[meteorite-list] mysterite question

Mon May 2 16:54:32 EDT 2005

Hi,

    Generally, cometary material is considered so weak that it couldn't survive even a gentle impact, but we could be wrong about that.  However, another thing to bear in mind is that the meteorites we have do not sample all the bodies in the asteroidal zone.  Something else besides a comet
could be responsible for a strange inclusion material.
    In fact, our sample received here on Earth is very biased toward the inner zone, which is only reasonable considering that the Earth is an interior body to the zone.  There are more than 80 spectral classes of asteroidal bodies, and most of them do not correspond to the properties of any
meteoritic material we know of.
    In the outer portions of the asteroidal zone are many types of bodies with compositions that are probably unlike anything we are familiar with.  We make some (many) assumptions about what we think they may be like, but who knows?  What would a meteorite from a class D or P asteroid be
like, super-carbonaceous or not?
    As for collisions, the asteroidal zone cannot have formed  by objects bonking into each other until they were churned into rubble.  There are too many big asteroids and too few little ones.  Ceres alone contains more than half the total mass of all the asteroids in the solar system!  If
asteroids had gone through this collisional process there would be a jillion trillion tiny sand-grain particles and the asteroid zone would be a bright reflective band along the ecliptic!  (Like the Zodiacal Light only more so.)  It isn't, so there aren't any small pieces.
    No, the asteroidal zone seems to have started out as a collection of pretty good-sized objects, a couple of hundred kilometers up to a thousand kilometers across.  Yeah, there have been some traffic accidents along the way.  It's kind of a mystery why there isn't more mass in the zone, but
big bad Jupiter probably snatched up everything it could early on...  We think, but there could be other explanations.
    There is no reason why solar left-overs like the asteroids should not all have more-or-less circular orbits in the plane of the system if they formed in place like everything else in the solar system, but they do not.  Many asteroids (whole families of asteroids) have high inclinations or
eccentricities.  They have suffered perturbation encounters that have altered their orbits by the magnitude of delta-v of about 5 km/sec or more.  Jupiter could never have done that.
    In general, very close encounters with some perturbing object impart a change in velocity for the perturbed body that is about the same as the perturber's escape velocity, in this case about 5 km/sec.  Well, a body with an escape velocity of 5 km/sec is not some rogue asteroid; it is
roughly the size of  Mars!
    That is a pretty substantial object to have gone blundering into and then out of the asteroidal zone.  I say, out of, because where is it now?  Did we miss a planet?  And, we are not talking about events back at the time of solar system formation or in the early wild-and-wooly days; a
large body in the asteroidal zone would have prevented its formation and accreted itself into a planet.
    No, we're talking about events in the past billion years or so and probably less than a half-billion years ago.  The disturbances in orbits have not "quieted down" enough to be really ancient; they're not "relaxed" as the dynamicists say.  Recent analyses of asteroidal "families" show that
some of them did not form up into families, as we thought, billions of years of years ago, but within only the last few hundred million years.  Practically yesterday.
    I'm just trying to emphasize how much we don't know.  There's lots of stuff out there waiting to be investigated, analyzed, understood; let's land on the rock, kick the regolith, squint at the horizon, start drilling...  Now, let's see, how many field geologists will we need  for the
100,000 biggest asteroids?  How many Toyotas?  How many cooks?  Who's got the map?


Sterling K. Webb
--------------------------------------------------
Darren Garrison wrote:


> On Mon, 02 May 2005 05:19:32 -0700, martinh at isu.edu wrote:

>
> >Hi All
> >
> >Thanks for the link. I have read that article, and in fact, that was what led me to my current confusion. Seems like mysterite is an important discovery, but other than this article (and actually two others) I never see it in print. I guess that is not surprising given its wonderful name.
> >
> >Anyway, I hoped someone could shed more light on this mystery. Just a guess, but if said minerial/material/enrichment/condensate/brecciation called mysterite is what the article's authors suspect, then it could be one of the more important discoveries within meteorites in many years!
> >
>
> Well, if the material is cometary, as some researchers are speculating, I wouldn't be too suprised.
> As many asteroid chuncks are out there and as many comet chunks are out there, I'd think that a
> comet would have had to collide with an asteroid at least once in the past few billion years.  Also,
> I wonder about extrasolar material-- surely, in the lifetime of the solar system, we have
> intersected through some bits of debris that formed around other stars.  Couldn't some of it be
> moving at a relative speed low enough for bits to survive impact?
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