Monday, March 14, 2005

Stick Ice on Dust: Eases Accretion?

ScienceBlog reports on a PNNL study reporting that ice subliming on dust formed fuzzy crusts that reduced the tendency of dust grains to break apart on collision--and therefore be more likely to coalesce later. They note that the high background radiation in the early solar system would neutralize the naturally forming ice electrets, but note that "chipping" during dust collisions would recharge them. I mused earlier on the "weathering" effects of radiation on space rocks; they noted some natural fluffiness of ice forming at supercold temperatures. Two effects compete here: the "weathering" causes some dislocations but the energy deposited makes it easier to rearrange ice molecules into "less fluffy" configurations. I wonder if they can add radiation to their vacuum chamber. . . Update: Martin Iedema pointed out that the proto-planetary dust clouds were likely to have been thick enough to shield against a lot of the solar wind and cosmic rays. Oops, forgot about that. And he said that if solar wind resulting in compaction of the fluffy ice, this would mainly effect the elasticity rather than the electrical properties of the ice. Cosmic rays, of course, tend to be minimum ionizing at these distance scales, and so don't deposit much energy usable for annealing (though they do result in dislocations). Thanks for the update and correction!

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