Ice Volcanoes and More: Dwarf Planet Ceres Continues to SurpriseThe dwarf planet Ceres is a complex and active world unlike any other place in the solar system, new research suggests.
Observations by NASA's Ceres-orbiting Dawn spacecraft indicate that "ice volcanos" have erupted on the dwarf planet in the recent past and that Ceres' crust is an odd ice-rock mixture that has never been observed before, scientists reported in a series of six new studies published online today (Sept. 1) in the journal Science.
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For example, the surface of Ceres is much more diverse and complex than that of Vesta, possessing extensive linear structures, lobed features caused by flowing material and a 2.5-mile-high (4 km) mountain (in addition to numerous craters).
This massif, known as Ahuna Mons, resembles the dome-shaped mountains created by volcanism here on Earth, researchers reported in one of the new studies. And Dawn team members said they think Ahuna Mons was indeed created by a volcano, but one that spewed out cold, molten ice rather than hot, liquid rock.
The researchers — led by Ottaviano Ruesch, of NASA's Goddard Space Flight Center in Greenbelt, Maryland — said they aren't sure exactly what Ceres' "cryomagma" is made of, but they suggested it could be a mix of chlorine salts and water ice.
Furthermore, Ahuna Mons appears to be quite young, the researchers said. Analyses of crater counts suggest that the mountain formed in the last 200 million years or so, study team members said. (Like the rest of the solar system, Ceres itself formed about 4.56 billion years ago.)
In another one of the new studies, a team led by Debra Buczkowski,,of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, identified other dome-shaped features that also appear to be products of cryovolcanism (though not all of it as recent as the activity responsible for Ahuna Mons). Buczkowski and her colleagues also concluded that some of Ceres' linear features likely represent subsurface faults.
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Before Dawn got to Ceres, most astronomers thought the dwarf planet's crust consists primarily of water ice. But another one of the new Science studies, which is based on a detailed analysis of Ceres' many craters, suggested that's not the case.
Water ice is fairly soft, at least compared to rock. So if Ceres had a primarily icy shell, the dwarf planet's craters would tend to "relax," or flatten out, on relatively short timescales: 10 million to 100 million years or so, the researchers said. But study leader Harald Hiesinger, of the University of Munster in Germany, and his colleagues didn't find the expected relaxation.
Instead, Ceres' crater morphology suggests that the dwarf planet's crust is a strange mix of perhaps 60 percent rock and 40 percent ice, Russell said.
"This is something that we haven't seen before," he said.
"It's a new material to us — something that, if you hit it really hard, it will melt and flow, but you don't have to warm it up to the temperature of lava," Russell added. "We have many, many different areas where the material has flowed across the surface after having been hit by perhaps a meteorite or something of that nature."
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Another of the new studies, this one led by Russell, suggested that Ceres may possess a thin atmosphere; such an "exosphere" could explain Dawn's observations of the solar wind interacting with the dwarf planet, the researchers wrote.
One of the other Science papers reported the probable detection of water ice, likely unearthed by an impact or landslide, at the bottom of a crater named Oxo. Another paper concluded that Ceres' surface was likely substantially altered by water at some point in the past, based on the widespread distribution of clay minerals (which only form in water).
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Much more, including pics and video, at the source: http://www.space.com/33934-dwarf-planet-ceres-ice-volcano-discoveries.html
