Given the estimated population density of LL chondrite NEAs, there are over 8000 candidate bodies less than 100 meters that are high enough in grade to host platinum production. It is important to note that a 100-meter sphere of rock weighs in at almost 1.4 million metric tons, and could contain over 40 tons of platinum at grades measured in meteorite samples. Lewis (1996) estimates that the minimum size that could completely disintegrate during accidental Earth entry is 100 meters, providing an upper size limit for assurance against damage.

From:

The Role of Near-Earth Asteroids in Long-Term Platinum Supply
Brad R. Blair
EB535 Metals Economics
Colorado School of Mines
May 5, 2000
Abstract
High-grade platinum-group metal concentrations have been identified in an abundant class of near-Earth asteroids known as LL Chondrites. The potential existence of a high-value asteroid-derived mineral product is examined from an economic perspective to assess the possible impacts on long-term precious metal supply. It is hypothesized that extraterrestrial sources of platinum group metals will become available in the global marketplace in a 20-year time frame, based on current trends of growth in technology and increasing levels of human activities in near-Earth space. Current and projected trends in platinum supply and demand are cited from the relevant literature to provide an economic context and provide an example for evaluating the economic potential of future asteroid-derived precious and strategic metals.

http://www.nss.org/settlement/...rmPlatinumSupply.pdf

Hey Rusty,
I saw what I thought was a falling/shooting meteor/asteroid around 2am this am in the n nw sky. I don't think it was a shooting star it was too big. Any comments.
Tere

Most meteors are no larger than a grain of sand (which is the size that mostly populates meteor showers, being material shed from comets). But some random meteors are larger,and instead of a short, bright, white streak, will persist longer and sometimes show multiple colors and even a smoke trail. These larger ones are "bolides".

There is no upper size limit in meteors, but one larger than a walnut is rare. Sources can be comets, pieces of asteroids, or chunks of planets ejected into space by meteors hitting them. Pieces of Mars were found in Anarctica.

There is a book by a Russian researcher which contains a great deal of information on asteroids and meteors which may have impacted earth throughout history which can be found and downloaded in PDF format at the following web address:

http://www.scribd.com/doc/2566...ramids-Valery-Uvarov