IGPP Seminar Series

The Role of Plasma Waves in Mars' Atmospheric Loss

by Dr. Bob Ergun
University of Colorado, Boulder


An analysis of recent observations of plasma waves and electron fluxes in Mars' ionosphere indicates that ion heating may have had a considerable impact on Mars' atmospheric loss. We discuss two energy sources of ion heating that can lead to significant ion outflow in the current-day ionosphere and discuss the implications of these process in the past. One energy source is from plasma waves generated by the solar wind interaction with Mars. As these waves propagate into the ionosphere they damp through cyclotron resonance with the O+ population in the upper ionosphere leading to substantial heating and subsequent O+ escape. Another process involves magnetic field-aligned current systems in the cusps of the crustal magnetic fields, again leading to strong O+ heating. These mechanisms can support ~10^25 atoms /s m (~0.4 kg/s) O+ outflow indicated by current observations. We suggest that a stronger source of O+ in the ionosphere ~4 Gyr ago could have lead to losses on the order of 100 kg/s, enough to strip Mars' atmosphere or 10 m of water in a ~0.3 Gyr period. This mechanism may accompany or enhance ionospheric scavenging. The observational evidence for ion heating is, with the current data sets, largely circumstantial so we suggest needed observations.
Tuesday, 07 February 2006
3845 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM