Meter-scale thermal contraction crack polygons on comet 67P/Churyumov-Gerasimenko
Abstract
Since August 2014, high spatial resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko have been acquired by the OSIRIS camera onboard Rosetta, enabling to identify meter-scale features on the surface (Thomas et al., 2015; El-Maary et al., 2015). Here, we report on the detection and characterization of thermal contraction polygons. We have identified more than 6000 polygons on 67P, using OSIRIS images with a spatial resolution down to 1.6 m/pixel. They are observed in consolidated terrains, from flat terrains to steep terrains such as cliffs and pit walls. The size of polygons is in the range 1 - 10 m, with a mean value of 3 m. Polygons detected on 67P show morphologies with an elevated center. Polygons are known to form on Mars and Earth when the thermal stress of the surface icy materials exceeds their tensile strength, therefore forming fractures (Lachenbruch, 1962; Mangold, 2005; Marchant & Head, 2007). The size, shape and spatial distribution of polygons across the surface provide constraints on their formation and evolution processes, the sub-surface water ice content, the thermal history of the surface and the mechanical properties of the surface material (e.g., Mellon et al., 2008; Levy et al., 2011).