AE23A-01 INVITED
Planetary Electrochemical Effects
Lightning on a planet other than the Earth was first discovered by Voyager when it flew past Jupiter in 1979. Since then it has been reported on Saturn by Voyager and Cassini, and on Venus from Pioneer Venus and Venus Express. While lightning involves clouds formed from polar molecules such as water, or vulcanism, dusty environments often create electrostatic fields through triboelectric phenomena. In each instance, changes in local chemistry with profound global impact can occur, such as lightning-induced nitrogen fixation on earth. Perhaps the most dramatic effect occurs on Mars within its global dust storms and dust devils. Enhanced production of oxidants, such as hydrogen peroxide, sulfur and halogen species including perhaps perchlorates from minerals in airborne dust are some of the likely chemical effects. The oxidants may be responsible for the lack of organics on the surface of Mars and rapid destruction of methane in the atmosphere. On Titan, the surface organics may be altered by a different (charged particle) effect, a phenomena that may also operate in the polar regions of Mars and on the Galilean satellites. In this talk, we will discuss possible chemical and astrobiological implications of above electrical processes.
AE23A-02 INVITED
Global Electrical Circuits in Solar System Atmospheres
All atmospheres in the Solar System are slightly electrified by cosmic ray ionization. There is evidence for lightning on Jupiter, Saturn, Uranus, Neptune and Venus, and it could exist, though has not been detected, at Mars and Titan. A comparative approach will be employed to review the role of electrification in the atmospheres of other planets and their moons. The theory, and, where available, measurements, of planetary atmospheric electricity, focusing on ionization and ion-aerosol interactions, will be summarized. The conditions necessary in planetary atmospheres for a global electric circuit similar to Earth's, as developed originally by CTR Wilson, will also be discussed. The gas giant planets appear to be a special case in global circuit terms owing to their unique circumstances of electrical discharges existing in the upper layers of a deep atmosphere. The terrestrial planets may have global circuits analogous to Earth's, but differing in detail. For example, any Martian global circuit is expected to be based on electrical discharges from dust storms.
AE23A-03 INVITED
Dust Charging in Saturn's Rings: Observations and Theory
Saturn's rings show a variety of dusty plasma processes. The electrostatic charging and subsequent orbital dynamics of small grains can establish their size and spatial distributions, for example. Simultaneously, dust can alter the composition, density and temperature of the plasma surrounding it. The dynamics of charged dust particles can be surprisingly complex and fundamentally different from the well understood limits of gravitationally dominated motions of neutral particles or the adiabatic motion of electrons and ions in electromagnetic fields that dominate gravity. This talk will focus on recent Cassini observations at Saturn that are best explained by theories describing the effects of the magnetospheric fields and plasmas on the rings. As our best examples, we will discuss the physics describing the large-scale structure of the E-ring, and the formation of 'spokes' over the dense rings of Saturn.
AE23A-04
The Electrical Environment of the Moon
The discovery of lightning on several gas giants and Venus has captured the imagination of both the public and the scientific community, representing the most dramatic and visible evidence of the ubiquitous nature of atmospheric electrical phenomena in extraterrestrial environments. Small solid bodies with little or no atmosphere are also likely to exhibit active, dynamic electrical phenomena. Here we discuss the Earth's Moon as an example system where electrical effects arise due to the direct action of solar and plasma inputs at the surface. We show data from the Lunar Prospector mission that directly reveal variations in the surface potential of the Moon as a function of solar and plasma conditions, as the solar wind, UV, lunar wake, and the magnetosphere all contribute to the overall current balance at the lunar surface. As with planetary lightning, the extreme events are of special interest, and the Moon is no exception. Rather than resulting from atmospheric disturbances, the Moon's electrical "storms" arise from solar events such as coronal mass ejections, and during interactions with the Earth's geotail. We discuss the implications of lunar surface charging for dust electrification and transport, the dynamics of neutrals and ions, and the potential impact of these processes on the exploration of the surface. As we learn more about the electrical environment at the Moon, we may gain important insights into the detailed physical processes that influence surface charging on other airless bodies as well, such as Mercury, asteroids, and the moons of the outer planets.