Implications of MAVEN’s planetographic coordinate system for comparisons to other recent Mars orbital missions

MAVEN uses a planetographic coordinate system to report altitude, latitude, and longitude on Mars. By contrast, Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter generally used a planetocentric coordinate system. These two coordinate systems are different: latitudes differ by up to 0.34 degrees and altitudes differ by up to 2 km. These differences are large enough to affect the scientific results of comparisons between MAVEN and other orbital datasets. This is illustrated with three examples. (A) Comparisons of neutral density inferred from ionospheric peak altitude could contain errors of 25%. (B) Comparisons of mesopause altitude found from ultraviolet stellar occultations could contain errors of 2 km. (C) Comparisons of zonal variations in thermospheric density found from accelerometer observations could contain errors of 12%. Scientists who compare MAVEN data to other datasets, or to models derived from other datasets, should be aware of these differences in the coordinate systems and make appropriate adjustments. c ©2016 American Geophysical Union. All Rights Reserved.