Sen—Ceres’ peculiar bright spots continue to fascinate planetary scientists and now they have been studied in greater detail than ever by NASA’s Dawn probe.
Although no-one is yet certain what causes them, the Dawn team are now sure that they are highly reflective material on the dwarf planet’s surface. They could be patches of ice.
Dawn got its closest views yet of the mystery features on May 3 and 4, 2015, when the space probe imaged them from a distance of just 13,600 km (8,400 miles). The sequence of pictures has been combined to produce a short animation.
The close-up images allowed the mission team to tell that the brightest spots, inside a crater in Ceres’ northern hemisphere, are actually made up of several smaller spots. But what they are formed of is not at all clear.
Dawn’s principal investigator, Christopher Russell, of the University of California, Los Angeles, said in a statement: “Dawn scientists can now conclude that the intense brightness of these spots is due to the reflection of sunlight by highly reflective material on the surface, possibly ice.”
Apart from the new views of the strange spots, NASA’s new higher-resolution images also show the rest of the dwarf planet’s heavily cratered surface in greater detail. The science team will spend years poring over the many fascinating geological features revealed with a resolution of just 1.3 km (0.8 miles) per pixel.
Dawn, which entered orbit around Ceres on March 6, 2015, has completed its first mapping orbit of the world which lies in the asteroid belt between Mars and Jupiter. This took 15 days during which the spacecraft’s scientific instruments performed several observations. Now the probe is manoeuvring to get even closer to Ceres to study it in higher detail still.
It powered up its ion engines on May 9 to begin a month-long descent towards its second mapping orbit, which it will go into on June 6. It will then circle Ceres every three days at an altitude of 4,400 km (2,700 miles), which is three times closer than before. Known as the survey orbit, this will allow detailed mapping of the surface, allowing scientists to tell whether Ceres is still geologically active and more of the history of this dwarf planet. More images will be captured during the descent.
Dawn has already spent 14 months orbiting and studying another of the asteroids, Vesta, in 2011 and 2012 before heading for Ceres, powered by its three xenon ion electric engines. Vesta, which is about 525 km (326 miles) in diameter, is a very dry asteroid, but it is thought that Ceres, which formed later, may contain as much as 25 per cent water. Ceres, with a diameter of 950 km (590 miles) is the largest of the asteroids.
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