New research probes mystery of Ceres' bright spots
Two new studiespublished in the journal Nature have put forward fascinatingtheories on the origins of the dwarf planet Ceres, and the nature ofits enigmatic white spots. The studies drew on data collected byNASA's Dawn spacecraft as it continues its ongoing mission tocharacterize Ceres.
This week, Dawn reachedits third and final mapping orbit, with the probe flying a mere 240miles (385 km) above Ceres' desolate yet captivating surface. Thespacecraft's newly established orbit will allow it to capture imagesof Ceres with a resolution of 120 ft (35 m) per pixel.
One of the newlyreleased studies which was led by Andreas Nathues at the Max PlanckInstitute for Solar System Research, Göttingen, Germany, putsforward a theory on the composition of the roughly 130 white spotsthat pepper Ceres' surface.
It is widely believedthat the majority of the phenomenon are associated with impactcraters, the most prominent of which lies in the central depressionof the Occator crator, measuring some 6 miles (12 km) across. The newstudy, which uses data captured by Dawn's framing camera, suggeststhat the bright areas represent massive deposits of a magnesiumsulfate known as hexahydrite – a material that's fairly similar innature to Epson salts found back on Earth.
According to the team,the salt could be the the residue of instances where water-icesublimated in the distant past. Should the theory proveto be true, it could be treated as a marker for a subsurface layer ofbriny water-ice. This would explain the link between bright spots andimpact sites, as the force of an asteroid smashing into the surfaceof Ceres could have dug up the mixture, leaving it exposed fordetection by Dawn in the present day.
Beyond the suggestionthat salt is responsible for the bright spots, the researchhighlights images of Ceres' surface that appear to display a hazecovering the floor of the Occator crater. The phenomenon, which theteam suggest could represent the presence of water vapor, onlyappears around noon local time on Ceres and is reminiscent ofactivity observed on comets, whereby vapor temporarily lifts smallice and dust particles off the surface.
This would not be thefirst suggestion of such a phenomenon on Ceres. Back in 2014, ESA'sHerschel Space Telescope detected evidence of water vapor present in the dwarf planet's atmosphere with the use of its HIFIInstrument.
The second study,authored by members of the Dawn science team, looks beyond Ceressurface features, instead posing questions as to where and how thedwarf planet was created. The team behind the paper claim to havedetected the presence of ammonia-rich clays using Dawn's visible andinfrared mapping spectrometer.
"The presence ofammonia-bearing species suggests that Ceres is composed of materialaccreted in an environment where ammonia and nitrogen were abundant,"states Maria Cristina De Sanctis, lead author of the study, based atthe National Institute of Astrophysics, Rome. "Consequently, wethink that this material originated in the outer cold solar system."
According to theresearchers, it is possible that Ceres was formed farther out in thesolar system and was subsequently drawn inward, which would accountfor the presence of ammoniated compounds. Another theory holds thatthe dwarf planet could have been created relatively near its currentorbit, which lies between that of Mars and Jupiter, and may havelater incorporated ammonia-rich materials that had moved inward fromthe orbit of Neptune.
Scroll down to view a false color animation highlighting variations in Ceres' surface material.