8009(  1) - 04/16/98 14:17  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      8009
                                                       Version: 1
                                                       Check-in Date: 16-Apr-1998
                                                                      14:13:59

1.Proposal Title:
Asteroid Trails in HST Archive Images
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2. Proposal For  3. Cycle
AR               7
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4. Investigators
                                                                                     Contact?
    PI: Robin Evans                       OAO Corporation
   CoI: Karl Stapelfeldt                  Jet Propulsion Laboratory                     N
   CoI: John Trauger                      Jet Propulsion Laboratory                     N

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5. Abstract

Numerous trails from small, main-belt asteroids can be found in Archival HST images.
Our initial study of the first two years of WFPC2 data (Evans et al. 1998, Icarus in
press) found 230 images with trails from 96 distinct objects. The trails show a
remarkable curvature due to the parallax induced by HST's orbital motion during the
exposures. Using ephemerides for HST, the geocentric distance to each asteroid can
be directly determined from the parallax contribution to the trail shapes. The
availability of accurate distances allowed a meaningful absolute magnitude (size)
histogram to be constructed for these without need of full orbit determinations. We
found evidence for a shallower slope in the asteroid size (magnitude) distribution
function (over the range 20<V<24) than had been extrapolated from larger (brighter)
objects. We propose to extend our initial study by conducting a comprehensive search
for asteroids in WFPC2 and STIS images taken in 1996-97. Based on the Archive
catalogs and previous experience, we expect to find trails from ~ 150 new objects in
these data. The new detections will significantly improve our statistical
determination of the magnitude distribution function for small asteroids, and will
permit investigation of its radial variation within the main belt. The results will
provide a fundamental constraint to models for collisional evolution of the main
belt and a census of a major source region of Earth-crossing objects.
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  Data Distribution

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  Blocking Factor: 10
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                                                8009(  1) - 04/16/98 14:17  - [  2]

            Summary Form for Proposal  8009

  Item                         Used in this proposal
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  Proposal Category            AR
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