The density of basalt samples from Mare Tranquillitatis and Oceanus Procellarum is 3.36 g/cm3. These basalts should undergo a phase change at a pressure of approximately 10 kbar (200 km lunar depth) that would increase the density to 3.74 g/cm3. This density is substantially higher than the average density of the moon; therefore, lunar maria must be surrounded by a lower density material. The gravity anomaly at Mare Serenitatis, the largest lunar mascon, is so small that only a slender neck of mare material can extend to a source region at depth. No large mass concentrations exist in Mare Tranquillitatis and Oceanus Procellarum; therefore, only a tenuous network of pipes or thin dikes, at most, can connect the vast expanses of basalt on the lunar near side to a source region at depth. A density reversal must be present beneath the maria and Oceanus Procellarum. A good candidate for highland material is a high-aluminum basalt, which has a mineralogical composition similar to that of anorthositic gabbro and a density of 3.0 g/cm3. In the pressure range from 4 to 10 kbar (80 to 200 km in depth on the moon), this highland basalt would undergo a phase transformation with a concomitant density increase to 3.4 g/cm3. With this phase change, a moon composed predominantly of this high-alumina basalt would have the correct density and moment of inertia. For the lunar model proposed in this paper, the maria are areas of 3.36-g/cm3-density material overlying a 3.0-g/cm3-density material that undergoes a gradual phase change to a density of 3.4 g/cm3. In previous work I have hypothesized a modified fission process that would result in the moon having the composition described in this paper.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.