[meteorite-list] Parent Bodies Galore?

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:10:08 2004
Message-ID: <3E9B8F73.1198274D_at_bhil.com>

Hi,

    Quite apart from whether or not we could identify meteorites from these
other bodies (which is another question altogether), first order of business
is to determine the probabilities of rocks getting from there to here.

    Back in the 1980's, Fred Singer (ever the practical man) proposed that
the first Martian mission should be to the Martian moons. As I recall, the
energy requirements were much lower than for a Martian landing mission. In
fact, there has long been arguments about whether a man could run fast enough
in the low gravity of Deimos to achieve escape velocity (he couldn't if he
couldn't run faster than on Earth). Some have suggested that only a pole
vaulter could achieve escape velocity. Arthur C. Clarke suggested a runner
could escape if he build a ramp to take off from. It's a fun bit of
arithmetic. (Without the ramp, he could only orbit Deimos.)

    The point is: escaping the gravity of either Martian moon is ridiculously
easy. This suggests that it would very easy to generate a spalled rock that
would escape Martian gravity altogether. Of course, the collisional cross
section of both moons is only about 1/125,000 of Mars, but if it were 12,500
times easier to knock a rock off Phobos or Deimos than off Mars, the
likelihood would be that we would have 1/10 as many Martian moon meteorites
as we have Martian meteorites, or that 2.5 to 3 MMM's (Martian Moon
Meteorites) have been collected and we don't know it (since we can't identify
them).

    My math-at-midnight skills are not up to this, but I think Francis has
had one of those why-didn't-I=think-of-that ideas. The studies done so far
have only focused on major bodies. Nobody thought to calculate the
likelihoods for the smaller bodies, I'll bet. Silly, because we already know
the contribution of smaller asteroidal bodies is substantial.

    "Exploring" the asteroids and other bodies of the solar system by
analyzing the rocks from them that make it to the Earth is an astounding
achievement. BUT there's no substitute for GOING THERE. If we didn't already
have moon rocks, would we have been able to identity a moon rock on the Earth
when we found one?

    Imagine you are the leading lithologist of the Planet Firdapzigble. A
space-faring friend of yours, the captain of a UFO, drops off a gift: 62,000
rocks collected at random by his drunken crew as souvenirs on a distant
planet called "Urth," or something like that. He asks you to reconstruct the
entire cosmic history and physical characteristics of that faraway planet by
analyzing the rocks. You wave your tentacles in dismay.

    We've had a couple of centuries of unlimited access to our own planet and
we haven't figured out everything yet. Field work, we want field work!


Sterling K. Webb
-----------------------------------------------------------------------------

Ron Baalke wrote:

> >
> > Dear List,
> > With Moon meteorites, Mars meteorites, and Mercury
> > meteorites now possible, it's also important to
> > inquire whether there are Phobos meteorites, Deimos
> > meteorites, Amalthea meteorites, etc. especially
> > since these primitive bodies tend to resemble many
> > other ordinary meteorites anyway.
>
> Anything is possible, but the only specific parent bodies we
> can currently correlate meteorites with any reasonable certainty
> are Mars, the Moon and Vesta. There are no confirmed
> meteorites from Venus or Mercury. There are a couple of suspects,
> but it is based more on speculation than hard evidence. The
> main problem with identifying meteorites from Phobos and Deimos
> is that we currently cannot differentiate any possible meteorites
> from these satellites from similiar-type asteroids (Phobos and Deimos are
> very likely captured asteroids). Likewise, trying to match
> up ordinary chondrites to a specific body will also be
> problematic if there are many candidates, and can only be done
> if there is something very unique about its composition.
>
> Ron Baalke
>
Received on Tue 15 Apr 2003 12:49:56 AM PDT