Time evolution and temperatures of hypervelocity impact-generated tracks in aerogel

Abstract

Aerogel collectors have been used to capture cometary, interplanetary, and interstellar dust grains by NASAs Stardust mission, highlighting their importance as a scientific instrument. Due to the fragile and heterogeneous nature of cometary dust grains, their fragments are found along the walls of tracks that are formed during the capture process. These fragments appear to experience a wide range of thermal alteration and the causes of this variation are not well understood at a theoretical level as physical models of track formation are not well developed. Here, a general model of track formation that allows for the existence of partially and completely vaporized aerogel material in tracks is developed. It is shown that under certain conditions, this general track model reduces to the kinetic snowplow model that has previously been proposed. It is also shown, based on energetic considerations, that track formation is dominated by an expansion that is snowplow-like in the later stages of track formation. The equation of motion for this snowplow-like stage can be solved analytically, thus placing constraints on the amount of heating experienced by cometary dust fragments embedded in track walls. It is found that the heating of these fragments, for a given impact velocity, is expected to be greater for those embedded in larger tracks. Given the expected future use of aerogels for sample return missions, the results presented here imply that the choice of aerogel compositions can have a significant effect on the modification of samples captured and retrieved by these collectors.