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CrustalTrudger t1_j3gkj64 wrote

They're impact craters. They occur, in varying sizes, on pretty much every solid body in the solar system but the number of preserved craters depends on the extent to which the surface of the body in question has been "resurfaced" (largely because cratering rates are much lower than earlier in the history of the solar system). Because of active plate tectonics and surface processes, Earth does not have many preserved impact craters, especially compared to the Moon, Mercury, etc, but there are a few well preserved ones, which are similarly quite circular.

Most craters are circular. There are elliptical craters (e.g., this example from Mercury), but they are relatively rare, accounting for only around 5% of craters (e.g., Bottke et al., 2000). Very specific conditions need to occur for an impact to generate an elliptical, as opposed to circular crater. One of the critical factors is the angle of impact, with shallow angles between the impact trajectory and the surface favoring ellpitical craters, but other conditions, like slow impact velocities, stronger target materials, and larger impactors, modulate what impact angle is able to produce an elliptical crater (e.g., Elbeshausen et al., 2013).

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BioTechproject t1_j3guhl5 wrote

And most importantly the reason why most craters are circular is because of the high impact velocities. The space rocks are so fast relative to eachother that angle doesn't usually matter, the rock simply detonates on impact. And like all explosions, the resulting crater is circular.

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daywalkker t1_j3he09f wrote

Just because something is round doesn't mean it is man-made. Planets are spherical or oblate spheroid and they surely aren't man-made. Man-made is not the only way to attain perfect, nearly perfect, or complex structures.

Hell, look at complex life on our planet. It is far more advanced than anything man has ever made and it is 100% natural.

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SierraPapaHotel t1_j3gv8tt wrote

As u/CrustalTrudger notes, they're just impact craters. The reason they are perfectly circular is due to energy dissipation. When an object impacts the surface, the energy of impact is spread out equally in every direction creating a circular crater. This happens regardless of the shape of the impacting object. And it's not just impact craters that are circular; if you look at pictures of explosion craters (from mortars or IEDs or volcanoes or whatever) the crater is circular for the same reasons.

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doc_nano t1_j3jiouu wrote

If you throw a rock very hard at some dry sand on a beach, it’ll make a disturbance in the sand. If you throw it hard enough, the disturbance in the sand will be a circle. The circular craters on the moon form for similar (though slightly different) reasons.

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