J. L. Margot, P. A. Taylor, M. Nolan, E. Howell, S. J. Ostro, L. A. M. Benner, J. D. Giorgini, C. Magri, L. Carter
Observations of (35107) 1991 VH in 2008 provide an exceptional opportunity to characterize the dynamics, morphology, and physical properties of a binary asteroid - two bodies revolving around each other as they orbit the sun. High resolution images will provide detailed information on the size, shape, and spin of the binary components, their mutual orbit, and their dynamical interactions.
In conjunction with pre-existing observations, these data will probe the formation and evolution of binaries in great detail, including dynamical processes such as tidal interactions and librations/tumbling, radiative processes (YORP), and erosional processes such as avalanches and lofting/redeposition of material. The signal-to-noise ratio will exceed 1000 per run, allowing images to be obtained with a spatial resolution as fine as 8 meters. If the observations are successful 1991 VH may become one of the very best characterized binaries in the solar system, comparable to 1999 KW4.
This system has been observed by Pravec et al. (Icarus 133, 1998; Icarus 181, 2006) who detected two, and sometimes three, periods in their lightcurve data, and who identified 1991 VH as a binary system.
2008 July 29 update: First radar echoes show telltale signature of binary system
Here is a plot of our very first radar echoes obtained at Arecibo. The figure shows a wide echo (~11 Hz) due to the primary component, and a narrow peak (< 1 Hz) due to the secondary component. Both components were resolved in images at 300 m and 15 m resolution. We have also obtained precise range measurements which allowed us to improve the knowledge of the trajectory of the asteroid. The data quality will get better every day as the asteroid gets closer to Earth: from 35 lunar distances today to about 20 lunar distances on August 12.
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