[meteorite-list] Carbonaceous Comet

[Rob Matson]

Hi Eric/List,

It is still unknown whether main belt asteroid (596) Scheila is a
long-dormant main-belt comet, or if it was simply an impact victim
by a much smaller (and therefore uncatalogued) asteroid. Actually,
these two hypotheses are not mutually exclusive, but I tend to
favor the latter explanation, given that Scheila has been observed
for a century and never exhibited comet-like behavior in the past.
Furthermore, one would expect a cometary outburst to occur closer
to perihelion, which Scheila won't reach for another 17 months.

It would not be the first time (even this year!) that a collision
caused a minor planet to temporarily appear comet-like:

http://www.nasa.gov/mission_pages/hubble/science/asteroid-20100202.html

The spectral studies of Scheila's coma so far indicate dust rather
than volatiles, lending further support to the impact hypothesis.
The morphology of the evolving coma may provide clues as to its
origin, and continued spectral analysis of the coma may reveal
ices, which would tip the scales back in favor of the dormant
comet theory (though quite possible a dormant comet that was
HIT by a much smaller uncatalogued object).

--Rob