· Mars also has many distinctively volcanic features, including the largest volcano in the solar system, Olympus Mons, which towers 16 miles high over the Martian landscape. "If volcanism had occurred up until the last 1% of geologic time, it is very unlikely to have stopped," McEwen says. "We just haven't observed anything that is a smoking gun on either Mars or Venus.”
· Volcanoes also shaped Mercury. There, however, the activity appears to have stopped operating early in the planet's history, billions of years ago. On our moon, too, volcanism operated early and then shut off sometime around 3 billion years ago.