[meteorite-list] Meteoroids Before Meteorites

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Fri, 13 Mar 2009 02:54:30 -0700 (PDT)
Message-ID: <497088.24861.qm_at_web55201.mail.re4.yahoo.com>

A good question, Erick.

Unless freshly broken, the opposite is more likely true--meteoroids arrive stealthly and darkly gray to black. A weathered meteoroid looses most of its reflectivity.

By using asteroid spectra and experiments on meteorites there is some good evidence that their surfaces collect "dust", probably dark glass micro spheroids, and ultraviolet exposure darkens the mafic silicates: olivine, bronzite, pyroxenes etc as opposed to the felsic silicates:feldspars which are not directly addressed) I see that there was a formation of a bitumen-like coating (aka tar) on some surfaces in the experiment.

Undisturbed meteoroid surfaces weather via exposure to micrometeorite bombardment, solar wind, and extrasolar radiation and probably accumulation of space dust "bunnies"and possibly water and methane as strange as it seems.

While the coldness of space we think preserves things well, millions of years of agitation and abrasion don't leave surfaces pristine. The result is a darkening of the surface(albedo drop) and a reddening of the spectra. Silicates which are high in iron darken more so apparently. These test results also hint that the depth of color change doesn't penetrate too deeply but they were limited and are short exposures nothing like the typical 4+ billion years of steady exposure in orbit. Formation times are relatively quick calculated at 1,000,000 years or less.

I theorize that most meteoroids are layered in dark dust making them difficult to detect. I haven't heard specifications from the asteroid/meteorite combo 2008 TC3 which landed over Egypt(?) last fall. In that there was such a short lead time I don't know if any before and after spectral comparisons made.

So bottom line both iron and stone meteorites darken with exposure to space. Carbonaceous chondrites are likely to have a tar-like coating. Those coatings are akin to a coat of paint in thickness and would be among the first thing striped away.

Elton


--- On Thu, 3/12/09, Eric Wichman <eric at meteoritewatch.com> wrote:

> From: Eric Wichman <eric at meteoritewatch.com>
> Subject: [meteorite-list] Meteoroids Before Meteorites
> Hi all,
>
> While looking at photos of our most recent extraterrestrial
> visitor, the West meteorite, I was wondering what the
> "meteoroid" looked like while floating around in
> space... Look how nice and white this piece is on the
> "inside".
> http://www.rocksfromspace.org/133g_Interior.JPG Fusion crust
> is only formed while entering our planets atmosphere.
> Meaning that this meteorite was obviously whitish in color
> while still a meteoroid. Right?
>
> Space is a vacuum, and a vacuum preserves things right?
> Look at the moon and all the wonderful craters and how
> wonderfully preserved they are. The moon never changes color
> except when viewed through our atmosphere. From space it
> looks the same as it did millions of years ago.
>
> Does this mean that the West meteoroid, while in space and
> "before" it hit our planet, was white? I mean,
> it's not like the minerals that make up the meteoroid
> change colors before hitting our planet. Right?
>
> I guess the reason I ask this is that we all see photos of
> asteroids that are dark gray, gray-black or brown blobs of
> space rock floating around the solar system. I think our
> perception of meteorites are quite different. We tend to
> think of rocks from space as dark rocks floating around
> aimlessly and randomly bumping into one another occasionally
> sending pieces our way to be pulled in by our planets
> gravity.
>
> Are there huge white rocks floating around out there? And
> if so, wouldn't they be slightly easier to spot than a
> dark blob of an asteroid?
>
> I hope these aren't dumb questions.
>
> Eric
Received on Fri 13 Mar 2009 05:54:30 AM PDT