Mars's Red (575-625 nm) Seasonal Approximate Reflectivity Averaged Over Mars Years 24-28 From Mars Orbiter Camera

The Mars Global Surveyor spacecraft successfully orbited Mars for over nine Earth years, its instruments returning a plethora of data that still today form important, key data sets in Mars research. A relatively underutilized data set was returned from the Mars Orbiter Camera (MOC), specifically the wide-angle component (MOC-WA), despite returning over 150,000 images in "blue" and "red" wavelengths. The median imaging time of day was 14:00, resulting in few shadows, making it difficult to use for geology, while better cameras arrived within a few years. However, the limb-to-limb coverage of the MOC-WA survey images provides an important resource, where the imaging time that was poor for geology is good for measuring reflectivity. To-date, the only published albedo maps of Mars are from a companion MGS instrument, TES, with wide wavelength coverage and low spatial resolution, and the OMEGA instrument on Mars Express. Modern processing of the MOC-WA images, presented here, allow for the creation of new reflectivity maps in a narrow wavelength range that can be used for photometric control of other data sets and understanding broad-scale surface changes on Mars. Four reflectivity maps were made, at cardinal L-s points, averaging images taken within just a week of each L-s but across multiple Mars years. From these maps, several trends are revealed though most have been previously described, including significant differences in seasonal frost cover surrounding each residual polar ice cap, and significant changes across Syrtis Major, Solis Lacus, and the Tharsis volcanoes. Plain Language Summary The brightness of Mars has been studied for over a century and found to vary on timescales of hours to years, sometimes with patterns and sometimes without. Meanwhile, reference maps of Mars's brightness exist, but only covering all wavelengths of light and averaged over multiple seasons. This work uses the Mars Orbiter Camera from the Mars Global Surveyor spacecraft to produce maps of Mars's brightness in the relatively narrow color range of orange-red. Four maps were made, one for each equinox and solstice. They were made from images taken within just a few weeks of each equinox and solstice, and equinoxes and solstices were averaged together from multiple years. From the images that went into the maps, variation from one year to the next can be isolated geographically, demonstrating such phenomena as dynamic ice caps, polar frost changes, and atmospheric dust and clouds in large impact basins and near volcanoes. Differences from one map to the next show how Mars's brightness changes between seasons, on average, revealing some patterns correlated with geography, and some that are not.