Copyright © 2010 by David Roffman. Published by The Mars Society with permission
ENIGMA OF THE MARTIAN ATMOSPHERE:
HIGHER THAN ADVERTISED AIR PRESSURE?
David A. Roffman
Embry-Riddle Aeronautical University
The enigma of dust devils/storms on Mars with a near-vacuum pressure rated at 6.1 mbar at areoid is cause to question accuracy of accepted pressure values. This report includes a review of NASA-archived historical documents, analysis of technical papers, and personal interviews of pressure transducer designers. Only four landers measured pressure ␣ two Vikings, Pathfinder, and Phoenix. Accepted pressures are based on their transducers and radio occultation/spectroscopy by orbiters. Viking transducers were only rated at 18 mbar. Pathfinder and Phoenix could not measure > 12 mbar. Limited sensitivity ranges trace back to Mariner radio occultation results; but Mariners never saw pressures < 2.8 mbar although scale height calculations support pressures on Tharsis summits at ~1 mbar. Martian meteorology is hampered by insufficient wind data by Pathfinder and Phoenix. Pathfinder anemometer calibration efforts failed. There was no anemometer on Phoenix. The Phoenix transducer suffered from an inadequate dust filter, confusion by designers about filter location, and lack of information about nearby heat sources due International Traffic and Arms Regulations. NASA could not replicate dust devils at 10 mbar without employing wind speeds 11 times greater than associated with Martian dust devils, yet dust devils and spiral clouds with ~10 km wide eye walls are seen on Arsia Mons where pressure is ~1 mbar by scale height. Vikings recorded annual pressure fluctuations of 2.1 to 2.6 mbar, attributed to CO2 sublimation at the South Pole, but sublimation of dry ice there cannot result in more than a 0.36 mbar fluctuation. Further pressure questions arise from unexpectedly high densities encountered during aerobraking operations (particularly over the South Pole). Spectroscopy for pressure did not work over ice at the South Pole. Future mission transducers should be capable of measuring a much wider pressure range.