The left side of the image shows a prominent feature of the Utopia basin: depressions up to two kilometers wide and 20 kilometers long intersect to form a polygonal pattern. These depressions are interpreted as grabens that formed a large polygonal structure (see annotated image). The grabens are also visible toward the middle of the image, but they appear to “fade away” and do not show clear borders like those on the left side. This could be because they were infilled by other materials or were not very deep from the beginning. The origin of these grabens is complex and potentially related to the presence of large amounts of water. As part of the northern lowlands, Utopia Planitia was long time hypothesized to have hosted a body of water, possibly a lake or even an ocean, early in Martian history. Utopia Planitia could have accumulated sediments and acted as a sink for sedimentary deposits. Wet, fine-grained sediments would then become compacted and displaced downslope along bedrock slopes of the buried topography. Tectonic processes may also have contributed to the formation of these graben structures. On Earth, seismic surveys have found polygonal graben networks in layers of mudrocks beneath oceans in sedimentary basins. Some graben show a dark layer along their upper edges. These could represent emerging dark, fine-grained ash layers. The depressions continue to the surroundings of the HRSC image and compromise a large area of Utopia Planitia. Read more about the giant graben structure in the press release from 2016: Big, bigger, giant – A former ocean within Utopia Planitia?.