Investigation of surface processes on asteroids through laboratory and mission analyses.

摘要

A unique source of information for understanding the nature, origin, and evolution of primitive solar system materials are meteorites and asteroids. However, the connection between meteorites and asteroids is somewhat ambiguous because while the S asteroids are abundant, meteorites matching their spectra are rare, and for the common meteorites types---the ordinary chondrites-asteroids with spectra matching these are atypical. Solving the "S asteroid paradox" or the meteorite asteroid mismatch and corresponding ground-based observational data and laboratory data with the geological context of an asteroid is crucial to understanding the primitive solar system. As a way of providing answers to these questions the Hera Near-Earth Asteroid Sample Return Mission was developed. The science requirements for the mission were outlined by a committee representing the scientific community at a workshop in Los Angeles in 2002. A sample collector was developed at the University of Arkansas that would meet these science requirements as well as the engineering demands. The Touch-and-Go Impregnable Pad (TGIP) has been extensively tested to establish its robustness to a variety of environments it is expected to encounter. Experiments have been conducted to investigate temperature dependency, functionality in a vacuum, radiation hardness, reentry impact survival, outgassing properties, dynamics with an asteroid surface, and a sample cleaning methodology has been developed. The TGIP has performed well in all of the experiments and will be proposed in the 2006 round of the Discovery Program.;Surface processes occurring on asteroids are also significant in understanding a part of the asteroid-meteorite mismatch. Experiments examining fluidization and space weathering were conducted. Two fluidization experiments were flown on NASA's KC-135 microgravity facility examining the separation of fluidized metal and silicate particles in microgravity. Results show that fluidization will cause separation of particles in microgravity conditions but the resulting separation is dependent mostly on particle size and gas flow. The space weathering experiments examined the effect of solar wind on asteroid surfaces with particular interest in the sulfur depletion on the surface of asteroid Eros. Further work on the instrument modified to conduct these experiments needs to be completed to combat a problem with sample contamination.