Rosaly Lopes spent five years carefully inspecting a churning landscape where molten rock spilled forth like the arced jets of a water fountain. Using data from an orbiting probe, she picked out eruptions across the fiery surface, eventually spotting 71 active volcanoes that no one had ever detected before.
“People used to joke with me, ‘Oh, you found another active volcano!’” Lopes told me. “‘You’re going to be in the Guinness World Book of Records’”—until one day, one of those offhand comments made its way to somebody who actually worked for Guinness World Records. Lopes ended up in the 2006 edition, recognized for discovering the most active volcanoes anywhere.
None of the volcanoes were on Earth, though. They were several hundred million miles away, on a moon of Jupiter called Io.
Today, Io is known as the most volcanically active place in the solar system. Other volcanic spots are scattered across our neighboring planets and moons, too, and probably countless more in other solar systems across the universe. Recently, NASA announced it would fund proposals for four new robotic missions, all headed for a close look at these kinds of worlds—Io, Venus, and Triton, a moon of Neptune.
Not long ago, Earth held the title for the most volcanic spot in the solar system. As a rule, volcanic activity indicates that a world is cooling off; after planets and moons form—an extreme and fiery process—they can spend billions of years ejecting heat from their interiors through cracks in the surface. Small bodies, like our moon, should go cold faster than others, and spurts on the surface can reveal the invisible contours of a world deep within. “Volcanism is like a window into the interior of the planet,” says Sue Smrekar, an astronomer at NASA’s Jet Propulsion Laboratory who is leading one of the proposed missions.