objects / Asteroids

Scientific paper

The large crater (2 km in diameter) on the top of Steins, a small diamond-shape asteroid with a diameter of only about 4.6 km, came as a big surprise given the size of the asteroid itself. The asteroid Steins belongs to the rare class of E-type asteroids, which had not been observed by an interplanetary spacecraft before the Rosetta mission of the European Space Agency (ESA) in 2008. The presence of such a large crater poses constraints on the internal structure of the asteroid and on its age estimate based on crater counting. Using our Smooth Particle Hydrodynamics (SPH) hydrocode, we looked for impact conditions and internal structures of the asteroid that allow reproducing this crater. Our code now includes two models of fragmentation, one for solid brittle materials and the other for porous materials. Porosity is in this case defined as the presence of pores whose size is smaller than the thickness of the shock front and the numerical resolution. The presence of such pores can be at the origin of energy dissipation due to compaction during impacts as shown in experiments. It has been suggested in recent years that porous bodies may be able to survive high impact energy events and therefore may host larger craters on their surface than non-porous ones. This idea was supported by the presence of the five large (> 20 km) craters on the 52 km-size asteroid Mathilde. To study the influence of the internal structure on the outcome of an impact, we varied the amount of both micro and macro porosity and also the material strength of the targets. In this way, both monolithic and rubble-pile (macroporous) structures could be considered (either with or without microporosity). The presence of a large crater and our ability to estimate the impact response of a small body using different kinds of internal structure can provide some constraints on the actual internal structure of asteroid Steins. We found that it is possible to reproduce this crater for some but not all of the internal structures considered. However, there are large differences in the formation mechanism of the crater and in the remaining body’s properties and its surface state, depending on the assumed internal structure and strength of the material. This has a great implication on the estimate of Steins’s age based on crater counting. Results of this preliminary investigation that still needs further simulations and analyses will be presented.

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