Extraterrestrial Calderas
Since the early 1960s, it has been known that volcanism has occurred on other planets and moons in the Solar System. Through the use of manned and unmanned spacecraft, volcanism has been discovered on Venus, Mars, the Moon, and Io, a satellite of Jupiter. None of these worlds have plate tectonics, which contributes approximately 60% of the Earth's volcanic activity (the other 40% is attributed to hot spot volcanism). Caldera structure is similar on all of these planetary bodies, though the size varies considerably. The average caldera diameter on Venus is 68 km. The average caldera diameter of Io is close to 40 km, and the mode is 6 km. Tvashtar Paterae is likely the largest caldera on Io with a diameter of 290 km. The average caldera diameter of Mars is 48 km, smaller than Venus. Calderas on Earth are the smallest of all planetary bodies and vary from 1.6 to 80 km as a maximum.
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