The origin of chondrites: Metal‐silicate separation experiments under microgravity conditions ‐ II

Abstract

[1] In order to understand mechanical processes likely to be occurring on the surfaces of asteroids, we have performed experiments with mineral mixtures on NASA's KC-135 microgravity facility. The behavior of sand and iron filing mixtures, the sand and metal being in the proportions and with grain sizes of ordinary chondrite meteorites, was observed with digital cameras as gas was flowed upward through the mixtures and the plane went through cycles of positive, zero, negative and normal gravity. Partial separation of gas and sand occurred readily under gas flow and microgravity conditions and sometimes survived subsequent turbulence. This behavior is consistent with predictions of the Ergun equation derived from terrestrial experiments. The data have implications for understanding chondrite genesis, for understanding the spectra of asteroid surfaces, and for the design of equipment to function on asteroid surfaces.

Formation of the “ponds” on asteroid (433) Eros by fluidization

“…We concede that in the present experiments our substrates were fairly similar and fairly homogeneous in density. Particle-size sorting occurs rapidly in fluidized beds that are mixtures of differing size and density (Huang et al, 1996;Franzen et al, 2003;Moore et al, 2003).…”

“…In addition, experiments to simulate processes on asteroidal regoliths used a simulant consisting of quartz and iron filings with chondritic Fe/Si ratio. Details of these chondrite simulant experiments were reported by Franzen et al (2003) and Moore et al (2003). In experiments most relevant to the present paper, quartz pebbles (0.5-1 cm in size) were placed on the surface to simulate a coarse-grained fraction (i.e.…”

“…Whereas, Kareev et al (2002) and Haseltine et al (2006) suggested that the trigger to flow could be the release of volatiles from the interior of the asteroid. Franzen et al, (2003) and Moore et al (2003) performed experiments under microgravity conditions and found these fluidization effects were impossible to avoid. Once triggered, they needed very little in the way of a carrier gas.…”

Size and density sorting of metal and silicate grains under microgravity conditions and the origin of chondrites

“…The small diameter of the tubes (tube/grain diameter ratio of ∼10 in some cases) may have resulted in the bed behaving as a plug rather than as a bed of free moving grains. A series of experiments conducted in larger tubes [ Moore et al , 2003] showed that particle separation did occur with the onset of microgravity, but also showed that the entire bed was disturbed and thrown to the top of the tube during periods of negative gravity. In the current experiment, the metal and sand separation would only be preserved if the plunger was lowered prior to negative gravity incursions.…”

“…We have previously reported preliminary data for this flight [ Bogdon et al , 2000] and here we report a more complete summary of the results. Elsewhere we describe the results of our second [ Moore et al , 2003] and third campaigns [ Sears et al , 2002]. Although each campaign had unique objectives and apparatus, collectively they are producing a consistent image of how asteroid regoliths might behave as they are disturbed, either by natural events or by mission operations.…”