Radar Imaging Of 11066 Sigurd, 2000 YF29, And 2004 XL14 And The Obliquity Distribution Of Contact Binary Near-Earth Asteroids

At least 10% of near-Earth asteroids larger than 200 m in diameter observed by radar are contact binaries, which we define as objects composed of two lobes in contact with each other that may once have been in mutual orbit. We will present new shape models and pole directions for three contact binaries imaged by radar: 11066 Sigurd, 2000 YF29, and 2004 XL14. The maximum dimensions for each object are 4.2 km for Sigurd, 0.4 km for 2000 YF29, and 0.3 km for 2004 XL14. Sigurd's lobes are elongated, roughly ellipsoidal, and are joined on their long axis; 2000 YF29's larger lobe is oblate; and 2004 XL14 has lobes that are distinctly angular. Sigurd and 2000 YF29 have obliquities between 50°-130° and 2004 XL14 has an ambiguous obliquity that is close to either 0° or 180°. Of the contact binaries imaged by Arecibo and/or Goldstone, data from eleven are suitable for estimating pole directions. Eight of the eleven objects (73 ± 16%) have high obliquities between 50° and 130°, compared to 40 ± 13% of non-contact-binary single NEAs (10 of 25 objects) and 33 ± 19% of binary NEA systems (3 of 9 objects). Although this is only a marginally-significant detection (95% confidence), estimation of spin vectors from radar observations hints that contact binaries have systematically higher obliquities than other objects in the near-Earth population.