In two new studies, published today in the journal Nature, the dwarf planet Ceres reveals some of its most eye-catching secrets. In the first study, researchers identify the bright material that is causing Ceres’ mysterious spots as hydrated magnesium sulfates. The second study suggests the detection of ammonia-rich clays, raising questions about how the dwarf planet formed.
This false-color image shows the dwarf planet Ceres. Scientists use false color to examine differences in surface materials. The color blue on Ceres is generally associated with bright material, found in more than 130 locations, and seems to be consistent with salts. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.
Ceres has more than 130 bright areas, and most of them are associated with impact craters.
These unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material, although other compositions are possible, according to Dr Andreas Nathues of the Max Planck Institute for Solar System Research in Germany, who is the lead author on the first Nature study.
“These salt-rich areas were left behind when water-ice sublimated in the past. Impacts from asteroids would have unearthed the mixture of ice and salt,” Dr Nathues and co-authors said.
“The global nature of Ceres’ bright spots suggests that this world has a subsurface layer that contains briny water-ice.”
The brightest material on the dwarf planet is found in the inner portion of a crater called Occator. Some images of this crater show a diffuse haze near the surface that fills the crater’s floor.
“This may be associated with observations of water vapor by NASA’s Herschel Space Observatory that were reported about a year ago,” the researchers said.
“The haze seems to be present in views during noon, local time, and absent at dawn and dusk.”
This suggests that the phenomenon resembles the activity at the surface of a comet, with water vapor lifting small particles of dust and residual ice.
“Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles may explain this haze,” Dr Nathues and his colleagues wrote in Nature.
Future data from NASA’s Dawn spacecraft may test this hypothesis and reveal clues about the process causing this activity.
Occator crater (center) appears to be among the youngest features on Ceres. Dawn mission scientists estimate its age to be about 78 million years old. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.
In the second study, a team of scientists led by Dr Maria Cristina De Sanctis of the National Institute of Astrophysics in Rome analyzed the composition of Ceres and found evidence for clay minerals called ammoniated phyllosilicates. They used data from Dawn’s visible and infrared mapping spectrometer.
The presence of ammoniated compounds raises the possibility that the dwarf planet did not originate in the main asteroid belt, where it currently resides, but instead might have formed in the outer Solar System. Another hypothesis is that Ceres formed close to its present position, incorporating materials that drifted in from the outer Solar System.
“Our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. Ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on Ceres during differentiation,” Dr De Sanctis and co-authors said.
“This suggests that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt.”
The study also shows that daytime surface temperatures on the surface of the dwarf planet span from minus 136 degrees to minus 28 degrees Fahrenheit (minus 93 to minus 33 degrees Celsius).
“The maximum temperatures were measured in the equatorial region. The temperatures at and near the equator are generally too high to support ice at the surface for a long time, study authors say, but data from Dawn’s next orbit will reveal more details,” the scientists said.
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A. Nathues et al. 2015. Sublimation in bright spots on (1) Ceres. Nature 528, 237-240; doi: 10.1038/nature15754
M. C. De Sanctis et al. 2015. Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres. Nature 528, 241-244; doi: 10.1038/nature16172
