LPSC: Lunar Remote Sensing

So this afternoon I attended this session. Pamela had previously suggested I go to the one on Mars impacts, but I was stubborn and thought this one looked interesting too. Reading over her post on it, I will admit to regretting it. My main reaction to this session was Wow… I’m not a geologist. Identifying physical characteristics, age or the chemical abundances of craters just doesn’t do it for me. It’s good to know what I like, I guess (or what I don’t, as the case may be).

Never the less, I was able to take coherent notes on a couple of the sessions. I have one more set of notes that I might be able to turn into a post, but I thought I’d get these up while I remember.
Previously Urecognized Large Lunar Impact Basins Revealed by Topographic Data (Frey H.V.)
MOLA (Mars Orbiter Laser Altimeter) helped us find many impact basins on Mars that were not previously known from image data. The question posed by this group was given this large, previously unknown population of impact basins on Mars, is there a similar such population on the Moon?

To start, they analyzed ULCN topography data in the same fashion as MOLA data has been analyzed. After mapping all circular depressions with diameters greater than or equal to 300km, they found and confirmed the centres and diameters of many already known. They ran into issues because there were 10 that they found centres and/or diameters that were different from those already known.

Previously, we knew of 45 basins with diameters greater tan or equal to 300km. This analysis found 92 basins in this size group. The total population has a crater retention age 1.8 times longer than if you only look at the 45 previously known.

Additionally, it was noted that there are more newly-identified basins on the far side and in the higher latitudes than elsewhere on the lunar surface. They observed the expected exponential increase in number of basins as diameter decreased.

This implies that there is a significant and probably large population of previously unknown, large impact basins on the Moon – which means that we have probably underestimated the total cratering of the Moon.

This is important. Knowledge of lunar cratering rate has a high priority among lunar science objectives. A basic science concept is the bombardment history of the inner solar system is uniquely revealed on the Moon.

Data from LOLA will make it possible to find missing impact basins even smaller in size. This will provide a better estimate of the early Moon cratering rate. From there, we will have a better calibration for the estimated absolute ages of craters on other planets, a better assessment of the Late Heavy Bombardment, and a better understanding of early lunar and planetary evolution.

The Geology of the South Pole of the Moon and Age of Shackleton Crater (Spudis P.D., Plescia J.B., Bussey D.B.J., Josset J.-L, Beauvivre S.)

The South Pole of the Moon is important. It is inside the rim of the largest impact feature, and the unique environment may have resulted in unusual processes and history. We need to understand the geologic setting, as this is a likely site for human and/or robotic exploration.

The SPA basin in this area is expressed by massifs and a large range on topography. The South Pole is within the basin rim, with deeply buried ejecta on inner massifs. Its geological setting is comparable to the apollow 17 site relationship to Serenitatis.

There are three main ways to characterise Massifs. First there are simple scarps, which are step-like linear scarps that mark the rims of the basin. Equaant massifs are block-like mountains that can be found in isolation or in chains. Finally there are platform massifs, which are mesa-like mountains with polygonal outlines and flat tops.

The SPA has both equaant and platform massifs. The presenters wondered if this is caused by post-basin adjustment.

So, the geology of the South Pole is dominated by the SPA basin. Its highlands are heavily cratered and peppered with basin secondaries (mostly from Orientale).

From here they moved on to a discussion of the Shackleton crater. They noticed it appears relatively fresh – does this mean it’s a young crater? They counted superposed craters using SMART-1 and Arecibo. They compared densities with visited and dated sites elsewhere on the Moon.

Their findings imply that Shackleton predates the current lunar spin-axis, and its terrain will not be as steep or blocky as its supposed analogue, Dawes. Shackleton is an Imbrian-age feature with a higher crater density than the Apollo 15 site.

Given that Shackleton occurs on an inner ring massif of the SPA basin, ejecta will consist of basin-related material, both pre-basin bedrock and ejecta/melt breccias associated with basin formation. Other basins (for example, Orientale) have also deposited material near the site.

A lunar outpost near Shackleton would facilitate study of both the materials of the ancient basin and the study of polar volatile deposits. Such an outpost could address significant scientific questions about lunar crustal formation, cratering and volatile history and polar processes.

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