Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p51a1175b&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P51A-1175
Physics
5420 Impact Phenomena, Cratering (6022, 8136), 6205 Asteroids
Scientific paper
Studies performed using NEAR spacecraft data have shown that craters on the Eros asteroid can be covered by ejectas from impact events (Thomas et al., 2002) or can be filled by a seismic shaking mechanism (Richardson et al., 2005). In this study, we aim to compute the frequency-size distribution of the craters population on a spherical model representing the asteroid Eros. Although this model is spherical, it has the same average gravity as Eros and the same mean diameter (17 km, Richardson et al., 2005). To create a population of craters, we assume that the craters of Eros have been formed during its stay in the Main Belt. Thus, we adopt the distribution law of projectiles suggested by O'Brien et al. (2006). Once the craters are formed on our model, two kinds of simulations are performed. The first simulation consists in modelling ejecta coverage on the asteroid model. Based on the scaling law method (Housen et al., 1983), the volumes of reimpacting ejectas are computed for each crater and spread on the surface of the modelled asteroid. This leads to ejectas coverage and erasure of several craters. A frequency-size distribution of the craters population can be inferred, accounting for the rate of erased craters. A second simulation aims to quantify the effect of seismic shaking. Based on the normal- mode summation method (Lognonne and Clevede, 2002), maximum accelerations as a function of epicentral distance are computed on the model of Eros for a given seismic source, up to a maximum frequency of 30 Hz. The seismic response of the asteroid behaves linearly with the intensity of the source. Each impactor is then considered as a seismic source having its own seismic momentum, depending on its mass and velocity. From this we can compute the accelerations a given crater is subjected to. Knowing the acceleration history of each crater, we estimate the rate of craters erased by seismic shaking. A second frequency-size distribution of the craters is then computed accounting for craters erased by seismic shaking. Finally, the two frequency-size distributions of the craters (assuming ejectas coverage and a seismic shaking mechanism) are compared to a theoretical frequency size distribution that could occur without crater erasure. These results have direct implications on the estimate we can make of the exposure age of the Eros asteroid. In future work, to make the study more accurate, a three-dimensional model of the shape of Eros will be used and the seismic response of the asteroid will be computed based upon the spectral-element method (Komatitsch et al., 2005). Also, more complex seismic source models will be used in order to assess the saturation of seismic waves for the largest impacts.
Blitz Céline
Komatitsch Dimitri
Le Feuvre Mathieu
Lognonné Philippe
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