February 16, 2011
LRO WAC mosaic processed by Maurice Collins
Yesterday Humboldt was seen in an oblique view from Earth and now Maurice has prepared an overhead mosaic from the Lunar Reconnaissance Orbiter Wide Angle Camera images. In it I see things that I didn't know before. In yesterday's LPOD I noted that the low spot on the rim (on the right here) was where Humboldt appeared to overlap a pre-existing crater. I don't think it is a crater but it is strange - there is a somewhat smooth spot and the area is bounded by nearly straight edges, looking almost like artifacts. Another definite crater that was truncated by the formation of Humboldt is at bottom left - it is amazing how this crater could have been right at the edge of formation of a 190 km wide crater and survived. Notice also the dark mare deposits on the floor of Humboldt. Like the slivers of mare in the Orientale Basin, these are all just inside the major faults at the crater walls. These dark deposits also bury the rilles, so the lavas erupted after the rilles formed. The rilles themselves are remarkable - they have both a concentric and radial pattern, but topography does not confirm the assumed doming of the floor. Many of the rilles are composed of closely spaced pits, apparently they collapsed into voids - lava tubes? The rille on the left side is also remarkable - it has short segments that join it at right angles. These are clearly tectonic in origin. And finally, the beautiful concentric crater in the midst of all this volcanic and tectonic activity seems to imply that volcanism is related to its formation. The presence of nearby craters of slightly larger and small diameters makes it unlikely that the inner donut formed by an impact's interaction with a buried layer.
Rükl plate 60'
Yesterday's LPOD: Wallology
Tomorrow's LPOD: Lighter Domes