On the origin of the Pluto-Charon binary

by: Mckinnon, W. B.

ABSTRACT

The normalized angular momentum density of Pluto-Charon (0.45) exceeds the
critical value of 0.39 above which no stably rotating single object exists,
suggesting a collisional origin for this binary. The effects of viscosity
on Pluto's rotational stability and on the density of Charon are considered
. Both a more or less dense Charon would be consistent with a collisional
origin if one (the least massive) or both protoobjects were differentiated.
It is noted that the angular momentum of the system requires the protoob-
jects to be comparably (if not equally) sized if off-center impact velo-
cities vary between escape (about 1.3 km s) and somewhat greater values
(about 2.5 km s) appropriate to Pluto's eccentric and inclined solar orbit.

Astrophysical Journal, Part 2 - Letters, ISSN 0004-637X, vol. 344,
Sept. 1, 1989, p. L41-L44.