Rodriguez, S., Maurin, A.S., Charnoz, S., Helfenstein, P., D´┐Żau, E., Brahic, A., Evans, M., Dones, L.H.C., Porco, C.C. (2007). "Enceladus regional photometric properties from ISS/Cassini images." American Astronomical Society, DPS meeting #39, #41.09.


Abstract
Saturn's moon Enceladus displays an astonishing diversity of terrain for a 500-kilometer diameter body. Large very old regions covered in craters cohabit with young and fractured terrains which have certainly experienced recent resurfacing. Images from the ISS instrument onboard Cassini show the South Pole, where ice volcanism is more active, has even younger and more fractured appearance than the rest of Enceladus. Photometric studies are a powerful tool to derive surface physical properties, with some, such as grain size or porosity, which can be linked to surfacing mechanisms and thus geological activity. Many analyses of Enceladus' surface photometric properties were already conducted thanks to Voyager and ground-based observations, but they were limited in geometry (only phase angles below 50 degrees for Voyager and below 5-6 degrees for ground-based observations) and spatial resolution, in the sense that only disk integrated photometry of Enceladus was performed. With Cassini and ISS, it is now possible to cover a greater range of phase angle with a better sampling and then obtain a neater and more complete phase function. It is also possible to extract phase function from much delimited regions and then conduct regional analysis. After correction for atmospheric icy particles scattering and thanks to proper phase function modelling (using both Hapke and Shkuratov formalisms), we compare the microscale surface properties derived from the phase functions we extracted in equatorial and northern regions, and in the very young South Pole. By comparing with previous granulometry studies done by the VIMS instrument, we will discuss the implications for terrains formation history.