There She Blows... Ice--and how!(SCIENCE & TECHNOLOGY) (cryovolcanism on dwarf planet Ceres)

• Author: Bhaffman-Miller, Judjth

THE DWARF PLANET Ceres is the largest worldlet inhabiting our solar system's Main Asteroid Belt, where a myriad of small, rocky, icy, and metallic objects jitterbug around the sun between the orbits of two major planets: Mars and Jupiter. Ceres is large enough to have had the pull of its own relentless gravity mold it into a spherical shape. Planetary scientists have announced that they have unlocked one of the secrets long held by this small world. Ahuna Mons, a volcano on Ceres, was found not to have been built from lava the way that Earth's volcanoes are constructed: it instead is made of ice.

Ahuna Mons rises 13,000 feet, and is 11 miles wide at its base. This certainly would be an impressively large volcano on our own planet, but Ceres is less than 600 miles wide. 'Ahuna is one true 'mountain' on Ceres. After studying it closely, we interpret it as a dome raised by cryovolcanism," explains David A. Williams, associate research professor in Arizona State University's School of Earth and Space Exploration.

Cryovolcanism is a form of low temperature volcanic activity, where molten water ice--usually combined with ammonia or salts--plays the same role as molten silicate rock erupted from Earth's familiar volcanoes. The giant ice-mountain Ahuna Mons is a volcanic dome constructed by repeated eruptions of freezing salty water.

Williams is a member of a team of planetary scientists working with NASA's Dawn mission. His specialty is volcanism. "Ahuna is truly unique, being the only mountain of its kind on Ceres. It shows nothing to indicate a tectonic formation, so that led us to consider cryovolcanism as a method of its origin."

The Dawn spacecraft is a probe launched in 2007. Its mission is to study the two most-massive inhabitants of the Main Asteroid Belt--the dwarf planet Ceres, and the somewhat smaller asteroid, Vesta. A dwarf planet like Ceres is defined as a solar system denizen that is smaller than a major planet, but larger than an asteroid--and astronomers have understood for decades that Ceres is the largest inhabitant of the Main Asteroid Belt.

In 2006, the International Astronomical Union classified Ceres as a dwarf planet, rather than an asteroid, because of its size. Even though Vesta is the second-largest body in the Main Asteroid Belt, it still is small enough not to have been molded into a sphere by the pull of its own gravity, and it has retained its status as an asteroid.

NASA's Jet Propulsion Laboratory in Pasadena...