Occator’s bright spots are the most closely-studied so far. Initially
thought to show signatures of the salt hydrated magnesium sulphate,
more detailed analysis has now shown that the bright deposits are
dominated by sodium carbonate, ‘the most concentrated known
extra-terrestrial occurrence of carbonate on kilometre-wide scales in
the Solar System’. This is of great significance because such salts are like
those found in Earth’s hydrothermal environments. While they may have
been exposed by impacts at Ceres’ surface, they are likely to have
formed in its interior in a process involving liquid water, which would
suggest that it has, or had, a warmer internal temperature than previ-
ously supposed.
LITTLE WORLD, BIG SURPRISES!: Striking locally-bright areas are shown in this high resolution image of Ceres’ Occator Crater
taken from Dawn’s Low-Altitude Mapping Orbit (LAMO). Occator has a diameter of 92km (58 miles) and is 4km (2.5 miles)
deep. It has been of great interest since Dawn first imaged it on its approach to the dwarf planet in early 2015. Analysis of
Dawn’s VIR data indicates that these bright areas consist largely of sodium carbonate, a kind of salt found on Earth in hydro-
thermal environments. Occator seems to represent the highest concentration of carbonate minerals ever seen outside Earth.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
This raises a number of intriguing questions. Could there still possibly
be a remnant internal liquid water ocean beneath the layer of ice in
Ceres’ interior? Or was the water present 80 million years ago when the
impact occurred which created Occator? Was it the impact which
created the water through melting of Ceres’ mantle, generating the
heat to drive hydrothermal processes for a while. The apparent degree
of internal activity detected at Pluto was a big surprise, and such activ-
ity at Ceres is equally unexpected. It is hoped that more detailed analy-
sis of the composition of salts on the dwarf planet’s surface will be able
to tell us more about conditions deep within it.
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