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| Abstract |
| Binary population among NEAs and beyond | Petr Pravec
Alan W. Harris
| Astronomical Institute AS CR, Ondrejov, Czech Rep.
Space Science Institute, La Canada, CA
| | The photometric data on 18 binary near-Earth asteroids obtained during 1994-2005 (Pravec et al., 2005, Icarus, submitted; Reddy et al., 2005, IAU Circ. 8483) reveal certain characteristic properties of the population of binary NEAs. We review their findings and compare them with data on the first four photometrically detected binaries in the Vesta family and the Hungaria group (henceforth called “VH binaries”; Ryan et al., 2004, Planet. Space Sci. 52, 1093; Bull. Amer. Astron. Society 36, 1181; W.H. Ryan, personal communication; Warner et al., this conference). The data show that the population of small asynchronous binary asteroids extends beyond the region of terrestrial planets and this suggests that the NEA and VH binaries were formed and evolved by similar mechanisms related to their fast spins and rubble pile structure. But there are a few differences. The main difference between the two populations of NEA and VH binaries is that while the former concentrate among asteroids with sizes below 2 km (where we consider secondaries larger than 0.18 Dp where the photometric technique is efficient) and in the range of primary rotation periods 2.2 to 2.8 h, the VH binaries have the characteristics shifted to larger sizes and longer periods; the four known VH binaries are up to 6 km in size and have rotation periods in the range 3 – 4.2 h, i.e., on a tail of the distribution of primary periods of NEA binaries. The specific total angular momentum of most of the binary systems is similar to within +/-20% and close to the total angular momentum of a sphere with the same total mass and density, rotating at the disruption limit. This suggests that the binaries were created by mechanism(s) related to rotation near the critical limit and that they neither gained nor lost significant amounts of angular momentum during or since formation.
The work at Ondøejov has been supported by the Grant Agency of the Czech Republic, Grant 205/05/0604. | | Presenting author: | Petr Pravec |
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