[meteorite-list] There are no silly questions? Wait until you haveread that :-)

From: almitt <almitt_at_meteoritecentral.com>
Date: Tue Oct 19 21:09:55 2004
Message-ID: <4175BB4D.26B199AE_at_kconline.com>

Hi Bernhard,

My suggestion is to read Harry (Jr.) McSween's newest book "Meteorites and
Their Parent Planets" as it answers most of the questions you have addressed
with excellent reasons for our believe in what comes from where. A lot of
work has been done with Hubble and it has further verified our suspicions on
certain relations between meteorites and their parent bodies. I might add
that we think with a pretty good degree of certainty that the H class type
meteorites come from Hebe. There are others some more and some less certain.

Here is the not so short answer to two of your questions.

Bernhard Rems wrote:

> 1) HEDs are from Vesta.
>
> Fine. All of them? How comes that with 50.000+ known asteroids, all HEDs
> come from a single one? As far as I know, spectroscopic evidence points
> to Vesta, yes - but how large is the chance that HEDs do NOT come from
> Vesta.

An absence of meteorites consisting of recrystallized ultramafic rock
suggests the parent body hasn't suffered such a catastrophic collision that
it is no longer intact.
The mineralogy of eucrites provides a VERY distinctive reflectance spectrum
with a strong absorption band near 1 um attributable to pyroxene. This was
the first strong evidence we ever had that certain meteorites and Vesta were
probably related.

The brightness of this asteroid (or chips from Vesta, Vestoids) imply a very
limited chance that connection with any other asteroid is very low. No other
V-class asteroids have ever been discovered elsewhere in the solar system
making the correlation between the HED's and Vesta one that can be determine
with confidence.

No doubt the impact at Vesta's south pole (a 460 km impact crater) where some
1% of Vesta's mass was removed is the source of most of our Howardites,
Eucrites and Diogenites. The mapping of the surface by Hubble and the
spectral reflectance and signatures Make the odds of these meteorites coming
from anywhere else nearly 0. (source: "Meteorites and Their Parent Planets").

> 2) Meteorites have been ejected towards earth by collisions between
> asteroids.

As was said early that most likely very few meteorites came to us from direct
impact. Rather between the orbits of Jupiter and Mars are places that are
devoid of asteroids at all. These places are called Kirwood Gaps. These are
areas that have a common ratio of orbit with Jupiter. Examples are a 1:2 or
1:3 or 1:4 and there are many others combinations. When a collision happens
and a meteoroid falls into or near one of these gaps they begin an amazing
process of being perturbed. Each time they make an orbit Jupiter pulls them
out a little farther making a circular orbit an elliptical one. As this
cosmic, rhythmical orbiting continues over the eons it can be pulled out
futher become an Mars crossing, Earth crossing, Venus crossing and even
evidentially end up finding it's way to the sun, in the event it doesn't
collide with the inner planets. Probably this is the biggest source of our
meteorites. I have also read (heard) that the sun can heat the sides of
asteroids up causing them to "gas" also providing a means of them to move out
of a stable orbit and perhaps into one of the Kirkwood gaps.

--AL Mitterling
Received on Tue 19 Oct 2004 09:11:41 PM PDT