Is there any idea how lunar craters size relate to the size of the meteorites which created them?

Reading this, it surprised me the amount of craters there are on the moon

There are at least 1.3 million craters larger than 1 km (0.62 mi) in diameter; of these, 83,000 are greater than 5 km (3 mi) in diameter, and 6,972 are greater than 20 km (12 mi) in diameter

Lunar Craters

I suppose the size of the meteorites which created them should be quite smaller than the size of the crater, because, otherwise, since the Earth must be exposed to the same amount of meteorites (more due to the larger size of Earth), even though we have an atmosphere that protect us, if the meteorites would be as big as the size of the lunar craters, we would be exposed to large meteorite catastrophes all the time.

Is there any idea how lunar craters size relate to the size of the meteorites which created them?

• Yes, researchers have used high-speed impacts (into sand in a vacuum) to understand crater formation. The size and shape of craters depend highly on speed and direction of impact, as well as size and mass of the impacting object. Commented Aug 4 at 10:10
• @TobySpeight can you mention a range of size of the crater in relation with the size of the meteorite? I'm pretty sure there is a minimum and maximum speed for meteorites, and the direction is also a limited set, so the result should be a limited set Commented Aug 4 at 15:20
• Sorry, I don't have numbers - my recollection is based on a TV documentary (possibly Walking Through Time). I'm pretty sure the experimental work was done at NASA's JPL, so you might be able to find something on the Web with that in your keywords. Commented Aug 4 at 16:18

2 Answers

Numerous scaling laws have been developed based on laboratory experiments, field experiments (e.g., TNT explosions), and computer models. There might be a more recent review, but the one by Johnson et al. (2016) is usually my go-to for the impactor-crater scaling laws (their equations 4 and 5 are slightly different, but close enough for most work).

To use them, you have to know the density of the target and body, diameter of the impactor, velocity of the impactor, surface gravity of the target, the simple-to-complex transition, and angle of impact. The simple-to-complex transition diameter is different for different bodies but is the approximate diameter below-which you get simple, bowl-shaped craters, and above-which you get complex craters with flat floors, central peaks, and/or wall terraces.

In the inner solar system, where rocky bodies are hit mostly by rocky asteroids, a very, very rough rule-of-thumb is you can tend to get craters very roughly 20 times the size of the impactor (e.g., Meteor or Barringer Crater in Arizona, roughly 1.2 km across, was probably formed by an iron-nickel meteorite 50 m in diameter). As I said in the previous paragraph, this depends on a lot of different parameters, so changing any of them will get you a different crater size without changing the actual size of the impactor. But, out where Pluto is, with more icy bodies striking each other at much slower speeds, the ratio is closer to a crater forms around twice the size of the impactor.

These scaling laws are still active areas of research, but at this point, the numbers are unlikely to change significantly with more data.

• As a very gratuitous side-note, I will add it's always nice to see myself cited in Wikipedia. That 1.3M crater number comes from my lunar crater database. Commented Aug 17 at 18:45

I would imagine the biggest variable in all this is the velocity of impact which would be determined by the source area of the impinging meteorite. If it was casually orbiting the moon for awhile and started spiralling in, I would imagine the impact crater wouldn't be as big or deep then say if it was a extra solar system piece of rock which would impact at a much greater speed.

• "casally orbiting the moon for awhile and started spiralling in" - That's not how gravity works. It's extremely difficult for a meteoroid in a solar orbit to to enter a lunar orbit, and if it did, there'd be no reason for it to spiral in. Pretty much all impacts are direct hits. Relative velocity is important, but the biggest variable is the asteroid's mass. Commented Aug 16 at 8:36
• Why would you "imagine" these things? Can you give some references to justify this? Commented Aug 16 at 20:54
• Hi Chenmuka. Its a figure of speech. Falls under sarcasm. It should be obvious that impact velocity would be related to crater size. Commented Aug 19 at 8:59