Dawn continues to unravel Ceres' secrets

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Composite image of Ceres' Occator crater(Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)

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Dawn's science team has presented a treasure trove of data and images captured by the spacecraft as it orbits a mere 240 miles (385 km) above the surface of the dwarf planet Ceres. The observations, which include a stunningly detailed view of the famous Occator crater, are leading to a series of breakthroughs regarding the nature of the enigmatic wanderer including the first detection of ice water on the planetoid's surface.

As always, we'll begin with the Occator crater. Spanning an impressive 57 miles (92 km), the impact site is believed to be among the youngest of the large craters scarring the surface of Ceres, with astronomers estimating its age at 80 million years. The composite image displays in fine detail a gentle dome in the white covered centre of the crater within a walled pit, and well as a host of fractures lining the basin of the feature.

The fractures are believed to be the hallmarks of recent geological activity. Naturally, the image is dominated by the bright blemishes of what is now believed to be a kind of salt, not far removed from epsom salts found here on Earth, which shine in stark contrast to their dull surroundings.

Much of the data returned by Dawn hints at a subsurface layer of ice and volatile materials. A color-enhanced map of Ceres contained in the new release, highlights the distribution of impact sites and the surprising diversity of surface materials.

An enhanced color elliptical map of Ceres – the image boasts a resolution of 460 ft (140 m) per pixel, and includes infrared wavelengths of light ordinarily invisible to the naked eye(Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Most interestingly, Dawn's science team has observed certain color variations that are believed to occur as a result of surface impacts dredging up a subsurface layer of ice and volatile materials. The team believe that the surface composition surrounding some impact sites, such as the Haulani crater, may have further altered the properties of the exhumed materials.

Further evidence for the existence of a subsurface layer of ice, which had been one of the leading theory accounting for the existence of bright deposits on Ceres surface was provided by Dawn's Gamma Ray and Neuron Detector (GRaND) instrument.

GRaND was designed to map the interaction between cosmic rays and the dwarf planet's desolate surface in order to divine the chemical make-up of Ceres' uppermost meter of regolith. Upon analyzing the data collected by GRaND, the team discovered that whilst there was an abundance of neutrons at the dwarf planet's equator, the population of the subatomic particles at the polls was comparatively scarce.

Map of Ceres displaying the distribution of hydrogen, represented in blue, and neutrons, which are represented in red(Credit: NASA/JPL-Caltech/UCLA/ASI/INAF)

According to the team, this imbalance suggests the presence of significant quantities of hydrogen located below the surface near Ceres' polar regions. As hydrogen accounts for two of the three molecules that make up H2O, the team are considering this a positive indicator for the presence of water ice buried below the surface.

While GRaND hunted for oblique evidence of a buried layer of water ice, Dawn's visible and infrared mapping spectrometer (VIR) made the first detection of water on Ceres' surface. The signature was detected in a 6 mile (9 km)-wide impact site known as Oxo crater, which is located in Ceres' northern hemisphere. Oxo represents the second brightest feature present on Ceres' surface, with the Occator crater remaining the brightest.

It is thought that the water was uncovered either due to the impact or thanks to a more recent landslide, and it is not yet known whether the water exists in ice form or if it is bound in minerals.

Source: NASA

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