[meteorite-list] ureilite / venus connection

From: almitt <almitt_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:15 2004
Message-ID: <3B2014B2.3B8D9C6D_at_kconline.com>

Joseph and all,

Here is what Harry Y. McSween has to say about these types of meteorites in his most
excellent book Meteorites and Their Parent Planets.

Ureilite were derived from a body with a particularly complex history. The interior
was partially melted and basaltic magma was extracted. The ureilite residue was then
held at a temperatures of at least 1,250 deg. C for some time, causing it to
recrystallize. The reduction of iron seen in the rims of sensitive silicate grains
suggests reaction with graphite, a reaction that is extremely sensitive to pressure.
Estimates of the pressure needed to account for the compositions of reduced silicates
correspond to depths of approximately 100 km, possibly a minimum size for the ureilite
parent asteroid. Various workers have called on explosive volcanism, shock heating by
impact, or the impact of a carbonaceous asteroid into an already molten body to
explain the curious characteristics of these meteorites. Because of their high carbon
content, ureilites are very dark, with albedos of only approximately 7%. The spectra
of low-albedo members for the S(I) subtype are dominated by olivine and S(II)
asteroids additionally contain a small amount of calcium rich pyroxene. Either of
these sub-classes might correspond to the mineralogy of brachinites.

He goes on to say that the S type asteroids are interpreted to represent potentially a
range of meteorite types from ordinary to primitive achondrites from a small degree of
melting. The diversity in these S type asteroids is probably a direct result of the
igneous processes that many of the these asteroids have experienced.

To me this suggests an asteroid parent body rather than a planetary type body.

--AL

Joseph Hum wrote:

> i would like to hear some feedback concerning the possibleconnection between the
> exotic meteorites- ureilites- and a possible venusian origininstead of just
> dwelling on whether tektites have a lunar origin or notanyway, what about
> UREILITES? Regards, J.K. Hum --- Joseph Hum
Received on Thu 07 Jun 2001 07:56:35 PM PDT