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Title:
Origin of the Ganymede-Callisto dichotomy by impacts during the late heavy bombardment
Authors:
Barr, Amy C.; Canup, Robin M.
Affiliation:
AA(Department of Space Studies; Center for Lunar Origin and Evolution, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA), AB(Department of Space Studies; Center for Lunar Origin and Evolution, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, Colorado 80302, USA)
Publication:
Nature Geoscience, Volume 3, Issue 3, pp. 164-167 (2010).
Publication Date:
03/2010
Origin:
NATURE
DOI:
10.1038/ngeo746
Bibliographic Code:
2010NatGe...3..164B

Abstract

Jupiter's large moons Ganymede and Callisto are similar in size and composition. However, Ganymede has a tectonically evolved surface and a large rock/metal core, whereas Callisto's surface shows no sign of resurfacing and the separation of ice and rock in its interior seems incomplete. These differences have been difficult to explain. Here we present geophysical models of impact-induced core formation to show that the Ganymede-Callisto dichotomy can be explained through differences in the energy received during a brief period of frequent planetary impacts about 700million years after planet formation, termed the late heavy bombardment. We propose that during the late heavy bombardment, impacts would have been sufficiently energetic on Ganymede to lead to a complete separation of rock and ice, but not on Callisto. In our model, a dichotomy between Ganymede and Callisto that is consistent with observations is created if the planetesimal disk that supplied the cometary impactors during the late heavy bombardment is about 5-30 times the mass of the Earth. Our findings are consistent with estimates of a disk about 20 times the mass of the Earth as used in dynamical models that recreate the present-day architecture of the outer solar system and the lunar late heavy bombardment.
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