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W.J. Merline (SwRI), L.M. Close (U. Arizona), F. Menard (LAOG, Obs. Grenoble, France), C. Dumas (JPL), C.R. Chapman, D.C. Slater (SwRI)
We report on the recent progress of our comprehensive search for satellites of asteroids. In 1998, we began our survey using newly newly developed technologies in adaptive optics to explore the close environs of several hundred main-belt asteroids. Adaptive optics (AO) removes the blurring caused by the Earth's atmosphere and allows diffraction-limited imaging in the near-IR (J-,H-,K'-bands) at the world's largest telescopes. Angular resolutions as high as 0.04 arcsec are possible. We have employed the excellent facilities at the Canada-France-Hawaii Telescope, the W.M. Keck II telescope, and the new Gemini North 8m telescope. Each of these facilities provides unique capabilities and are each complementary to the other.
So far we have discovered or recovered a half-dozen small moons or double asteroids by this AO-assisted direct-imaging technique. Our sample now exceeds 300 main-belt targets, and we have expanded the survey to include near-Earth and Trojan asteroids. Other groups are using AO, direct HST imaging, direct ground-based imaging, advanced lightcurve analysis, and radar techniques to further sample these populations, as well as the Kuiper Belt.
Our results show that the frequency of binary asteroids (at least to our detection limits) is rather small in the main belt, possibly a few percent. Frequencies among other populations, such as the NEAs, are seen to be much higher. We also find that although there are similarities among the detected systems, there are also significant differences. Thus, it is likely that several different formation mechanisms will be required to explain the observed systems. All of the proposed mechanisms for formation involve collisions of one type or another (physical or gravitational).
Study of these systems will provide significant insight to the collisional history and evolution of these asteroid populations. Further, the presence of a companion allows accurate determination of the density of the primary, and thus yields vital information about the composition and structure. Already, we have seen that most asteroids are underdense compared with their likely meteorite counterparts, and thus we must invoke significant empty space or macroporosity in their structure. This work is funded by NASA and NSF.
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The author(s) of this abstract have provided an email address for comments about the abstract: merline@boulder.swri.edu