Images of Helene taken by the Cassini spacecraft, with resolutions of up to 24 meters per pixel, show a landscape characterized by broad 2–10 km scale depressions with interior slopes no greater than 12°. These basins are likely the decayed remains of old impact craters. Thin, elongated km-scale raised grooves trace the slopes of many of Helene's basins, likely representing mass flow features and indicating that the moon is undergoing active geologic processes such as
mass wasting and
erosion. Digital elevation models suggest that the grooves have a positive relief of between 50 and 100 meters. Helene has more than 70 craters, while it shows a bimodal appearance—the heavily cratered trailing hemisphere exhibits a crater density ten times greater than the smooth-looking leading hemisphere. Simulation models show that the time series of surface activity on Helene is chaotic.
Surface material Helene's surface material is of relatively high reflectance, suggesting grain sizes between 1 and 100 micrometers. Small craters appear somewhat buried, suggesting recent
accretional processes of some sort. Stress-strain laboratory testing of
impact-gardened lunar regolith samples shows that at low packing densities, they behave like
Non-Newtonian “Bingham” materials, i.e., having the plastic quality of candle-wax and glaciers. This observation suggests that Helene's snow-like surface material may behave as a non-Newtonian mass flow and could be primarily responsible for the visible flow patterns seen on its low-gravity surface. == Gallery ==