Conveners:
Michael Mendillo (mendillo@bu.edu), Boston University
Paul Withers (withers@bu.edu), Boston University
2004 Tuesday 29 June 0100-0300 PM
A workshop entitled "Comparative Aeronomy on Earth and Mars" was held on Tuesday 27 July as part of the 2004 CEDAR Meeting in Sante Fe, New Mexico. Approximately 100 people attended. The aim of the workshop was to stimulate an interest in comparative aeronomy among scientists working in terrestrial aeronomy. Speakers were asked to describe some aspect of the aeronomy of Mars in comparison to the Earth's behaviour. Some speakers and audience members also emphasized the benefits of comparisons that include Venus, a terrestrial planet whose aeronomy is understood better than that of Mars, or Jupiter and Saturn, gas giant planets whose atmospheres are dominated by hydrogen and helium and exhibit strikingly different behaviour from Earth.
Michael Mendillo (Boston University) began the workshop with an introduction, explaining how the atmospheres of Earth and Mars are both dominated by molecular, not atomic species, how both ionospheres are dominated by molecular ions that are produced by charge exchange between neutrals and photo-produced ions, how both ionospheres are double-peaked, and how both ionospheres have lower boundaries near 100 km altitude. The ionosphere, exobase, and ionopause regions on Mars span only a few hundred kilometres, one-tenth of their range on Earth.
Jim Murphy (New Mexico State University) discussed thermospheric general circulation models (GCMs) for Earth and Mars. Several different Martian GCMs exist, all deriving from terrestrial GCMs. The many similarities between the atmospheres of Earth and Mars make GCMs more robust on Mars than on any other planet besides Earth. No ground-to-exosphere GCM exists for Mars yet, which makes the upper and lower boundary conditions of any GCM critically important and also impedes accurate modelling of vertically propagating waves and tides. Since there are no measurements of winds in the upper atmosphere of Mars, models play a key role in studies of atmospheric dynamics.
Monica Angelats i Coll (UCLA) discussed tides and gravity waves on Earth and Mars. Mars has much more diurnal heating per unit atmospheric mass than Earth, which generates strong migrating tides, topographic relief of over 20 km, which generates many other tidal modes and waves, and no ozone layer, which encourages vertical propagation of these disturbances. Consequently tides and waves deliver large amounts of momentum and energy to the martian upper atmosphere and perturb it greatly.
Rod Heelis (UT Dallas) discussed the measurements and observations necessary to form a comprehensive picture of the aeronomy of Mars. They are similar to those provided by the Dynamics Explorer mission for the Earth over 20 years ago. Suitable instruments, such as an ion-neutral mass spectrometer, a Fabry-Perot interferometer, a UV spectrometer, a retarding potential analyzer, and a Langmuir probe, have flown on many spacecraft and have a high technology readiness level. Heelis encouraged audience members to attend an August 2004 Mars Aeronomy Workshop, organized by NASA HQ, that will discuss specific opportunities for future spacecraft missions that study martian aeronomy (http://argyre.colorado.edu/life/aeronomy_workshop/).
Paul Withers (Boston University) discussed how to start a research project involving martian aeronomy. All NASA spacecraft data from Mars is freely available at either http://pds.jpl.nasa.gov/ or http://nssdc.gsfc.nasa.gov/planetary/planets/marspage.html. These websites also have useful descriptions of past and future missions, instrumentation, and personnel. General circulation model results are available at either http://data.engin.umich.edu/tgcm_planets_archive/thermo.html or http://www-mars.lmd.jussieu.fr/mars/access.html. The most commonly used reference book is "Mars", published by the University of Arizona Press in 1992 and edited by Kieffer et al. $3M of funding for Mars-related research, including comparative aeronomy, is available from NASA's Mars Data Analysis Program each year.
Geoff Crowley (SWRI) gave a brief presentation on the status of his Mars GCM, which is under development. Several members of the audience discussed comparative aeronomy research further with the workshop conveners during the remainder of the CEDAR meeting. We are hopeful that this workshop has catalysed several new research projects in this area that will be reported at the next CEDAR meeting.