Does the material that hits the moon all vaporize and disperse so much it doesn't lead to enriched deposit areas, or could it sometimes be useful?
I'm thinking in particular of a permanent moon base, the beginnings of a moon economy.
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asked Sep 17, 2014 at 22:06
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$\begingroup$ Well... the same materials fall on earth, don't they? We can just mine them here. $\endgroup$– Rikki-Tikki-TaviSep 18, 2014 at 10:20
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$\begingroup$ Yes, but they should be more concentrated on the Moon, without an atmosphere to speak of. $\endgroup$– PearsonArtPhoto ♦Sep 18, 2014 at 14:08
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$\begingroup$ And more concentrated could be especially useful on the moon, if it made enough difference. Getting your iron from meteor leftovers could be a lot cheaper than shipping it from Earth, couldn't it? I especially wonder about meteors with high water content. I read a meteor 10 m wide hits the moon about once every 10 to 40 years. If such a meteor hit the moon 20 years ago could a significant amount of the water be recoverable? $\endgroup$– kim holderSep 18, 2014 at 14:36
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Dennis Wingo and I had an argument over this. Wingo argues asteroid impacts have left rich ore deposits on the moon. My response (which he did not like) was citing Barringer's disastrous effort to mine Barringer Crater in Arizona. Barringer was correct that the impactor was metallic. But the impact scattered the ore far and wide leaving it too diluted to be profitably mined.
Dennis pointed to intact metallic meteorites found on earth's surface as well as Mars surface. He argued meteorites hit the moon slower than Mars and Earth due to the moon's shallower gravity well. I replied that the planet's atmosphere slowed the impactors so they only hit at terminal velocity. Of course the moon doesn't have enough atmosphere to slow down meteorites.
I made a chart of speeds at which asteroids would strike the moon:
An explanation of how I built the above histogram can be found at my blog post One Legged Stools.
Very large meteorites have a higher mass/(cross section surface area ratio) and thus a faster terminal speed. So it might be possible big impactors like the Sudbury meteorite hit the earth faster than the slowest speeds in the above histogram.
Here is an article speculating the lunar magnetic anomalies are metallic deposits left by impacts. If so, we have a pretty good idea of locations of Sudbury like deposits on the moon.
So I am coming around to Wingo's opinion that there are rich lunar metal deposits left by impactors.
Does this mean they can be profitably mined? No. The delta V from earth's surface to the moon and back is around 20 km/s. Transportation expense prevents profitable platinum or gold mining. Even deposits of pure lunar crack cocaine would be a money pit.
To profitably mine extra-terrestrial metals, we need to break the tyranny of the rocket equation. Extra terrestrial propellent might do that. So I would argue the most valuable lunar commodity won't be gold or platinum. It will be water. Water might be found in the cold traps at the lunar poles. And it is thought that the lunar water at the cold traps is exogenic in origin. Some of the volatile gasses from cometary or asteroidal impacts will find their way to the 40 Kelvin lunar cold traps, freeze and stay. Thus it's possible rich water and volatile deposits have accumulated over the eons in spite of being widely dispersed.
So my answer to your question is a tentative yes. Yes, it's possible meteorites have left useful deposits on the moon's surface.
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$\begingroup$ In the eventual situation of using those deposits on the moon itself, though, presumably those impactor sites could be valuable. Awesome chart, btw. $\endgroup$ Sep 18, 2014 at 15:50
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$\begingroup$ The y axis is number of objects per year? $\endgroup$ Sep 18, 2014 at 15:52
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1$\begingroup$ Brilliant, these are exactly my thoughts on the matter too. That lunar north pole contains ice water embedded into its permanently shadowed regolith is the most valuable resource one can find there regardless of what else from it one might want to bring back to Earth. It's simply too expensive to deliver to the Moon in industrial quantities yet indispensable to most industrial ISRU processes (or, say, to store energy in the form of Hydrogen and Oxygen by electrolysis of water to be later used during long lunar nights). $\endgroup$ Sep 18, 2014 at 15:54
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1$\begingroup$ @briligg No, the y axis is how many impacts if every known impactor (as of July 2013) hit the moon. A few would hit at 3 km/s. Most would hit 8 to 18 km/s. A small fraction would hit at 42 km/s. The graph is intend to show what fractions of impactors might hit at a certain speed, not impacts per year. $\endgroup$– HopDavidSep 18, 2014 at 16:10
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1$\begingroup$ @briligg For the rate of (and energy released during) impacts I suggest you look-up Passive Seismic Experiment data for shallow moonquakes. There ought to be some charts out there, I've seen them included in various presentation slides. Identifying exact cause is not as straight-forward as one might imagine though, some of the shallow epicenter moonquakes of shorter duration might be attributed to collapsing lava tubes, landslides and similar. Most non-shallow impact angle ones do have a distinct signature tho. $\endgroup$ Sep 18, 2014 at 16:30