Two new studies published in the journal Nature have put forward fascinating theories on the origins of the dwarf planet Ceres, and the nature of its enigmatic white spots. The studies drew on data collected by NASA's Dawn spacecraft as it continues its ongoing mission to characterize Ceres.
This week, Dawn reached its third and final mapping orbit, with the probe flying a mere 240 miles (385 km) above Ceres' desolate yet captivating surface. The spacecraft's newly established orbit will allow it to capture images of Ceres with a resolution of 120 ft (35 m) per pixel.
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One of the newly released studies which was led by Andreas Nathues at the Max Planck Institute for Solar System Research, Göttingen, Germany, puts forward a theory on the composition of the roughly 130 white spots that pepper Ceres' surface.
It is widely believed that the majority of the phenomenon are associated with impact craters, the most prominent of which lies in the central depression of the Occator crator, measuring some 6 miles (12 km) across. The new study, which uses data captured by Dawn's framing camera, suggests that the bright areas represent massive deposits of a magnesium sulfate known as hexahydrite – a material that's fairly similar in nature to Epson salts found back on Earth.
According to the team, the salt could be the the residue of instances where water-ice sublimated in the distant past. Should the theory prove to be true, it could be treated as a marker for a subsurface layer of briny water-ice. This would explain the link between bright spots and impact sites, as the force of an asteroid smashing into the surface of Ceres could have dug up the mixture, leaving it exposed for detection by Dawn in the present day.
Beyond the suggestion that salt is responsible for the bright spots, the research highlights images of Ceres' surface that appear to display a haze covering the floor of the Occator crater. The phenomenon, which the team suggest could represent the presence of water vapor, only appears around noon local time on Ceres and is reminiscent of activity observed on comets, whereby vapor temporarily lifts small ice and dust particles off the surface.
This would not be the first suggestion of such a phenomenon on Ceres. Back in 2014, ESA's Herschel Space Telescope detected evidence of water vapor present in the dwarf planet's atmosphere with the use of its HIFI Instrument.
The second study, authored by members of the Dawn science team, looks beyond Ceres surface features, instead posing questions as to where and how the dwarf planet was created. The team behind the paper claim to have detected the presence of ammonia-rich clays using Dawn's visible and infrared mapping spectrometer.
"The presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant," states Maria Cristina De Sanctis, lead author of the study, based at the National Institute of Astrophysics, Rome. "Consequently, we think that this material originated in the outer cold solar system."
According to the researchers, it is possible that Ceres was formed farther out in the solar system and was subsequently drawn inward, which would account for the presence of ammoniated compounds. Another theory holds that the dwarf planet could have been created relatively near its current orbit, which lies between that of Mars and Jupiter, and may have later incorporated ammonia-rich materials that had moved inward from the orbit of Neptune.
Scroll down to view a false color animation highlighting variations in Ceres' surface material.