P31A-1873: Internal Structure of 4179 Toutatis

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Authors: Michael Busch1, Yu Takahashi2, Daniel J Scheeres2, Lance Benner3, Christopher Magri4, Jean-Luc Margot5, Michael C Nolan6, Jon D Giorgini3

Author Institutions: 1. NRAO, Socorro, NM, USA; 2. University of Colorado, Boulder, CO, USA; 3. Jet Propulsion Laboratory, Pasadena, CA, USA; 4. University of Maine Farmington, Farmington, ME, USA; 5. UCLA, Los Angeles, CA, USA; 6. NAIC, Arecibo, Puerto Rico

The 4.6-km-long near-Earth asteroid 4179 Toutatis has made close Earth flybys every four years between 1988 and 2012, and has been observed with high-resolution radar imaging during each approach since 1992 (Ostro et al. 1995, Hudson et al. 1995, Ostro et al. 1999, Hudson et al. 2003, Busch et al. 2012). Toutatis has an elongated bilobate shape and a complex non-principal axis spin state, which can be described as rotation around its long axis with a period of 5.41 days and precession of the long axis around the overall angular momentum every 7.35 days. Due to its elongation and relatively slow rotation, Toutatis’ spin has changed due to terrestrial tides during each close flyby and due to solar tides during each perihelion passage. The maximum spin change was ~0.08 °/day during the 2004 Earth flyby when Toutatis passed within 0.01036 AU ( ‰ˆ4 lunar distances). We have constructed a model of Toutatis’ spin state spanning 1992 to 2012 and have estimated its moments of inertia from its response to known tidal potentials. Toutatis’ moments of inertia about its short and intermediate principal axes as compared to that about the long axis are 3 ± 1% and 4 ± 1% larger respectively than the values expected if the asteroid had uniform density. Material is segregated along the asteroid’s long axis. The observed moment-of-inertia ratios are consistent with a roughly 15% density difference between the lobes and also with more complex internal structures. Near-Earth asteroids can be heterogeneous in composition and/or porosity on kilometer scales. We will test our model of Toutatis’ shape, spin, and interior with additional observations before and after the asteroid makes a 0.04633 AU flyby in December 2012. This will be Toutatis’ last close Earth encounter until 2069.

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