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Body Crater Diameter
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1. Mercury Caloris Basin 1,550 km (963 mi)
2. Mercury Rembrandt 715 km (444 mi)
3. Venus Mead 280 km (170 mi)
4. Earth Vredefort 250–300 km (160–190 mi)
5. Moon Procellarum Basin 3,000 km (1,900 mi) Not confirmed as an impact basin.
6. Moon South Pole–Aitken basin 2,500 km (1,600 mi)
7. Moon Mare Imbrium 1,145 km (711 mi)
8. Mars North Polar Basin 10,600 × 8,500 km (6,550 × 5,250 mi) Not confirmed as an impact basin
9. Mars Hellas Planitia 2,300 km (1,400 mi)
10.Mars Utopia Planitia 3,300 km (2,100 mi)
11. Vesta Rheasilvia 505 km (310 mi)
12. Vesta Veneneia 395 km (250 mi)
13. Ganymede (Jupiter) Epigeus 343 km (213 mi)
14. Callisto (Jupiter) Valhalla 360 km (224 mi)
15. Callisto (Jupiter) Heimdall 210 km (130 mi)
16. Mimas (Saturn) Herschel 139 km (86 mi)
17. Tethys (Saturn) Odysseus 445 km (277 mi)
18. Dione (Saturn) Evander 350 km (220 mi)
19. Rhea (Saturn) Mamaldi 480 km (300 mi)
20. Rhea (Saturn) Tirawa 360 km (220 mi)
21. Titan (Saturn) Menrva 392 km (244 mi)
22. Iapetus (Saturn) Turgis 580 km (360 mi)
23. Iapetus (Saturn) Engelier 504 km (313 mi)
24. Iapetus (Saturn) Gerin 445 km (277 mi)
25. Iapetus (Saturn) Falsaron 424 km (263 mi)
26. Titania (Uranus) Gertrude 326 km (203 mi)
Source:
http://en.wikipedia.org/wiki/List_of_largest_craters_in_the_Solar_System
An impact crater is an approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the hypervelocity impact of a smaller body with the surface. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins. Meteor Crater is perhaps the best-known example of a small impact crater on the Earth.
Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids. On other planets and moons that experience more active surface geological processes, such as Earth, Venus, Mars, Europa, Io and Titan, visible impact craters are less common because they become eroded, buried or transformed by tectonics over time. Where such processes have destroyed most of the original crater topography, the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.
The cratering records of very old surfaces, such as Mercury, the Moon, and the southern highlands of Mars, record a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. Since that time, the rate of crater production on Earth has been considerably lower, but it is appreciable nonetheless; Earth experiences from one to three impacts large enough to produce a 20 km diameter crater about once every million years on average. This indicates that there should be far more relatively young craters on the planet than have been discovered so far. The cratering rate in the inner solar system fluctuates as a consequence of collisions in the asteroid belt that create a family of fragments that are often sent cascading into the inner solar system. Formed in a collision 160 million years ago, the Baptistina family of asteroids is thought to have caused a large spike in the impact rate, perhaps causing the Chicxulub impact that may have triggered the extinction of the dinosaurs 66 million years ago. Note that the rate of impact cratering in the outer Solar System could be different from the inner Solar Syste