Impactors on Saturn's Regular Satellites: Heliocentric vs. Planetocentric

Details Impactors on Saturn's Regular Satellites: Heliocentric vs. Planetocentric Impactors on Saturn's Regular Satellites: Heliocentric vs. Planetocentric

Apr 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011dda....42.0706d&link_type=abstract

American Astronomical Society, DDA meeting #42, #7.06; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

Voyager-era scientists concluded that Saturn's moons were struck by at least two impactor populations. Population I impactors - most likely "comets" orbiting the Sun - formed most of the larger and older craters, while Population II impactors - possibly Saturn-orbiting ejecta from impacts on satellites - produced most of the smaller and younger craters [1]. Present-day dynamical models predict that "ecliptic comets," which likely originate in the Kuiper Belt/Scattered Disk, are the primary impactors on the regular satellites of the giant planets [2]. However, these models predict vastly more craters on the leading faces of synchronously rotating moons than on the trailing faces [3]; such asymmetries are not observed. The answer to this riddle might be nonsynchronous rotation; crater saturation; or the putative Population II impactors, which should not create strong asymmetries [4]. We focus on Cassini measurements and interpretation of the crater size-frequency distributions on Mimas, Enceladus, and Rhea. Because Mimas and Enceladus have weak gravities, they are excellent sources of Saturn-orbiting ejecta, which usually come back to strike their parent moons, making "sesquinary" craters. Impacts on weightier Rhea are more apt to make traditional secondary craters [5]. We will apply ejecta models [6] to quantify the importance of sesquinary craters on the saturnian moons. The biggest uncertainty is the size of the ejecta [7]. We thank the CDAP program for support. References: [1] Dones L., et al., in Saturn from Cassini-Huygens, pp. 613-635 (2009). [2] Zahnle K., et al., Icarus 163, 263-289 (2003). [3] Zahnle K. et al., Icarus 153, 111-129 (2001). [4] Alvarellos J., et al., Icarus 178, 104-123. [5] Bierhaus E. et al., Lunar Planet. Sci. 42 (2011). [6] Housen K.R., Holsapple, K.A., Icarus 211, 856-875 (2011). [7] Zahnle K. et al., Icarus 194, 660-674 (2008).

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