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Peas in a planetary pod? Lunar and mercurian impact basin formation - the same or different?

Ross Potter
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Abstract Text: 

Compared to the Moon, Mercury appears depleted in its number of larger (> 500 km diameter) impact basins, despite it's greater size and, consequently, greater gravitational attraction. Fassett et al. [2012, Journal of Geophysical Research] suggested the paucity of basins could be due to three factors: an observational effect (i.e., data quality), a formational effect (i.e., difference in basin cavity growth) or a later stage post-impact effect (i.e., longterm modification and degradation). In this work, numerical modeling of mercurian basin-forming events was undertaken to directly investigate Fassett et al's [2012] second suggestion. The iSALE shock physics code was used to simulate basin-forming impacts over a wide diameter range (300 to >1500 km), with particular emphasis placed on the Caloris basin, Mercury's largest identified impact event. Results were compared to a vast data set of lunar basin modeling [Potter et al. 2015, Geological Society of America Special Paper 518], focusing on impact mechanic parameters such as excavation depth-to-diameter ratio. Non-dimensional pi-scaling relationships were also used to compare the mercurian basins to their lunar counterparts and craters covering many orders of magnitude in size. The models suggest that the dynamic phase of basin formation on Mercury is very similar to that on the Moon for all impact parameters considered. Some slight differences were present and likely a consequence of Mercury's far higher average impact velocity (42 km/s, compared to 20 km/s on the Moon). This work, therefore, suggests that the paucity of large basins on Mercury is likely to due post-impact processes, such as tectonism and volcanism, rather than an inherent difference in basin formation between Mercury and the Moon.

Joshua Hopkins, Lockheed Martin Space Systems"...
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Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."