Io: Loki Patera as a magma sea

Abstract

We develop a physical model for Loki Patera as a magma sea. We calculate the total volume of magma moving through the Loki Patera volcanic system every resurfacing cycle (∼540 days) and the resulting variation in thermal emission. The rate of magma solidification at times reaches 3 × 106 kg s−1, with a total solidified volume averaging 100 km3 yr−1. A simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations. The Loki Patera surface temperature distribution shows that different areas are at different life cycle stages. On a regional scale, however, there can be coordinated activity, indicated by the wave of thermal change which progresses from Loki Patera's SW quadrant toward the NE at a rate of ∼1 km d−1. Using the observed surface temperature distribution, we test several mechanisms for resurfacing Loki Patera, finding that resurfacing with lava flows is not realistic. Only the crustal foundering process is consistent with observations. These tests also discovered that sinking crust has a “heat deficit” which promotes the solidification of additional magma onto the sinking plate (“bulking up”). In the limiting case, the mass of sinking material can increase to a mass of ∼3 times that of the foundering plate. With all this solid matter sinking, there is a compensating upward motion in the liquid magma. This can be in excess of 2 m yr−1. In this manner, solid‐liquid convection is occurring in the sea.