Post by Antoine Séjourné, Univ. Paris-Sud XI, CNRS, Laboratoire IDES, France
On Earth, periglacial regions underlined by continuous and ice-rich permafrost are found in areas of Northern Canada and Siberia These areas are very sensitive to abrupt climate-changes (Murton, 2001). The ice-rich permafrost has a unique assemblage of landforms, some of which are signatures of climate change (Image 1).
On Earth one example are the thermokarst lakes that have resulted from extensive thawing of permafrost following global warming during the Holocene (Czudek and Demek, 1970). Freeze-thaw cycles of the permafrost produce ice-wedge polygons (Washburn, 1973). Localized melting of ice-wedges at the junction of the polygons induces the formation of small ponds of surface water (Washburn, 1973).
The Utopia Planitia region, located in the northern mid-latitudes of Mars contains relatively young landforms (<10 Myr) that are possibly periglacial (Image 2).
The scalloped depressions (100-1,000 m in diameter) are proposed to be the result of sublimation or melting of ground-ice (Morgenstern et al., 2007; Soare et al., 2008). There is a current debate about the development of the depressions, specifically whether they expand equatorward during high obliquity periods, or poleward during low obliquity periods of Mars (Lefort et al., 2009; Séjourné et al., 2011).
The Martian polygons (100 m in diameter) are thought to be formed by thermal-cracking of a permafrost and filling of the cracks with sand or ice (Lefort et al., 2009; Séjourné et al., 2011). Associated elongated pits (10-100 m in diam.) are observed at the junction of some polygons (Image 2). They are proposed to be due to sublimation or melting of ground-ice (Morgenstern et al., 2007; Soare et al., 2008).
The landforms in Utopia Planitia are similar in morphology and scale to the periglacial landforms on Earth (Séjourné et al., 2011). They are part of a landform assemblage indicating an ice-rich permafrost. This permafrost was degraded during a relatively recent obliquity-change of Mars inducing the formation of depressions and pits. The Utopia Planitia landforms described here are probably a marker of a recent climate change that occurred on Mars.
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