Date of Graduation

Spring 5-2015

Level of Access

Open Access

Degree Name

Bachelor of Science

Department or Program

Geology

Number of Pages

98

First Advisor

Gene Clough

Abstract

Impact melt flows form when target material melted by an impact breaches the rim of the impact crater. The melt flows out and away from the crater, forming a lava flow. Such flows have been identified on Venus and the Moon by previous studies. This study aims to document impact melt flows on these two bodies to determine the differences, if any, between them, and to ascertain whether these differences are due to atmospheric conditions. Previously recorded morphological data from Robert Herrick of the Lunar and Planetary Institute and Neish et al. (2014) are used in conjunction with S-band (12.6 cm) radar data from the Magellan spacecraft, the Arecibo Observatory, and the Lunar Reconnaissance Orbiter. It was found that the flow length in terms of crater diameter and CPR, a proxy for surface roughness, are very different for the flows on the two bodies. Venus flows originating from craters with a diameter d ≥ 15 km had an average flow length of 2.33 crater diameters, and lunar flows originating from craters d ≥ 15 km had an average flow length of 0.47 crater diameters. The CPR of Venus flows at radar incidence angles of 40-60° averaged at 0.305 and the CPR of lunar flows averaged at 0.868, meaning that lunar flows are rougher on centimeter scales. These differences are consistent with those that would be produced by the differing surface temperatures on the two bodies; the higher temperature on Venus slows the melt’s cooling rate, decreases its viscosity, slows the increase in its viscosity due to cooling, and increases melt volume. These effects produce longer and smoother flows. Differences in melt composition and impact velocity may also be responsible for these differences. These factors would affect the viscosity and volume of the flows such that Venus flows would be smoother and longer. Further study including thermodynamic and rheological modeling as well as examining impact melt flows on other bodies such as Mars will be necessary to determine what the primary controls on impact melt flow length and roughness are.

Open Access

Available to all.

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