Patterned ground in martian high northern latitudes: Morphology and age constraints

We performed a systematic survey of typical surface patterns and small (5–50 m) impact craters in a zone between 50° and 70° latitude in the Northern Lowlands of Mars. We found that small-scale (<10 m) polygonal pattern formed by narrow fractures is typical in the northern half of the studied zone. We interpret this pattern to be formed by active thermal contraction polygons associated with the present-day shallow ground ice. These fresh small polygons are superposed over a larger-scale (∼15–30 m) polygonal network of smooth gentle troughs and mounds. The latter pattern extends southward from the shallow ground ice boundary to the southern edge of the study zone. We interpret this pattern to be a relic from different climate conditions in the geologically recent past (possibly, to the most recent periods of high obliquity of Mars spin axis). The population of small craters is sparse and indicates intensive resurfacing in the recent geological past. The retention age of 5–10 m diameter craters in the northern part of our study zone is surprisingly young, on the order of hundreds to thousands of years, which means that quick obliteration of such craters occurs under the present-day spin/orbit configuration of Mars. The crater obliteration time scale increases for larger craters and toward the southern edge of the study area.