An Impact Genesis for Loki Patera?
What happens when a large impact event takes place on a satellite with a thin crust and lithosphere? In the early Solar System impact cratering and volcanism were the dominate processes shaping the surfaces of the terrestrial planets. Impact events may have triggered additional volcanism by uplifting partially molten mantle material to the surface, where it melts due to pressure release. Subsequently, the shattered crust may have provided pathways for magma to reach the surface creating a longer term hot spot. As the crusts of the terrestrial planets thickened, the ability of impacts to trigger volcanism diminished [1]. However, the highly-volcanic jovian satellite Io is located in a "high-impact" area of the Solar System [2], a victim of material attracted by Jupiter s gravitational field. In 1994 huge impacts were observed when fragments of comet Shoemaker- Levy 9 impacted Jupiter. The large icy satellites of Jupiter (Europa, Ganymede and Callisto) are pockmarked with many impact craters. Yet no impact features have been found on Io [3]. This is because of rapid resurfacing of Io due to volcanism, estimated at approx.1 cm/year [4] which over short geological time erases evidence of impacts. Io, however, has a lithosphere over a molten or partially-molten mantle [e.g., 5], and the effects of a sufficiently large impact may extend far beyond the evolution of the impact crater alone. At least one example of impact-triggered volcanism may exist in the Solar System today: the Loki Patera complex on Io.