36th DPS Meeting, 8-12 November 2004
Session 24 Icy Satellites
Oral, Wednesday, November 10, 2004, 1:30-3:00pm, Lewis

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[24.03] HST Photometry of Janus and Epimetheus

A. Verbiscer (U. of Virginia)

The spectrophotometric properties of Saturn's small, coorbital satellites Janus and Epimetheus derived from HST/WFPC2 images over the wavelength range 336-1024 nm during the period September 1996 through March 2004 will be presented. Solar phase angles of this large data set range from 0.07 to 6.4 degrees, with nearly complete rotational coverage. The absolute photometric accuracy and high spatial resolution of the WFPC2 enable the determination of geometric albedos in each UVBRI broadband filter and hence colors for each satellite. Previous analyses of HST images by Poulet et al. (1999, J. Geophys. Res. 104, 24095-24110) found Janus to be redder than Epimetheus over the wavelength range 0.3 to 0.7 microns. French et al. (2002, B.A.A.S. 34, 35.11) concluded that the two coorbital satellites have more similar broadband colors, consistent with a common progenitor. We find that the albedo of both satellites increases at longer wavelengths. Epimetheus exhibits a strong wavelength-dependent opposition surge as its albedo increases dramatically at longer wavelengths near opposition, suggesting the presence of the coherent backscatter opposition effect.

This work was supported by NASA through grant number HST-AR-09954.01-A from the STScI which is operated by AURA under NASA contract NAS5-26555.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.