36th DPS Meeting, 8-12 November 2004
Session 32 Asteroids
Poster II, Thursday, November 11, 2004, 4:15-7:00pm, Exhibition Hall 1A

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[32.04] NEA 2100 Ra-Shalom: K-class and Source of CV3 Chondrite Grosnaja?

M. K. Shepard (Bloomsburg University), B. E. Clark, S. Swetra (Ithaca College), F. Vilas, K. Jarvis, S. M. Lederer (Johnson Space Center)

We obtained rotationally resolved spectra of the near-Earth asteroid 2100 Ra-Shalom in Aug 2003 in the visible (0.5-0.9 micron) at McDonald Observatory and infrared (0.8-2.5 micron) at the Infrared Telescope Facility (IRTF). Ra-Shalom is one of the larger members of the Aten family. Its effective diameter is ~2.5 km (Harris et al. Icarus 135, 441-450, 1998; Shepard et al. Icarus 147, 520-529, 2000) and its rotation period is 19.8 h (Pravec et al. Icarus 136, 124-153, 1998). Ra-Shalom has been classified as C- (Binzel et al., Icarus 170, 259-294, 2004), S- (Harris et al. 1998), and Xc- class (Bus and Binzel, Icarus 158, 146-177, 2002). Our observations show significant spectral variations with rotation phase, however their proximity to the Milky Way makes interpretation difficult. Our hemispheric-averaged spectrum is an excellent match to the CV3 chondrite Grosnaja, suggesting Ra-Shalom to be its source (RELAB sample MR-MJG-119-P1; Gaffey, JGR 81, 905-920, 1976). Given the purported link between K-class asteroids and CV3 and CO3 chondrites (Bell, Meteoritics 23, 256-257, 1988; Doressoundiram, et al. Icarus 131, 15-31, 1998; Burbine et al. Meteoritics Planet. Sci 36, 245-253, 2001), we suggest that Ra-Shalom is K-class, making it the second known Aten of that class after 1999 JD6 (Binzel et al. Icarus 151, 139-149, 2001). This raises difficult dynamical questions. The major reservoir of K-class asteroids is the Eos family in the outer main-belt (~3 AU). Dynamical simulations by Bottke et al. (Icarus 156, 399-433, 2002) suggest that Atens originate from the 3:1 mean motion resonance with Jupiter (2.5 AU), the nu6 secular resonance (2.1-2.3 AU), or the Mars crossing population (2.1-2.8 AU). Specific computations for Ra-Shalom mirror this (Bottke, personal comm.). Either there is an unknown dynamical path or another K-class source to populate the Atens.

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Bulletin of the American Astronomical Society, 36 #4
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