Ceres: The tiny world where volcanoes erupt ice
ASU scientist investigates how volcanic activity has reshaped the face of Ceres
Ahuna Mons is a volcano that rises 13,000 feet high and spreads 11 miles wide at its base. This would be impressive for a volcano on Earth. But Ahuna Mons stands on Ceres, a dwarf planet less than 600 miles wide that orbits the sun between Mars and Jupiter. Even stranger, Ahuna Mons isn't built from lava the way terrestrial volcanoes are — it's built from ice.
"Ahuna is the one true 'mountain' on Ceres," said David A. Williams, associate research professor in Arizona State University's School of Earth and Space Exploration. "After studying it closely, we interpret it as a dome raised by cryovolcanism."
Dawn's Framing Camera looks down on the fractured summit of Ahuna Mons, tallest mountain on dwarf planet Ceres. The cracks on top suggest Ahuna grew by inflation: Icy freezing water pushed up inside the mountain, making a dome. (This image and the following two have the same scale and orientation, and are taken from the Science paper linked in the text.)Photo courtesy of Dawn Science Team and NASA/JPL-Caltech/GSFC
Researchers draped a digital terrain model over a shaded image of Ahuna, placing contour lines at 100-meter (330-foot) elevation intervals. Key spot elevations are shown in meters.Photo courtesy of Dawn Science Team and NASA/JPL-Caltech/GSFC
The geological map of the major units at Ahuna Mons will be filled in with more details as scientists continue to study this small world shaped by icy volcanism.Photo courtesy of Dawn Science Team and NASA/JPL-Caltech/GSFC
Although volcanic-related features appear across the surface of Ceres, for scientists perhaps the most interesting aspect is what these features say about the interior of the dwarf world. Dawn observations suggest that Ceres has an outer shell that's not purely ice or rock, but rather a mixture of both.
Recently, Williams was involved in research that discovered that large impact craters are missing, presumably erased by internal heat, but smaller craters are preserved.
"This shows that Ceres' crust has a variable composition — it's weak at large scales but strong at smaller scales," he said. "It has also evolved geologically."
In the big picture, said Williams, "Ceres appears differentiated internally, with a core and a complex crust made of 30 to 40 percent water ice mixed with silicate rock and salts." And perhaps pockets of brine still exist in its interior.
"We need to continue studying the data to better understand the interior structure of Ceres," said Williams.
Ceres is the second port of call for the Dawn mission, which was launched in 2007 and visited another asteroid, Vesta, from 2011 to 2012. The spacecraft arrived at Ceres in March 2015. It carries a suite of cameras, spectrometers and gamma-ray and neutron detectors. These were built to image, map and measure the shape and surface materials of Ceres, and they collect information to help scientists understand the history of these small worlds and what they can tell us of the solar system's birth.
NASA plans for Dawn to continue orbiting Ceres and collecting data for another year or so. The dwarf planet is slowly moving toward its closest approach to the sun, called perihelion, which will come in April 2018. Scientists expect that the growing solar warmth will produce some detectable changes in Ceres' surface or maybe even trigger volcanic activity.
"We hope that by observing Ceres as it approaches perihelion, we might observe some active venting. This would be an ideal way to end the mission," said Williams.