Science Seminars

9/23/2010 – Formation of the Ganymede/Callisto Dichotomy and Titan’s Interior State from Impacts During the Late Heavy Bombardment

Speaker: Amy Barr
Date: Thursday, Sep 23, 2010
Time: 4:00pm
Location: Duane D-142

Seminar Abstract:

Despite their similar sizes and compositions, Ganymede and Callisto have followed different evolutionary pathways. Ganymede has experienced extensive geological activity and has a large rock core. Callisto’s surface is ancient. Core formation in Callisto has apparently been incomplete; its interior has layers of mixed ice and rock. The Ganymede/Callisto dichotomy could have arisen during an outer solar system late heavy bombardment (LHB) triggered by dynamical events in the outer solar system. Resulting cometary LHB impacts onto Ganymede and Callisto melt their ice/rock surfaces, allowing denser rock to sink to the satellites’ centers. Once core formation in Ganymede or Callisto is 50% complete, it becomes an energetically self-sustaining process (“runaway differentiation”). A 3 dimensional model of impact-induced core formation is used to show that during an outer solar system LHB, Ganymede undergoes runaway differentiation, but Callisto does not, consistent with their present interior states. The interior state of Titan post-LHB and its similarity to estimates of its interior state based on recent Cassini data will also be discussed.