When near the horizon, the effects of 'twinkling' can give rise to amazing flashing colour effects which are often reported as peculiar objects, sometimes as UFOs. An active volcano, Maat Mons, was discovered on Venus by the Magellan spacecraft. Extinct volcanoes are seen on Mars. Two satellites are known to have active volcanoes, but these are very different from those on the Earth and on Venus. On Io, moon of Jupiter, there are active sulphur volcanoes and on Triton, a moon of Neptune, there are active volcanoes whose temperatures are far below zero centigrade.
Opinions differ as to whether there is evidence for extinct volcanoes on the Moon.
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