37th DPS Meeting, 4-9 September 2005
Session 36 Icy Satellites I
Oral, Wednesday, September 7, 2005, 11:45am-12:45pm, Law LG19

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[36.05] Saturn's Inner Satellites at True Opposition: Observations During a Central Transit of the Earth Across the Solar Disk

A. Verbiscer (University of Virginia), R. G. French (Wellesley College), P. Helfenstein (Cornell University)

On 13/14 January 2005, the Sun, Earth, and Saturn were so perfectly aligned that, seen from Saturn, the Earth made a central transit of the solar disk, an event so rare that it will not occur again until 2049. A worldwide campaign to view the saturnian satellites in this unique configuration enabled Earth-bound telescopes to obtain observations at the smallest possible phase angle, ~0.02\circ, and consequently measure their true geometric albedos. As part of this cadre of observatories, the Hubble Space Telescope's WFPC2 obtained broadband UBVRI images of Janus, Epimetheus, Mimas, and Enceladus during the Earth transit. When placed on existing WFPC2 phase curves, these data reveal dramatic increases in the brightness of each satellite. Phase coefficients measured from opposition to a phase angle of 1 degree range from \beta ~0.3 mag/deg (at \lambda = 0.43 \mum) for Enceladus to \beta ~0.5 mag/deg (at \lambda = 0.34 \mum) for Epimetheus. The darker, coorbital satellites have stronger opposition surges than do their larger, brighter siblings, Mimas and Enceladus. All phase curves are optimally fit by photometric models whose opposition surges are produced by both shadow hiding and coherent backscatter; the observed opposition surges are too strong to be produced by shadow hiding alone.

This work was supported by the Space Telescope Science Institute and NASA Planetary Astronomy.

If you would like more information about this abstract, please follow the link to http://www.astro.virginia.edu/~av4n/SatOpp05.html. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: verbiscer@virginia.edu

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Bulletin of the American Astronomical Society, 37 #3
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