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Was taking some extremely amatuer pictures of the moon from my cheap telescope with my camera phone...

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You see the crater Im talking about? Top right.The one with a little nub in the middle- which Im sure is actually massive. How was this formed differently than the other craters? What couldve caused the hill?

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Nice picture! Those peaks are actually a very common feature in craters formed by large impacts. Craters with these features are known as "complex craters". Basically what happens is that when the meteor hits, it pushes in the surface. Then the underlying mantle produces an "elastic rebound" and pushes outwards. This is a similar effect to what happens when you hit a drum. Your drumstick rebounds off the drum, and the drum begins to vibrate. Since rock (even molten rock) is much more dense than a drumskin, it does not vibrate very much. The vibrations solidify, resulting in a crater with one central peak.

How exactly this happens is still being investigated. This paper provides a pretty good explanation of what happens, but it's quite technical.

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Even larger impacts will produce ring structures. These are relatively rare on the Earth, since such structures are quickly weathered away. A good example of this is the Chicxulub crater off the Yucatan peninsula (the impact that killed the dinosaurs).

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  • $\begingroup$ Thanks for the extremely comprehensive answer. Is there a certain size class of asteroid where these would be more common? I dont usually see these on the smaller craters- assuming because it sidnt get deep enough to deform the required mantle layer? So I guess the question would be how thick is the crust usually on the moon? $\endgroup$ – Magic Octopus Urn Sep 30 '18 at 5:04
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    $\begingroup$ @MagicOctopusUrn Unfortunately, I do not know what the cutoff is. But I know that it depends on both the size of the impactor and the structure of the crust and mantle. A more fluid crust and mantle would be more elastic, and a larger impactor would provide more energy. $\endgroup$ – Phiteros Sep 30 '18 at 5:17
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    $\begingroup$ Haha given the bumpy and chaotic gravitational field of the moon knowing the average crust depth would be a chore Im sure- thanks for the clarification regardless. $\endgroup$ – Magic Octopus Urn Sep 30 '18 at 5:24
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That is the rebound effect. Just like a rock falling into a pond causes a big ripple and a big drop to jump out in the center, the same happens with a rock striking the Moon.

Refer to this astrophysics stackexchange for more information.

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    $\begingroup$ Great analogy but rofl that name dude- planning any trips to Uranus to destroy it too? $\endgroup$ – Magic Octopus Urn Sep 30 '18 at 5:25
  • $\begingroup$ @MagicOctopusUrn best. lmaoing. comment. ever. $\endgroup$ – Helen Sep 30 '18 at 8:40

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