THE MEDUSAE FOSSAE FORMATION ON MARS: HOW BIG WAS IT?

The Medusae Foassae Formation (MFF), Mars, is an enigmatic layered and intensely eroded deposit generally found between approximately 130°E and 230°E and 15°S and 15°N. Multiple hypotheses have been proposed for the precise origin of the MFF, from ancient polar deposits to reworked volcanic ash. Outliers of MFF have been identified tens of kilometers away from the continuous MFF outcrops, suggesting that the presently observed MFF deposits are remnants of a larger, more continuous deposit. Knowing the previous extent of the MFF would provide information about erosional processes operating on Mars since the Hesperian Period, and help to differentiate between possible origins of the MFF.

To constrain the previous extent of the MFF, we developed a weighted matrix of observable morphologies to identify isolated outcrops of MFF. These characteristics are best seen at resolutions better than 250 m/pixel. Characteristics are identified as “excellent,” “very good,” or “good.” An MFF outcrop can be confidently identified by any one of the following options: 1) one “excellent” characteristic; 2) two “very good” characteristics; 3) one “very good” characteristic and two “good” characteristics; 4) or at least four “good” characteristics. An “excellent” observation consists of superposed layered materials, with each layer containing yardangs with distinct orientations. “Very good” characteristics include finding a deposit containing yardangs, showing crenulated margins or visible layers. Observations comprising “good” characteristics include: 1) an unconformable, mantling deposit; 2) consistent surface texture; 3) geographic continuity with known MFF deposits; 4) proximity to known MFF deposits; or 5) aligned depressions (grooves or troughs) suggesting removal of material.

Identification and mapping of formerly unidentified MFF outcrops suggests that the MFF may have once comprised almost twice its current volume, requiring massive redistribution of material on Mars.