SEEKING SAND SOURCES ON MARS

Aeolian processes are one of the dominant causes of modification of the Martian surface today. Sand is pervasive on Mars, even while the contemporary transport of sand at high-threshold wind speeds implies sand breakdown. Thus, detecting the origin(s) of sand on Mars is an important question in Mars science. One long-standing hypothesis for an origin of Martian sand is as volcaniclastic sediments, either epiclastic (from the breakdown of effusive volcanic rock) or pyroclastic (from explosive sedimentation). Recent analyses identified a pyroclastic unit, the Medusae Fossae Formation (MFF) -- more recently mapped as the Hesperian and Amazonian-Hesperian transitional units (Tanaka et al., 2014) -- as an origin of Martian sand. On the basis of this single datum in support of the hypothesis, we continued to test for a volcaniclastic origin of Martian sand elsewhere on Mars. As the previous work had focused on only the western-most (and oldest) portion of the MFF, we inspected the central and eastern portions of the MFF for potential sand-source outcrops with the same suite of characteristics exhibited by the sand-source outcrops identified in the western MFF. We also inspected the five mapped geologic units interpreted as possibly/partially volcaniclastic (including pyroclastic) by Tanaka et al., 2014, namely, the Noachian volcanic edifice unit (Nve), the late Noachian volcanic unit (lNv), the Hesperian volcanic unit (Hve), the Amazonian volcanic edifice unit (Ave) and the Amazonian volcanic unit (Av). In contrast to the results from the western MFF, where the low albedo of the sand indicates ongoing aeolian influences, we found no strong evidence of sand source outcrops within the central and eastern MFF units, nor within the other five units interpreted by Tanaka et al., 2014 as volcaniclastic. This preliminary result suggests that the western MFF units may be more sand-rich than the later MFF deposits and compared to other volcaniclastic units on Mars, or that more detailed analysis and/or data coverage of the other volcaniclastic units is necessary to identify sand-source outcrops. In any case and despite the positive results in the western MFF, the origin(s) of the pervasive sand on Mars remain(s) to be better understood.