12:00 PM - 1:00 PM
Full Title: A gravity-scaled fracture-formation model and its applications to explain the giant polygons (30-80 km) on Pluto.
Polygon terrains have been observed on the surfaces of many solar system bodies with their horizontal dimensions increasing with surface gravity: polygon dimensions are generally <10s m on Earth (e.g., ice-wedge polygons and mud cracks) but are ~30 km and even up to 80 km on Pluto that has a small surface gravity g = 0.62 m/s2. Assuming that the commonly observed 1:5 scaling on Earth applies to all planetary bodies, the thermal contraction mechanism for the formation of Pluto polygons has been ruled out because the polygon layer thickness on Pluto is believed to be too thin (<500 m) to create the large dimensions of polygons 10s km across. In this talk, I present a new two-layer model that scales fracture spacing with gravity. The model results show that the dimension of polygon size increases exponentially with surface gravity, viscosity of the basal shear zone below the contracting layer, and the shear strain rate. Using the realistic rheological parameters for nitrogen ice, the model explains well the size of the giant polygons observed on Pluto.