Redetermination of the space weathering rate using spectra of Iannini asteroid family members

Using the youngest asteroid clusters to constrain the space weathering and gardening rate on S-complex asteroids

“…The characteristic time scale of 570 ± 220 Myr for color change in the main asteroid belt (Willman et al, 2008) is in agreement with pulsed laser experiments (Sasaki et al, 2001) on silicate pellets intended to simulate micrometeorite bombardment. They suggested a characteristic time for weathering of 100 Myr at 1 AU, equivalent to about 700 Myr in the main belt assuming that the Sun is the source of the weathering agent and a r À2 dependence on its strength.…”

“…We have identified three S-complex asteroid clusters amongst the set of clusters with ages in the range 10 5-6 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., Ivezić , Z., Fevig, R. [2008]. Icarus 195,[663][664][665][666][667][668][669][670][671][672][673].…”

“…Their types are consistent with the background population near each object. The average color of the S-complex pairs is PC 1 = 0.49 ± 0.03, over 5r redder than predicted by Willman et al (Willman, M., Jedicke, R., Nesvorný , D., Moskovitz, N., Ivezić , Z., Fevig, R. [2008]. Icarus 195,[663][664][665][666][667][668][669][670][671][672][673].…”

“…Originally proposed (Chapman and Salisbury, 1973) as a solution to the mismatch between the color of the most common meteorites, ordinary chondrites, and their likely source region, inner main belt S-complex asteroids, the space weathering hypothesis is that the surface colors of asteroids change with exposure to the space environment (Hapke, 1973(Hapke, , 1968. The idea has held up to the test of time and in recent years has led to measurements of the rate of color change on S-complex asteroids yielding empirical models that predict the rate of reddening of their surfaces (Jedicke et al, 2004;Nesvorný et al, 2005;Willman et al, 2008). This work extends our space weathering model to the youngest dated asteroids in the main belt that are less than 10 6 years old and, for the first time, measures the surface gardening rate on the asteroids due to impact-generated regolith cycling.…”

“…Willman et al (2008) improved upon the earlier work by refining the color of the [5 Myr old Iannini family, eliminating the Eos family that is no longer considered to be in the S-complex, and carefully refitting the data to the functional form given above to determine PC 1 (0) = 0.31 ± 0.04, DPC 1 = 0.31 ± 0.07, s = 570 ± 220 Myr and a = 0.53 ± 0.19.…”