Identifying Dark-Haloed and Non-Dark-Haloed Craters from Fused Lunar Data Sets: A New Look at the Mare Humorum Region of the Moon

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Dark-haloed (DHC) and non-dark-haloed (non-DHC) impact craters excavate materials from beneath the surface, and so probe lunar stratigraphy. DHC’s excavate dark (basaltic) material from beneath high albedo (feldspathic) surface units, while non-DHC’s excavate only high albedo material. Surveys of such craters have been used to identify hidden maria and to infer their lateral extent, thickness, and volume.

Previous work on identifying these craters depended on high-sun-angle imagery to see dark halos. However, the lack of topographic information in high-sun-angle views makes distinguishing between crater ejecta and mare ponds difficult, rendering this technique unreliable. The recent abundance of electronic data allows us to solve this problem by fusing compositional and topographic data.

We acquired Clementine UVVIS and electronic Lunar Orbiter data for the region corresponding to our previous Mare Humorum study. UVVIS data was used to create FeO maps (using Lucey et al. [2000] equations) and colour ratio composites. Lunar Orbiter data was registered and fused to the Clementine data. We also added the DHC map from our previous study. This fused data set allowed us to easily identify both DHC’s and non-DHC’s (plus craters only beginning to excavate basaltic/feldspathic material) and compare the results with previous findings.

DHC’s and non-DHC’s identified in this data set correspond poorly with previous results. Many original DHC’s were found to be incorrectly identified. Numerous new DHC’s and non-DHC’s were discovered. One non-DHC was found to excavate basalts. These findings impact previous estimates of cryptomaria in the region. Further study and recalculation is required.