ABSTRACT
Titan has an active methane-based hydrologic cycle1 that has shaped a complex geologic landscape2, making its surface one of most geologically diverse in the solar system. Despite the different materials, temperatures, and gravity fields between Earth and Titan, many surface features are similar between the two worlds and can be interpreted as products of the same geologic processes3. However, Titan's thick and hazy atmosphere has hindered the identification of geologic features at visible wavelengths and the study of surface composition4. Here we identify and map the major geologic units on Titan's surface using radar and infrared data from the Cassini orbiter spacecraft. Correlations between datasets enabled us to produce a global map even where data sets were incomplete. The spatial and superposition relations between major geologic units reveals the likely temporal evolution of the landscape and gives insight into the interacting processes driving its evolution. We extract the relative dating of the various geological units by observing their spatial superposition in order to get information on the temporal evolution of the landscape. Dunes and lakes are relatively young, while hummocky/mountainous terrains are the oldest on Titan. Our results also show that Titan's surface is dominated by sedimentary/depositional processes with significant latitudinal variation, with dunes at the equator, plains at mid-latitudes and labyrinth terrains and lakes at the poles.
ABSTRACT
We measure experimentally the penetration depth d of spherical particles into a water-saturated granular medium made of much smaller sand-sized grains. We vary the density, size R, and velocity U of the impacting spheres, and the size δ of the grains in the granular medium. We consider velocities between 7 and 107 m/s, a range not previously addressed, but relevant for impacts produced by volcanic eruptions. We find that dâR(1/3)δ(1/3)U(2/3). The scaling with velocity is similar to that identified in previous, low-velocity collisions, but it also depends on the size of the grains in the granular medium. We develop a model, consistent with the observed scaling, in which the energy dissipation is dominated by the work required to rearrange grains along a network of force chains in the granular medium.