SPACE AND COSMIC RAY PHYSICS SEMINAR

University of Maryland
Atlantic Building, Room 2400
4:30 PM Monday, April 20, 2009
Coffee, Tea & Snacks 4:15-4:30 PM

William M. Farrell
Goddard Space Flight Center
Mars Dust Storms, Electric Fields, and Associated Chemistry

It is well-known that small particles of differing composition and size will exchange charge via contact electrification or “tribo-electrification”. On Earth, mixing grains in dust devils have been found to generate electricity via tribo-electric processes. When in collision with the ground or surface, smaller grains tend to obtain a negative charge polarity while heavy grains/surface contain an equal and opposite positive charge. Due to vertical winds, the small negative grains are lofted high into the storm thereby generating a charge separation into a dipole and thus creating macroscopic electric dipole moment within the storm. Electric fields in terrestrial dust devils have been measured to exceed 100 kV/m in a coherent, dipolar configuration that is consistent with a dipole moment oriented downward (negative charge at higher altitudes). We discuss some of our desert studies of such dust devils and show observational evidence for these large fields. It is believed that similar processes occur in Martian dust devils and storms, giving rise to large dust storm E-fields. Since electrical breakdown of a low pressure CO2 gas is 20-30 kV/m, we have suggested that the storm E-fields may become the source of a mildly-ionized gas forming a possible glow discharge. Such discharges have in fact been observed in the lab. We present a model of the electron avalanche process that is suspected to occur in such electrified dust devils/storms and discuss the associated plasma chemistry that may alter the lifetime of some critical Martian atmospheric species like methane.


Sponsored by: Department of Physics and the Institute for Physical Science and Technology, University of Maryland. For information call Victoria at (301) 405-4811 or go to the UMD Space Physics group seminar web site.

There is free parking after 4:00 PM in lot B (the big parking garage across the street from the ATL building). There are a limited number of spaces in lot Q next to the new ATL wing with free parking after 4PM even when there is a basketball game on campus.