Anomalously bright areas on the dwarf planet Ceres have the highest concentration of sodium carbonate ever seen outside our planet, says a new study published in the journal Nature.
Ceres’ bright spots are seen up close in this image from NASA’s Dawn spacecraft. The probe took this image on March 26, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 km) above the surface. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.
Ceres’ Occator crater is home to a cluster of bright spots. Named for the Roman deity of harrowing, the crater is about 78 million years old.
It has a diameter of 57 miles (92 km) and a depth of about 2.5 miles (4 km). Its walls are nearly vertical in some areas, although in others a large amount of material has slipped into its interior.
The new study, led by Dr. Maria Cristina De Sanctis from the National Institute of Astrophysics in Rome, Italy, finds that the dominant mineral of the bright areas is sodium carbonate, a kind of salt found on Earth in hydrothermal environments. This material appears to have come from inside the dwarf planet.
“This is the first time we see this kind of material elsewhere in the Solar System in such a large amount,” Dr. De Sanctis said.
The upwelling of this material suggests that temperatures inside Ceres are warmer than previously believed.
Impact of an asteroid on the dwarf planet may have helped bring this material up from below, but Dr. De Sanctis and her colleagues on NASA’s Dawn mission think an internal process played a role as well.
The results also suggest that liquid water may have existed beneath the surface of Ceres in recent geological time.
The salts could be remnants of an ocean, or localized bodies of water, that reached the surface and then froze millions of years ago.
“The minerals we have found at the Occator central bright area require alteration by water. Carbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator,” said Dr. De Sanctis, principal investigator of Dawn’s visible and infrared mapping spectrometer.
The center of Occator crater is the brightest area on Ceres. The inset perspective view is overlaid with data concerning the composition of this feature: red signifies a high abundance of carbonates, while gray indicates a low carbonate abundance. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.
Last year, the team reported that Ceres’ surface contains ammoniated phyllosilicates, or clays containing ammonia.
Because ammonia is abundant in the outer Solar System, this finding introduced the idea that Ceres may have formed near the orbit of Neptune and migrated inward. Alternatively, Ceres may have formed closer to its current position between Mars and Jupiter, but with material accumulated from the outer Solar System.
The new results also find ammonia-bearing salts — ammonium chloride and/or ammonium bicarbonate — in Occator crater.
The carbonate finding further reinforces Ceres’ connection with icy worlds in the outer Solar System.
NASA’s Dawn mission exceeded all expectations during its primary mission to Vesta and Ceres. Image credit: NASA / JPL-Caltech / Harmanx.
According to NASA, the Dawn space probe completed its primary mission on June 30, 2016.
The historic mission exceeded all expectations originally set for its exploration of the protoplanet Vesta and the dwarf planet Ceres.
The mission is the first to orbit two extraterrestrial solar system targets, and the first to orbit any object in the main asteroid belt.
Dawn has traveled 3.5 billion miles (5.6 billion km) since launch, and has made 2,450 orbits around Vesta and Ceres.
The spacecraft has returned about 69,000 images, combined, of both planetary bodies.
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M. C. De Sanctis et al. Bright carbonate deposits as evidence of aqueous alteration on (1) Ceres. Nature, published online June 29, 2016; doi: 10.1038/nature18290
