Impact jetting of water ice, with application to the accretion of icy
planetesimals and Pluto

by: Mckinnon, W. B.

ABSTRACT

Jetting can occur during oblique impacts of water-ice bodies at relative
velocities as low as 500 m sec, because of the low Hugoniot elastic limit
and high compressibility of ice compared to rock. In jetted ice, incipient
melting, complete melting, and incipient vaporization occur, upon release
to low pressure, at impact velocities of 1.3, 2.0, and 2.7 km sec, respec-
tively, much less than the 3.4, 4.4, and 5.3 km sec, required in head-on
collisions. Uncertainties in the shock equation-of-state may allow complete
melting during jetting of relative velocities as low as 1.2 km sec. Because
jet speeds exceed impact speeds during the accretion of icy bodies greater
than a few 100 km in radius, there may be a significant loss of icy material.
Thus, jetting during a Charon-forming collision (and not vaporization) may
account for Pluto-Charon's relatively large rock ice ratio, should the CO
ratio of the solar nebula turn out to be too low to sufficiently raise the
rock ice ratio of outer solar nebula condensates by formation of nonconden-
sable CO.

Geophysical Research Letters, ISSN 0094-8276, vol. 16, Nov. 1989, p. 1237-
1240.