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Dawn sees Ceres turn to reveal more surprises

Jenny Winder, News Writer
Feb 27, 2015, 4:41 UTC

Sen—NASA's Dawn spacecraft has observed the dwarf planet Ceres completing one full rotation and revealed that a mysterious bright spot, seen in previous images, has a dimmer companion.

The latest images were taken nearly 46,000 km (29,000 miles) from Ceres. Dawn observed the dwarf planet completing one revolution, which lasted about nine hours. The images show the full range of different crater shapes that can be found at Ceres' surface, from shallow, flat craters to those with peaks at their centres.

"Ceres' bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin. This may be pointing to a volcano-like origin of the spots, but we will have to wait for better resolution before we can make such geologic interpretations," Chris Russell, principal investigator for the Dawn mission, based at the University of California, said in a statement.

Russell told Sen, "These bright spots will not be resolved now for over a month as our trajectory will take us farther way from Ceres for awhile even though we are bound to its gravity. So we all will have to wait some time before we can solve the bright spot source problem."

"The brightest spot continues to be too small to resolve with our camera, but despite its size it is brighter than anything else on Ceres. This is truly unexpected and still a mystery to us," stated Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research in Germany.

Part of NASA’s Discovery Program, Dawn was launched in 2007. The mission's goal is to investigate in detail the two most massive bodies in the asteroid belt, which lies between Mars and Jupiter. There are profound differences in geology between the two protoplanets, Ceres and Vesta, though they formed and evolved relatively close to each other. 

Dawn has already visited the giant asteroid Vesta between 2011 and 2012, sending back over 30,000 images. Vesta has an average diameter of 525 km (326 miles) and appears to have a surface of basaltic rock. There may be ice a couple of metres below the surface which produced gullies, seen by Dawn, when impacts from space rocks melted the ice.

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This image of Ceres on Feb. 19 shows that the brightest spot on Ceres has a dimmer companion, which apparently lies in the same basin. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Ceres has an average diameter of 950 km (590 miles). It is believed to contain large quantities of ice and has a differentiated interior meaning that, like Earth, it has denser material at the core and lighter minerals near the surface.

Dawn's futuristic ion propulsion system will place Dawn in orbit around Ceres on March 6. Each of Dawn's three 30 cm diameter (12 inch) ion thrust units is movable in two axes to help control spacecraft attitude. Two ion propulsion engines are required to complete the mission, and the third engine serves as a spare.

Since launch the spacecraft has used each of the three ion engines, operating them one at a time. There are expected to be more than 2,000 days of thrust throughout entire the mission.

Over the next 16 months, scientists hope to to gain a deeper understanding of Ceres' origin and evolution by studying its surface. The bright spots and other interesting features will come into sharper focus, as they receive better and better views of the dwarf planet.