Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1774078 | Icarus | 2010 | 15 Pages |
Abstract
We have extended our earlier work on space weathering of the youngest S-complex asteroid families to include results from asteroid clusters with ages <106 years and to newly identified asteroid pairs with ages <5 Ã 105 years. We have identified three S-complex asteroid clusters amongst the set of clusters with ages in the range 105-6 years-(1270) Datura, (21509) Lucascavin and (16598) 1992 YC2. The average color of the objects in these clusters agrees with the color predicted by the space weathering model of Willman et al. (Willman, M., Jedicke, R., Nesvorný, D., Moskovitz, N., IveziÄ, Z., Fevig, R. [2008]. Icarus 195, 663-673). SDSS five-filter photometry of the members of the very young asteroid pairs with ages <105 years was used to determine their taxonomic classification. Their types are consistent with the background population near each object. The average color of the S-complex pairs is PC1 = 0.49 ± 0.03, over 5Ï redder than predicted by Willman et al. (Willman, M., Jedicke, R., Nesvorný, D., Moskovitz, N., IveziÄ, Z., Fevig, R. [2008]. Icarus 195, 663-673). This may indicate that the most likely pair formation mechanism is a gentle separation due to YORP spin-up leaving much of the aged and reddened surface undisturbed. If this is the case then our color measurement allows us to set an upper limit of â¼64% on the amount of surface disturbed in the separation process. Using pre-existing color data and our new results for the youngest S-complex asteroid clusters we have extended our space weather model to explicitly include the effects of regolith gardening and fit separate weathering and gardening characteristic time scales of Ïw = 960 ± 160 Myr and Ïg = 2000 ± 290 Myr respectively. The first principal component color for fresh S-complex material is PC1 = 0.37 ± 0.01 while the maximum amount of local reddening is ÎPC1 = 0.33 ± 0.06. Our first-ever determination of the gardening time is in stark contrast to our calculated gardening time of Ïg â¼Â 270 Myr based on main belt impact rates and reasonable assumptions about crater and ejecta blanket sizes. A possible resolution for the discrepancy is through a 'honeycomb' mechanism in which the surface regolith structure absorbs small impactors without producing significant ejecta. This mechanism could also account for the paucity of small craters on (433) Eros.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Space and Planetary Science
Authors
Mark Willman, Robert Jedicke, Nicholas Moskovitz, David Nesvorný, David Vokrouhlický, Thais Mothé-Diniz,