Day-to-Day Fluctuations in Mars' Total Electron Content: Implications for Navigation and Position Fixing on Future Missions to Mars.

The Mars Global Surveyor (MGS) radio science experiment has provided the first opportunity to observe martian electron density vs. altitude profiles, Ne(h), on consecutive days. The integral with height of Ne(h) defines the total electron content (TEC) of the ionosphere, a parameter widely used on Earth for geophysical studies. Values of TEC also impose a fundamental limitation on the accuracy of terrestrial navigation and geo-location systems, such as the much-used Global Positioning System (GPS). We have analyzed two sets of MGS ionospheric data (December 1998 and March 1999) to characterize the variability of TEC with the goal of defining possible "space weather" effects on Mars. Computer simulations have been used to characterize the range of magnitudes such TEC-induced fluctuations might pose to GPS-like systems used in future Mars exploration.