LEVITATION AND DYNAMICS OF CHARGED DUST IN THE PHOTOELECTRON SHEATH ABOVE SURFACES IN SPACE

Bodies in space subject to solar ultraviolet flux will emit photoelect rons. At steady state the current of escaping photoelectrons is balanc ed by an influx of particles from the surrounding plasma. When the pho toelectrons dominate the space charge close to the surface, it has pre viously been shown that two steady state potential distributions. can exist, one in which the potential decreases from the surface value to zero monotonically and one in which it decreases to a negative minimum and then increases to zero. It has been suggested that the nonmonoton ic distribution is the stable one. By assuming planar geometry and a M axwellian distribution of the emitted photoelectrons the charging of i solated dust particles in the plasma sheath is calculated for both the monotonic and nonmonotonic potential distribution. By increasing phot oemission from the surface from zero a transition from an ordinary Deb ye sheath above a nonilluminated surface to a photoelectron sheath is simulated. Dynamical properties of the dust particles such as oscillat ions, damping, stability, and trapping are investigated. After being i njected into the sheath or electrostatically levitated, dust may be st ably suspended above illuminated surfaces in space, even in the case o f zero gravitation. However, the smallest particles may escape complet ely from the body. For all sheath types an unstable layer exists close to the surface where dust cannot collect. The theory is applied to bo dies in the solar wind and to the spokes of Saturn.