The Youthful Appearance of the 2003 EL61 Collisional Family - Satellite Ejecta Exchange?

Details The Youthful Appearance of the 2003 EL61 Collisional Family - Satellite Ejecta Exchange? The Youthful Appearance of the 2003 EL61 Collisional Family - Satellite Ejecta Exchange?

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.4804r&link_type=abstract

American Astronomical Society, DPS meeting #40, #48.04; Bulletin of the American Astronomical Society, Vol. 40, p.484

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Earlier we showed that three members of the 2003 EL61 collisional family (2002 TX300, 2003 OP32, and 2005 RR43) and 2003 EL61 itself have unusually neutral colors and flat solar phase curves. We now observe a fourth family member, 1995 SM55, with these same traits. These KBOs have photometric properties otherwise seen only for the icy satellites of giant planets[1], known to have surfaces refreshed on timescales of 100 Myr. Also, the EL61 members likely have high geometric albedos (>30%), while other KBOs of comparable size are much darker or redder[2], as expected from cosmic irradiation of organic ice mixtures. Apparently, the family member have young surfaces, at odds with their 1 Gyr dynamical age[3]. While cryovolcanism or atmospheric condensation might periodically recoat 2003 EL61, hiding radiation effects, the other family members are too small ( 200 km) for this to occur[2]. Others have suggested these bodies may be depleted in carbon [2,4]. Instead, we suggest they have normal icy composition but retained small satellites after the parent body's disruption. Multiple binaries are expected in collisions forming asteroid families [5]. Their fresh appearance is then explained by Stern's exchange process [6]. Ejecta from a satellite, generated by meteoroids impacting the satellite, bombard the primary. This requires impacts that excavate unaltered subsurface material, and a sufficient ejecta flux at the primary to cover the surface in 100 Myr. For closely separated ( 1000 km), tidally locked satellites with diameters 50 km, this scenario is plausible.
[1] D. Rabinowitz et al, 2008, AJ, in press; [2] B. Schaefer et al., 2008 DPS meeting (see poster); [3] D. Ragozzine and M. Brown, 2007, AJ 134, 2160; [4] N. Pinilla-Alonso et al., A&A, 468, L25; [5] P. Michel et al., 2001, Science 294, 1696; [6] S. A. Stern, 2008, submitted to Icarus (astroph 0805.3482)

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