Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science



Collaborative Specialization

Planetary Science and Exploration


Neish, Catherine N.

2nd Supervisor

Tornabene, Livio L.



In this work, we investigate impact melt emplacement around Martian craters. We compare our results to melt emplacement processes found on Venus, the Moon, and Mercury. We tentatively find Martian melt emplacement more closely resembles Venusian emplacement, rather than lunar emplacement. This suggests Martian melt emplacement likely takes place during the excavation stage where impactor momentum is imparted to the melt. Mercury and Mars have amongst the highest and lowest average impact velocities, respectively, of terrestrial bodies in the Solar System, but a significant difference in emplacement is not observed. This suggests impact velocity may not have as large an influence on melt emplacement as previously thought. It appears lunar melt emplacement is distinct amongst the rocky bodies, where melt is mobilized beyond the crater rim when given additional momentum from central uplift during the modification stage of crater formation.

Summary for Lay Audience

Impact cratering is a geologic process that continually shapes planetary surfaces. Given the high temperatures and pressures experienced during the impact process, some of the planet’s rock will be heated and melted. For this body of work, we investigate how impact melt rock can escape beyond crater rims on Mars. We compare our results to previous results for Venus, the Moon, and Mercury. We investigate how melt is transported and distributed exterior to the interior cavity of the crater. We collect and map high resolution images of the Martian surface in order to determine the distribution of the melt rock. We focus on larger-sized craters, termed “complex craters”, so that we may be consistent with previous studies. Venus and the Moon represent two ends of a spectrum for rocky worlds; Venus is a large world with high gravity, while the Moon is a relatively small world with low gravity. In comparison, both Mars and Mercury have an intermediate gravity. We currently see two distinct trends for how melt rock escapes crater rims; on Venus (and to an extent Mercury), the melt rock seems to escape the crater rim in the middle of the cratering process, while on the Moon, melt rock flows over the crater rim later. We seek to determine at what stage of the cratering process melt rock escapes the crater rim during impact events on Mars. We tentatively find that the Martian processes resemble Venusian processes (and also Mercurian processes to an extent). This suggests three new ideas: 1) Martian melt rock escapes the crater rim in the middle of the cratering process, 2) surface gravity plays the most important role in how melt rock escapes the crater rim, and 3) Venus, Mercury and now Mars have similar melt emplacement processes, while the Moon may represent an unusual case for how melt rock is emplaced beyond the crater rim.

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Geology Commons