A similarly layered appearance is also visible in the deposits that have built up within the craters themselves, and in the craters’ thick rims. Moving back towards image center, the two largest impact craters visible here are surrounded by double-layered mounds of material. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO Lower parts of the surface are shown in blues and purples, while higher altitude regions show up in whites and reds, as indicated on the scale to the top right. It is based on a digital terrain model of the region, from which the topography of the landscape can be derived. This color-coded topographic image of Utopia Planitia was created from data collected by ESA’s Mars Express on July 12, 2021. These are thick layers of ice- and dust-rich material that have smoothed the surface and were likely deposited as snow back when Mars’ rotational axis was much more tilted than it is today (as was last the case some 10 million years ago). Visible to the left and right of this scene are large, smooth patches of surface known as ‘mantled deposits’. Utopia Planitia is an intriguing and ice-rich region ice has been spotted lying both at and just below the surface, and at greater depths (detected via observations of fresh craters and pits, and by probing Mars’ deeper layers using radar). This plain is thought to have formed as the Utopia basin was filled by a mix of sediments, lavas, and volatile substances (those that vaporize easily, such as nitrogen, carbon dioxide, hydrogen, and water), all transported across the Martian surface by water, wind or other processes. The area outlined by the bold white box indicates the area imaged by the Mars Express High Resolution Stereo Camera on July 12, 2021, during orbit 22150. This suggest that the outer edge of the zone of the polygons and flows may outline the deeper portions of the large body (∼2000 km across) of water/ice that likely existed in the center of Utopia Planitia in late Hesperian.This image from ESA’s Mars Express shows Utopia Planitia, a plain that fills one of three major basins in the northern hemisphere of Mars – Utopia – and has a diameter of 3,300 km, in wider context. The outer (southern) edge of the zone of polygonal troughs and etched flows approximately corresponds to the transition from pancake-like ejecta to rampart ejecta. (7) Etched flows are spatially associated with giant polygons and there is evidence that these features populated the center portion of Utopia Planitia before it was covered by the Elysium-derived units. Their morphology and pattern of degradation, however, are inconsistent with lava and, instead, indicate formation of the flows due to mud volcanism. (6) Etched flows around the central portion of Utopia Planitia were erupted from beneath of the surface of the VB. This pattern of the crater spatial distribution suggests that materials within the center of Utopia Planitia contained more ice/water. Craters with pancake-like ejecta are concentrated within the central portion of the Utopia basin (less than ∼1000 km from the basin center) and rampart craters occur at the periphery of the basin. (5) The diameter ranges of the craters with either rampart- or pancake-like ejecta are overlapping (from ∼2 to ∼60 km). This suggests that these craters formed in targets that contained higher abundances of volatiles. The distal portions of the pancake-like ejecta are heavily degraded (not due to embayment). (4) The majority of the larger (i.e., >1 km) impact craters show ejecta morphologies (rampart and pancake-like ejecta) that are indicative of the presence of ice/water in the target materials. The absolute model ages of etched flows, which represent the upper stratigraphic limit of the VB, are estimated to be ∼3.5 Ga. (3) The SFD of craters that superpose the surface of the VB indicates an absolute model age of ∼3.6-3.5 Ga. (2) Lack of craters that are partly embayed by materials of the VB in the SW portion of Utopia Planitia implies that the emplacement of the VB was faster than the rate of accumulation of impact craters and is consistent with the geologically short time of emplacement of the VB due to catastrophic release of water from outflow channels (e.g., Carr, M.H. (1) The size-frequency distribution (SFD) of craters that both are buried by materials of the Vastitas Borealis units (VB) and superpose its surface indicate that the absolute model ages of terrain predating the emplacement of the VB is ∼3.7 Ga. Results of our detailed geological mapping and interpretation of the nature and relative and absolute model ages of units and structures in the SW portion of Utopia Planitia (20-45°N, 100-120☎) suggest the following.
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