Cratering on Mars with almost no atmosphere or volatiles: Pangboche crater

Abstract

Pangboche crater (17.2°N, 226.7°E; 10.4 km dia.) lies close to the summit of Olympus Mons volcano, Mars, at an elevation of~20.9 km above the datum. Given a scale height of 11.1 km for the atmosphere, this relatively large fresh crater most likely formed at an atmospheric pressure <1 mbar in essentially volatile-free young lava flows. Detailed analysis of Pangboche crater from High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) images reveals that volatile-related features (e.g., fluidized ejecta layers and pitted floor material) are absent. In contrast, abundant impact melt occurs on the floor, inner walls, and rim of the crater, and there is an extensive field of secondary craters that extend up to approximately 45 km from the rim crest. All of these attributes argue that it was the absence of volatiles in the target rocks at the time of crater formation, rather than the thin atmosphere, which had a controlling influence on crater morphology. Digital elevation data derived from the CTX images reveal that Pangboche crater has a depth of about 954 m (depth/diameter = approximately 0.092) and that uplifted target rocks comprise about 58% of the relief of the 180 m-high north rim. As the target material comprised a sequence of layered lava flows, Pangboche crater may well represent the best crater on Mars for direct comparison with craters formed on the Moon (permitting variations in gravitational effects to be investigated) or on Mercury (allowing the role of the atmosphere to be studied).

A depth versus diameter scaling relationship for the best-preserved melt-bearing complex craters on Mars

“…A survey of 50 craters randomly chosen from among the deepest craters in the Robbins and Hynek (2012b) database and 50 from the Boyce and Garbeil (2007) database reveals that only some have pitted materials. Even when considering that not all primary crater-fill deposits are pitted (see Tornabene et al, 2012, andMouginis-Mark, 2015), the results from our survey of these databases reveal significant variations in the fraction of craters with pitted materials and that these constitute only a small fraction of all the "deepest" craters (~14% in Robbins and Hynek (2012b) and 26% in Boyce and Garbeil (2007)).…”

“…Because we have worked with a sample population for which preservation state is nearly uniform, the cause of the variation in depth for any given diameter is likely related either to (a) an inherent property of crater formation that generates the pitted materials, or (b) intrinsic variation in the impact parameters, such as impact angle or velocity, or (c) a target strength property that is not readily recognized from orbital datasets alone (e.g., preferential subsurface zones of weakness). We note that this study cannot account for any additional influences on the initial post-impact formation crater depth that may be a consequence of whether the impact produced pitted vs. non-pitted and lunar-like impactite deposits (e.g., Pangboche Crater: a well-preserved crater with non-pitted and lunar-like crater-fill deposits; see Mouginis-Mark, 2015;Tornabene et al, 2012). However, nonpitted and lunar-like melt deposits are considerably rarer based on a survey by Tornabene et al (2012) (approximately < 5%); as such, we consider the complex crater scaling relationship derived from pitted material-bearing craters in this study to be highly representative of the global population of relatively unmodified craters.…”

Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars

“…Despite previous lack of evidence of impact melts in SNC meteorites, except as shock veins, inevitably they must exist on Mars, given the scale of cratering. Impact melt flows can be recognized at very young craters, like Pangboche on Olympus Mons (Mouginis‐Mark ). Many Mars surface features formed since the late Hesperian, such as dark dunes, dark layers in crater floor deposits, and dark streaks, can be interpreted in terms of impact melt breccias and glassy impact debris (Schultz and Mustard ).…”

Ejecta thickness and structural rim uplift measurements of Martian impact craters: Implications for the rim formation of complex impact craters

“…The differences in the preimpact surface level and a different definition of the boundary of uplifted bedrocks and ejecta deposits on top are the most significant effects to cause the differences in the structural rim uplift values of Mouginis‐Mark and Boyce [] and the measurements in this study (Table ). Mouginis‐Mark [] also derived a structural rim uplift of 140 m and an ejecta thickness of 100 m at the northern rim of the 10.4 km diameter Martian Pangboche crater (17.2°N, 226.7°E). This implies that uplifted target rocks comprise about 58% of the northern rim, which is in good agreement with our findings for complex Martian impact craters.…”