Volcanoes

The Apollo missions that brought back rock Tsamples from the Moon enabled geologists to establish that the lunar circles, that are clearly visible from the Earth through a telescope, are basait extrusions. The presence of other volcanoes in the solar system was discovered by the Voyager 1 and 2 probes, including Mount Olympus on Mars, which is 24 km high and has a diameter of 500 km. It is the biggest volcano in the solar system.