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KeywordsCentral Plateau Habitable Zone Crater Diameter Strength Mismatch Crater Morphology
Ring-mold craters (RMCs) are rimless, concentric crater landforms with a circular outer moat and a variety of interior morphologies including central plateaus, pits, bowls, mounds, or multiple rings (Fig. 2), and they are named for their similarity to the cooking implement called ring mold (Kress and Head 2008). Ring-mold craters are best observed on images with a spatial resolution of 10 m/pixel or better (Pedersen and Head 2010).
Ring-mold craters are small-scale craters with diameters ranging from ca. 50 m to <1 km with observed average diameter between 100 and 200 m. Ring-mold craters are typically larger than the associated bowl-shaped craters, which also are found in lineated valley fill, lobate debris aprons, and concentric crater fill (Baker et al. 2010; Kress and Head 2008; Ostrach et al. 2008).
Ring-mold craters form in ice-rich substrate covered by an ice-poor debris till (Fig. 1).
Deuteronilus Mensa, Mamers Valles, Ismenius Lacus, Protonilus Mensae, Utopia Planitia, Mars.
The observation of ring-mold craters is very important because ring-mold craters can be used to detect debris-covered glacial ice and to estimate the depth to the ice table by calculating the maximum depth of the associated bowl-shaped craters (Kress and Head 2008; Baker et al. 2010; Levy et al. 2010).
If the ring-mold craters are deformed, they potentially indicate viscous flow of the ice-rich deposit after the impact of the ring-mold craters (Orgel 2010), while degraded ring-mold craters can be used for recognition and evaluation of alteration stages of ice-rich material (Pedersen and Head 2010).
Finally, the formation of ring-mold craters influences the use of crater size-frequency distributions because impacts into ice will form larger crater diameter than in, e.g., basalt, thus yielding artificially old ages (Kress and Head 2008, 2009).
Observations of ring-mold craters indicate buried water ice and is a climate indicator providing information on the water reservoir of Mars. Therefore, ring-mold craters can be important for mapping of potential habitable zones on Mars.
History of Investigation
Ring-mold craters were first described as oyster shell craters (Fig. 4) by Mangold (2003) who attributed the interior morphology to degradation of regular bowl-shaped craters through enhanced sublimation of ice. (McConnell et al. 2006; McConnell and Newsom 2007) also related their morphology to the presence of ice suggesting that impact into icy material would be modified by subsequent ice flow and sublimation resulting in inverted crater morphology explaining the central mounds in the interior of the ring-mold craters. Instead of associating ring-mold craters with a sublimation-controlled degradation of bowl-shaped craters, Kress and Head (2008) suggested that the morphology of ring-mold craters rather is a primary feature of impacts into relatively pure ice-rich substrate due to their resemblance with laboratory-generated impacts into ice (Kato et al. 1995).
Origin of Term
Ring-mold craters are named for their similarity to the cooking implement called ring mold (Kress and Head 2008).
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