Experimental investigations of the optical and physical properties of interstellar and lunar dust grains.

摘要

Dust grains constitute a major component of matter in the universe. About half of all elements in the interstellar medium (ISM) heavier than helium are in the form of dust. Dust particles are formed in astrophysical environments by processes such as stellar outflows and supernovae. Ejected into the ISM, they lead to the formation of diffuse and dense molecular clouds of gas and dust. The gas and dust in the interstellar clouds undergo a variety of complex physical and chemical evolutionary processes leading to the formation of stars and planetary systems, forming a cosmic dust cycle. Micron/submicron size cosmic dust grains have a significant role in physical and dynamical processes in the galaxy, the ISM, and the interplanetary and planetary environments. Therefore, the knowledge of the physical, optical, and charging properties of the cosmic dust provides valuable information about many issues related to the role of dust in astrophysical environments.;An experimental facility based on an electrodynamic balance (EDB) has been developed at NASA- Marshall Space Flight Center (MSFC) for investigation of several different properties and processes of individual, levitated micron/submicron size dust grains in simulated space environments. This dissertation focuses on experimental investigations in the following areas: (1) Radiation pressure on individual micron-sized dust grains; (2) Rotation and alignment of micron-sized dust grains simulating rotation of dust grains in astrophysical environment; (3) Charging of analogs of individual cosmic dust grains and lunar dust grains by UV radiation; (4) Charging of Apollo 11 & 17 lunar dust grains by electron impact simulating the charging of lunar dust by the solar wind plasma.;The experimental results obtained on individual micron/submicron-size dust grains in the EDB facility at NASA/MSFC in each of the above four areas were unique and first to be reported. Experimental studies of the physical and optical properties of individual micron-size dust grains provide valuable information about physical and dynamical processes in astrophysical environments that cannot obtained in the laboratory with bulk materials.