LONG-LIVED GLACIATION IN THE NORTHERN MID-LATITUDES OF MARS: NEW CONSTRAINTS ON ICE VOLUMES AND TIMING

Landforms inferred to have formed as a result of glaciation on Mars are common in the martian mid-latitudes, including concentric crater fill, lobate debris aprons, and lineated valley fill. We have completed new mapping of the spatial extent of these landforms in the northern mid-latitudes (30-50˚N). From these data, we have derived new geometric constraints on the volume of glaciogenic fill in this region, as well as a new assessment of the timing and persistence of glaciation.

Glacial landforms were mapped using mosaics of CTX image data supplemented by mosaics of THEMIS-VIS data. Criteria used to identify glacial landforms include the presence of parallel/concentric lineations, characteristic surface textures, and evidence for flow. From this mapping, we have a preliminary estimate that glacial landforms cover ~5.8 x 10⁵ km² in the study area. This glacial areal extent consists of ~3.5 x 10⁵ km² of LDA, ~1.6 x 10⁵ km² of CCF, and ~0.8 x 10⁵ km² of LVF. We are also using the three-dimensional geometry of these deposits to infer their volume. For the crater fill deposits, the combined volume we estimate is ~4.3 x 10⁴ km³. If this volume is mostly water ice, consistent with our expectations from surface penetrating radar observations, this would be equivalent to a 30 cm thick global equivalent layer calculated from the northern hemisphere mid-latitude crater fill alone. When estimates for other feature classes and the southern hemisphere volumes are included, this value will increase.

During mapping, we also cataloged numerous (>100) synglacial craters, which formed after ice was already present on the surface, but experienced subsequent deposition of ice on their interior. The sizable number of these features is a qualitative indicator that the glacial period during the Amazonian was long-lived. Based on their crater statistics, we estimate that glaciation has occurred for at least 600 My in the mid-latitudes. Glaciation need not have occurred continuously across this entire period, and likely varied in intensity spatially and temporally. However, since accumulation of ice and its survival at the surface are presently not favored in these locations, these observations indicated that during the Middle to Late Amazonian, Mars was commonly in a different climate state than it is today.