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R.J. Bambery, M.D. Hicks, S.H. Pravdo, E.F. Helin, K.J. Lawrence (Jet Propulsion Laboratory/CalTech)
A reliable estimate of the size distribution of cometary nuclei provides important constraints on the formation and dynamical/physical evolution of these bodies as well as their relative proportions in the near-Earth population. The basic data of nuclear sizes has been difficult to obtain, due to the shroud of dust that envelopes the nucleus across a wide range of heliocentric distances. Only two comets, P/Halley and P/Borrelly, have had direct imaging of their nuclei from spacecraft encounters, though high spatial-resolution imaging by the Hubble Space Telescope has also yielded very reliable diameters . Other observers have recently used ground-based photometry to obtain cumulative size-frequency distributions which are not in agreement [2,3]. One possible source of error is the need to include data from a wide range of telescopes and reduction techniques. We shall obtain a new estimate of the size-frequency distribution using a self-consistent data-set.
The Near-Earth Asteroid Tracking (NEAT) Program at the Jet Propulsion laboratory remotely operates two 1.2-meter telescopes at widely geographically separated locations on a near-nightly basis. All NEAT data is archived and publically available through the SKYMORPH website (http:/skyview.gsfc.nasa.gov/skymorph/skymorph.html) Though optimized to discover near-Earth asteroids, we have obtained over 300 CCD images of approximately 40 short and long-period comets over the last 15 months. Though we model coma contamination for all images, we shall concentrate on the fraction of comets at heliocentric distances greater than 3 AU. Our data will be used to derive an independent comet size-frequency distribution .
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.