Search for Satellites of Vesta: Upper Limits on Size

Details Search for Satellites of Vesta: Upper Limits on Size Search for Satellites of Vesta: Upper Limits on Size

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5306m&link_type=abstract

American Astronomical Society, DPS meeting #41, #53.06

Astronomy and Astrophysics

Astronomy

1

Scientific paper

A search for moons of Vesta was conducted using 40 s exposures with Hubble Space Telescope's Wide Field Planetary Camera 2 on May 14 and 16, 2007. An area roughly equivalent to 1/3 of the Hill sphere was searched. Vesta's Hill sphere radius was 488 Vesta radii at the time (Vesta radius=265 km). Signal from Vesta saturated the detector out to 14 Vesta radii, and the edge of the cameras reached 260 Vesta radii. Sequential exposures were median filtered to remove cosmic rays. Artificial satellites represented by a two-dimensional Gaussian profile of were randomly inserted into the images after determining that orbital motion of a detectable satellite would be negligible. Twenty-seven people searched the images for satellites resulting in a 90% confidence level of 0.2 magnitude precision and a variance of 0.77. Only artificially implanted satellites were found down to a magnitude of 22.5 +/-0.2 by almost all searchers. This is the upper limit to satellite detection. Four dedicated and experienced observers searched all images and found only an asteroid but no moons. The upper limiting magnitude converts to an upper limit of 44 +/-4 m diameter assuming Vesta's albedo and phase function. Knowing that Vesta has a large basin in its southern hemisphere and that the ejecta from that impact likely produced 3-25 km sized bodies, called Vestoids, it is interesting that none of the impact debris remained in orbit around Vesta. Satellite formation by cratering is very inefficient and any satellites that might have formed from such an event would have to survive for billions of years. The Dawn spacecraft will be able to search closer to Vesta upon its approach to orbit in August 2011. Continued searches are warranted for both their scientific interest and support of the Dawn mission.

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