[My original post from my yahoo address got bounced as spam, so I'll try it from
here.]
Elton,
I am no expert in asteroid families, but possibly I can give a general answer
and cite a paper that may be of interest while we wait for a real expert like
Larry to respond.
A paper that I believe should be available to all online is:
"Impact origin of the Vesta family" by Erik Asphaug, published in Meteoritics &
Planetary Science 32,965-980 (1997)
http://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.1997.tb01584.x/pdf
I'm a bit busy validating NEO candidates at the moment so can't take the time to
read the entire paper, but in a nutshell Ashpaug discusses a mechanism that
created the Vesta family of asteroids about 10 - 100 million years ago.
While HEDs are almost certainly from Vesta the uncertainty about this comes from
the fact that we are sensing the surface from great distance. When DAWN arrives,
I'm sure the answer will become definitive and as I mentioned in a previous
thread, we may even be able to pinpoint where some of our meteorites originated.
Exciting stuff coming in the next few months to be sure!
Most specifically to this question, that of other possible source parents, it is
my belief that this is unlikely. The formation of the Vesta family was a major
impact event. We certainly have not sampled spectroscopically every asteroid,
and I'm sure that we have not yet found every member of the family, mostly due
to size, brightness and circumstance. Small chunks of Vesta in earth crossing
orbits, say 10 meters in diameter, the size that can drop tens of kilos on the
earth's surface, are very difficult to detect. In fact something this size may
only be detected a few days before impact, if at all.
It is my personal opinion that all HEDs can be traced back to Vesta and most if
not all "Vesta-like" V-type asteroids can be traced back to Vesta as well.
More rocks coming through the pipeline, so that's all for now.
Cheers
--
Richard Kowalski
Catalina Sky Survey
Lunar and Planetary Laboratory
University of Arizona
http://www.lpl.arizona.edu/css/
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