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Now that very high resolution imagery of the Moon's whole north, above 60 °N, can be viewed on one giant awesome zoomable map, I've been taking a close look at a number of craters. Anaxagoras sticks out to me as odd. Here is a photo of the width of the crater, roughly 45 km across, from the gigapan site linked above:

floor of Anaxagoras crater showing mountains, ridges, and collapsing walls

And here are images of a couple of details, the top one taking in an area about 5 km wide, the bottom one about 12 km:

sinuous gullies in crater wall

impact melt field full of cracks and ripples, ejecta on hills

And a topographic image, where the red areas are about 5 km higher than the pink areas:

topographic map of Anaxagoras crater

From the sharp lines of the crater wall, I've gathered that this crater is young. Also because rays of ejecta extend from it, though not of bright material like Tycho. Those rays are a bit more visible in the LMMP version of this same map.

These are my confusions:

  • Why are there mountains over the entire floor of the crater, not just in the center like usual? Associated with that, how can there be such large ridges on the south-west wall of the crater?

  • How can all the hills and mountains be covered by gigantic boulders (one pixel is about 2 m so a lot of those boulders have got to be 30 m across), while the melt plains have almost none? Wasn't it the impact that produced both the boulders and the melt?


Notes: Because this crater is so close to the north pole, the sun here is casting long shadows that fall to the north of everything, making it look lit from below.

All data is from the Lunar Reconnaissance Orbiter, which can also be explored at the Lunar Orbital Data Explorer site, as well as at the sites linked above.

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    $\begingroup$ You might point out that the images are lit from below, which is just unusual enough that it can take some active concentration to see the relief correctly rather than thinking it's inverted. :) $\endgroup$ Commented Jun 26, 2015 at 1:04
  • $\begingroup$ Here's that same zoomable map from the first three images in the question that's centered on Anaxagoras (73.48°N 10.17°W). The topographic image was made with Planetary Data System Geosciences Node Lunar Orbiter Data Explorer using LRO LOLA Topography (altimetry data) + Lunar Orbiter Global Digital Mosaic (morphologic map). $\endgroup$
    – TildalWave
    Commented Jun 26, 2015 at 1:47
  • $\begingroup$ @ypercubeᵀᴹ No, now that I check again. It's about 5 km deep, which is what one would expect. $\endgroup$
    – kim holder
    Commented Oct 31, 2021 at 18:22

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There have been a few internet post about the Anaxagoras Crater, on the Moon.

Regarding the central peaks, the floor of the crater has "a section of the anorthositic central peak complex". Anorthosite is a light colored mineral, mainly composed of plagioclase feldspar. It is the mineral that the Genesis Rock, collected by the Apollo 15 mission is composed of. Anorthosite is of interest to geologists because it is the mineral that formed the primordial crust of the Moon.

Additionally,

The crater floor is covered in relatively smooth impact melt; the melt ... has degraded over time and is now covered by an upper regolith layer and displays numerous younger small impact craters. Sections of the central uplift protrude above the crater floor melt and are covered with large boulders.

One of the smaller mounds,

is covered with large boulders, up to 30 meters (90 feet) across. Since the boulders cluster on top of topographic highs and are rare on the surrounding flat surfaces, they most likely were not thrown in from afar but rather are eroding out of the substrate.

A later post, from 2017, has alternate explanation,

Much of the impact melt on the floor of Anaxagoras is smooth, but there are some places with cracks or negative-relief features. These cracks and pit-like features probably formed during cooling of the melt as the material fractured, similar to the way scientists think the natural bridge in the King crater melt sheet formed. We simply do not know for certain. Additionally, there are several hills and bulges that are covered with clusters of boulders. There are no impacts in the melt sheet that might account for the boulder clusters, thus a possible explanation is that the boulders are eroding out of the impact melt that covers these hills. These boulders look similar to boulder clusters eroding out of wrinkle ridges in the mare; are they the result of a similar process? This observation suggests that perhaps erosion proceeds preferentially on the steeper slopes of bulges in the melt sheet and ridge crests of wrinkle ridges to produce boulder clusters. But why are boulders only eroding from these bulges? There are other steep slopes nearby, but these slopes do not have boulders.

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