Dome Craters on Ganymede and Callisto May Form by Topographic Relaxation of Pit Craters Aided by Remnant Impact Heat
arxiv(2024)
摘要
The icy Galilean satellites display impact crater morphologies that are rare
in the Solar System. They deviate from the archetypal sequence of crater
morphologies as a function of size found on rocky bodies and other icy
satellites: they exhibit central pits in place of peaks, followed by central
dome craters, anomalous dome craters, penepalimpsests, palimpsests, and
multi-ring structures. Understanding the origin of these features will provide
insight into the geophysical factors that operate within the icy Galilean
satellites. Pit craters above a size threshold feature domes. This trend, and
the similarity in morphology between the two classes, suggests a genetic link
between pit and dome craters. We propose that dome craters evolve from pit
craters through topographic relaxation, facilitated by remnant heat from the
impact. Our finite element simulations show that, for the specific crater sizes
where we see domes on Ganymede and Callisto, domes form from pit craters within
10 Myr. Topographic relaxation acts to eliminate the stresses induced by crater
topography and restore a flat surface: ice flows downwards from the rim and
upwards from the crater depression driven by gravity. When the starting
topography is a pit crater, the heat left over from the impact is concentrated
below the pit. Since warm ice flows more rapidly, the upward flow is enhanced
beneath the pit, leading to the emergence of a dome. Given the timescales and
the dependence on heat flux, this model could be used to constrain the thermal
history and evolution of these moons.
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