Wb. Mckinnon et Pm. Schenk, ESTIMATES OF COMET FRAGMENT MASSES FROM IMPACT CRATER CHAINS ON CALLISTO AND GANYMEDE, Geophysical research letters, 22(13), 1995, pp. 1829-1832
Chains of impact craters, or catenae, have been identified in Voyager
images of Callisto and Ganymede. Although these resemble in some respe
cts secondary crater chains, the source craters and basins for the cat
enae cannot be identified. The best explanation, proposed by Melosh an
d Schenk, is a phenomenon similar to that displayed by former comet P/
Shoemaker-Levy 9: tidal (or other) breakup close to Jupiter followed b
y gradual orbital separation of the fragments and collision with a Gal
ilean satellite on the outbound leg of the trajectory. Because the tra
jectories must pass close to Jupiter, this constrains the impact geome
try (velocity and impact angle) of the individual fragments. For the d
ominant classes of impactors, short-period Jupiter-family comets and a
steroids, velocities at Callisto and Ganymede are dominated by jovian
gravity and a satellite's orbital motion, and are insensitive to the p
re-fragmentation heliocentric velocity; velocities are insensitive to
satellite gravity for all impactor classes. Complex crater shapes on C
allisto and Ganymede are determined from Voyager images and Schmidt-Ho
lsapple scaling is used to back out individual fragment masses. We fin
d that comet fragment radii are generally less than similar to 500 m (
for ice densities), but can be larger. These estimates can be compared
with those for the Shoemaker-Levy 9 impactors.