Asteroid Surface Processes

Our group is currently interested in the formational conditions of meteorites, especially chondritic meteorites. Since nearly all meteorites are believed to be fragments of asteroids that were sent toward earth after a collision, it is necessary to consider what chemical and physical processes could be occurring on asteroids. The recent imaging of asteroids (Sears, 2015) along with theoretical calculations suggest that substantial regoliths (loosely consolidated surface material) up to a few km deep may exist on many asteroids. If asteroids were originally volatile rich (e.g. H₂0) degassing through radiometric and impact heating would have created a "dynamic" regolith.

We suspect that when gases are evolved from a volatile rich CI-like interior pass through the regolith of a 10-100 km parent body, chondrule and metal size-sorting results in surface materials with ordinary chondrite-like properties. Thermal heating of the body could mobilize the entrapped water and create a "fluidized bed". This process could account for particle size-sorting, redox properties of chondrites, oxygen isotopic characteristics, thermal trends, and chondrule formation.

The image to the right depicts a fluidized bed containing simulated asteroid surface material. Quartz sand and iron metal grains were used in L chondrite abundances and sizes. If a gas flow (air) is passed upwards through the column the particles will attain fluid-like characteristics whenever a minimum fluidization velocity is reached. During this stage iron and silicate grains are free to migrate upwards (flotsam) or downwards (jetsam) depending upon their size and density. In this example, the smaller iron grains actually rise to the surface forming an iron rich layer at the top. As a result the bed is increasingly iron-poor with depth. If this scenario ever existed on asteroid surfaces it could explain asteroid spectral properties of metal-rich surfaces as well as meteorites with differing Fe/Si abundance. Sears, D. W. G., 2015. The Explored Asteroids: Science and Exploration in the Space Age. Space Science Reviews, Volume 194, Issue 1-4, pp. 139-235.

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