I'm trying to estimate the depth of the soil around this 300 m crater about 150 m from the lip of Lalande crate on the Moon's equator. In the image below from the LRO's camera the sun's incidence angle is 65o (it is 25o above the horizon). This image shows the crater doesn't have a floor, the reglith was loose enough and deep enough to slump down and fill it in after the impact. At this shallow sun angle, the sun also reaches all of it. Based on that I guesstimate that on the darker side the crater has an incline of no more than maybe 15o. So the crater is about 35 to 40 m deep, and there is no sign it penetrates a layer of coarser or denser regolith.

small crater beside lalande crater on moon's equator taken by Lunar Reconnaissance Orbiter

Here it is in context of Lalande and with the sun a bit higher, in the area where it is shown. The image is a screenshot of the Quickmap service, you can go directly to the spot on the map with this link.

lip of lalande crater taken by Lunar Reconnaissance Orbiter

In that one I traced a ridge a couple hundred meters away from the lip which seems to indicate where denser or more consolidated material begins. I couldn't find the LROC image file for the right side where the small crater is, so I don't know the sun-incidence angle, but it looks like the sun was a little higher. The wall of Lalande is in deep shadow at that sun angle, so the slope there is at least that steep - something over about 30o, between the lip and that first ridge. So, the ridge is over 100 m below the crater lip.

Can it be concluded from this that the fine-grain, upper layer of regolith in this area near the lip of Lalande is over 100 m deep?

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    $\begingroup$ I wouldn't be so sure about "no sign it penetrates a layer of coarser or denser regolith." I wouldn't be surprised if it was a very standard crater older than the Lalande crater, and then thoroughly coated with Lalande ejecta. $\endgroup$ – SF. Nov 30 '15 at 20:00
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    $\begingroup$ @SF i asked a planetary scientist about that a while ago (but didn't get a chance to follow up, it was very quick). She said the energy involved in creating Lalande would have obliterated any crater that close. It has to be younger. Lalande is 24 km across, for a sense of the impact involved. $\endgroup$ – kim holder Nov 30 '15 at 20:04
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    $\begingroup$ I can't find any good resolution daytime and nighttime thermal images of the area to produce a thermal inertia map. But if you superimpose Clementine Color-Ratio (sadly, it doesn't align exactly, but it's close enough) you'll see that satellite craters in the region are about as young as Lalande (likely secondary impact craters) and there's more exposed iron rich basalt between them and towards Lalande. It seems young, but based on data I judge this with, it's rather inconclusive I'm afraid. $\endgroup$ – TildalWave Nov 30 '15 at 20:11
  • $\begingroup$ If you have good resolution visible images and metadata for them, mainly solar angle, you could estimate topmost layer depth by measuring area of bright boulders vs shadow they cast, compare that with area of known regolith depth and you could estimate how deep those boulders sank into it. That involves a lot of work tho. :( But hey, good news, basically if you see a lot of boulders laying about and they seem only half or less sunk in (e.g. if shadow around them curves inwards), then you know it's a young and shallow regolith region. That region you ask about certainly looks that way to me. $\endgroup$ – TildalWave Nov 30 '15 at 20:15
  • $\begingroup$ @TildalWave looking at that overlay, the spot corresponding to this crater is darker, though. There is a much fresher looking crater to the west of it that is the closest light spot. Yes, i have noticed that the boulders seem submerged rather a lot. But the big thing to me is that ridge inside the lip of Lalande. That gave me pause. Maybe there are shelves under it that have been covered over with dust... $\endgroup$ – kim holder Nov 30 '15 at 20:22

Using @TildalWave's suggested method of estimating the depth of the regolithe, I looked for boulders penetrating the surface layer. There are a couple of them:

enter image description here enter image description here enter image description here

Most notable however are the large (~10m) boulders towards the north rim of the crater. They seem to be located in a pretty shallow place, so I would say that the depth of the soil is no more than a few meters.

enter image description here

So close to the Lalande crater, the crater must have been created afterwards, making a "dusty" impact in the depositions from the much larger event that created Lalande.

I use the assumption that boulders must lay on solid rock. That may be horribily wrong.

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    $\begingroup$ If i follow you correctly, you are assuming the boulders are laying on a solid surface. There isn't any reason to assume that - they were likely created by the impact that created Lalande, being material that was thrown up by the blast and then came to rest next to it. They themselves could be sitting on regolith. If you look at the videos for the first case on lpi.usra.edu/exploration/training/resources/impact_cratering , the model shows that at the rim of the crater the ground is essentially folded over on itself, which would suggest the depth of the regolith is doubled by this. $\endgroup$ – kim holder Feb 5 '16 at 20:49

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