Using The Youngest Asteroid Clusters To Constrain The Space Weathering And Gardening Rate On S-complex Asteroids

Details Using The Youngest Asteroid Clusters To Constrain The Space Weathering And Gardening Rate On S-complex Asteroids Using The Youngest Asteroid Clusters To Constrain The Space Weathering And Gardening Rate On S-complex Asteroids

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.3910w&link_type=abstract

American Astronomical Society, DPS meeting #42, #39.10; Bulletin of the American Astronomical Society, Vol. 42, p.1034

Astronomy and Astrophysics

Astronomy

Scientific paper

We 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 ≤5×105 years. We 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)1992YC2. Their average color agrees with the color predicted by the space weathering model. SDSS 5-filter photometry of 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 5σ redder than predicted. 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 so then our color measurement allows us to set an upper limit of 0.64 on the fraction 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 timescales of κw=960±160My and κg=2000±290My 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 Δ PC1=0.33±0.06. Our first-ever determination of the gardening time is in stark contrast to our calculated gardening time of κg 270My 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.

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