Hamilton, D.P. and J.A. Burns 1993. OH in Saturn's
rings. Nature 365, 498.
Sir - The recent discovery by Shemansky and Johnson of the hydroxyl
radical (OH) in the vicinity of the inner satellites of Saturn is not
surprising since the adjacent moons and rings are predominantly water
ice. However, the amount of OH observed implies a production rate of
the H2O parent molecule that is twenty times greater than theoretical
calculations would suggest. Typical sources for circumplanetary H2O
include collisions of interplanetary micrometeoroids into inner
satellites and rings, and sputtering of these objects by ions and
neutral particles. In order to account for their observations,
Shemansky argues that the interplanetary micrometeoroid flux to the
saturnian system might be twenty times greater than currently
believed. However, such an increased flux would dramatically shorten
lifetimes for the main saturnian rings to darken, for the rings to
spread by angular momentum transfer, and for ring particles to erode
which would make theories of the rings' primordial origin untenable.
Instead we suggest that H20 is primarily produced by collisions of
E~ring grains into the inner satellites of Saturn.
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