Rehnberg, M., Hedman, M., Burns, J., Tiscareno, M., Murray, C., Evans, M. (2010). "The shapes of the Saturnian Satellites Pallene, Methone, and Anthe" American Astronomical Society, DPS meeting #42, #09.02.


Abstract
We have analyzed photometrically the several hundred available unresolved images of the small Saturnian moons Pallene (S/2004 S2), Methone (S/2004 S1), and Anthe (S/2007 S4) in an effort to constrain their shapes and orientations. Variations in the moons' brightness with viewing geometry are consistent with those expected for synchronously rotating bodies with their long axes pointed at Saturn and their short axes normal to the orbital plane. The moons were modeled as tri-axial ellipsoids with principal axes a (long), b (intermediate), and c (short). The equatorial axis ratio (a/b) is moderately well constrained with values for all three moons likely exceeding 1.3, indicating that all three moons are roughly prolate. Our result for Pallene is within one standard deviation of a previously published value calculated from two resolved images (Porco et al. 2007, Science). The polar axis (c) is poorly constrained for all three moons, due to the lack of high-latitude images. However, we have set lower limits on the c/b ratio for the three moons. We have also constrained the linear phase coefficients for these moons and have sought possible forced librations and/or axial offsets due to internal density inhomogeneities.