Craters, Boulders, and Impact History of Eros

Details Craters, Boulders, and Impact History of Eros Craters, Boulders, and Impact History of Eros

Oct 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.0309c&link_type=abstract

American Astronomical Society, DPS Meeting #32, #03.09; Bulletin of the American Astronomical Society, Vol. 32, p.996

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We report size distributions for Eros craters D>15 m and boulders D>10 m. Although not saturated with giant craters like Mathilde, Eros (like Ida) exhibits empirical saturation for 200m < D <1 km. Craters D<100 m are progressively depleted (differential power-law exponent b -1) relative to the equilibrium distribution for a lunar-like crater production function. Boulders, however, have an extremely steep distribution (b -6). At D<20 m, boulders exceed craters. Eros has 1 million boulders with D>8 m. Eros' fine-scale attributes may not be inconsistent with Ida (minimal resolved boulder D> 45 m [1]). Eros has < 100 Myr lifetime against solar/planetary impact or ejection, so it was cratered mostly while in the asteroid belt. We hypothesize that unexpected attributes of Eros reflect a 100x decrease in cratering rate during the last tens of Myr; orbital simulations [2] suggest Eros had 50% chance of such an impact hiatus since decoupling from the main belt. Such a hiatus might, in several ways, facilitate the preferential degradation/destruction of small craters on Eros, best explained by a non- equilibrium burst (relative to cratering rate) of non-impact-related topographic degradational processes. Instead of an episode of enhanced endogenic activity (the usual explanation for a planet), normally minor, unrecognizable endogenic processes on asteroids (e.g. thermal creep) might be manifest after a long cratering hiatus. Perhaps long-term relaxation from effects of a major impact (e.g. the "saddle" or Psyche crater) persisted into the hypothesized hiatus, including possible reaccretion of transient orbiting debris/boulders but without competition from continuing hypervelocity impacts. Eros' spectral homogeneity (compared with otherwise similar Ida, which has patches of less-weathered ejecta from recent impacts) may also be explained by the hiatus: space weathering may have matured since the last big impact irregularly blanketed Eros' surface. [1] P. Lee et al. (1996) Icarus 120, 87. [2] P. Michel et al. (1998), Astron. J. 116, 2023.

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