Washington — A geologic map of Jupiter's moon Io reveals some of the most unusual and active volcanoes ever documented in the solar system, according to a press release from the U.S. Geological Survey (USGS), which has published the map.

A group of scientists from Arizona State University produced the map, which shows a surface where volcanic activity occurs at 25 times the rate on Earth. Since discovery in 1610, Io has been the subject of observation, first by Earth-based telescopes and then by orbiting spacecraft. Over time, these studies revealed a celestial body greatly influenced by the gravitational forces of Jupiter, but also by its sister moons Europa and Ganymede.

These gravitational forces are so great they cause massive, rapid flexing of Io's surface and interior. The flexing generates tremendous heat in the moon's interior that finds its release in volcanic activity on the surface.

”It is exciting to have the reach of our science extend across 400 million miles to this volcanically active moon of Jupiter,” said USGS Director Marcia McNutt. “Somehow it makes the vast expanse of space seem less forbidding to know that similar geologic processes which have shaped our planet are active elsewhere.”

The highly detailed map reveals a number of volcanic features including volcanic domes and depressions, lava flow fields, mountains and plume deposits. Also interesting is what the map does not show. Unlike Earth, its moon and Mars, Io shows no signs of impact craters.

“Io has no impact craters,” said David Williams, who led the project from Arizona State University. “It is the only object in the solar system where we have not seen any impact craters, testifying to Io's very active volcanic resurfacing.”

The images that form the basis of the map were collected by a variety of NASA spacecraft over an extended period of time, including Voyager 1 and 2 in 1979, the Hubble Space Telescope from 1990 to the present, the Galileo spacecraft that orbited the Jovian system from 1996 to 2001 and the Cassini spacecraft, which did a Jupiter fly-by in December 2000 on the way to its primary mission at Saturn.

USGS has been studying the geology of other celestial bodies at its Astrogeology Science Center since the center was created in the early 1960s. The agency began producing planetary maps in support of the Apollo moon landings, and continues to help establish a framework for integrating and comparing past and future studies of extraterrestrial surfaces.

“Remotely characterizing the surfaces of planetary bodies forces scientists to carefully consider and test hypotheses that address the evolution of an entire planet,” said Ken Herkenhoff, acting director of the Astrogeology Science Center.