spacetoday.net: Impact histories explain differences in Jovian moons

Posted: Tue, Jan 26, 2010, 7:28 AM ET (1228 GMT)
Ganymede and Callisto interior illustration (SwRI)

Differences in the number and velocity of cometary impacts can explain the differences in the surfaces and interiors of two large moons of Jupiter, scientists report. While Ganymede and Callisto are similar in size, Ganymede has clearly differentiated, with any icy surface and rocky interior, while ice and rock are mixed throughout Callisto. Southwest Research Institute scientists find that the differences can be explained by modeling impacts on the moons by comets during the early history of the solar system. Since Ganymede is closer to Jupiter, its gravity focused more comets on that moon, which also impacted at higher speeds. These additional, more energetic impacts created enough heating to melt the moon and allow its ice and rock components to differentiate, something that did not happen on Callisto. The results were published in Sunday's issue of the journal Nature Geoscience.