WATER ICE IN OXO CRATER: Oxo, only 10km (6 miles) wide, is the second-brightest feature on Ceres. Only Occator’s central area is brighter. Oxo is unique because of
the water ice signatures detected within it, and also the large “slump” in its crater rim (seen here at the top of the image), where a mass of material on its rim has col-
lapsed into it. It is shown here in perspective view, and the elevation has been exaggerated by a factor of two. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Bright spots and salts
Sublimation of water ice may be responsible for some of Ceres most
spectacular and unexpected features – bright spots or faculae, up to
4 times brighter than the average brightness of the surface. Already
observed from a distance by Dawn before its arrival, there are over 130
of these features, most of them located near impact craters. The bright-
est and most striking are those found in Occator, an 80-million year old
(fairly recent in geological terms) crater.
OCCATOR’S CENTRAL DOME:
Dawn’s close-up view of Occator’s central bright area reveals a
dome in a smooth-walled pit in the centre of the crater. Numer-
ous linear features and fractures criss-cross the top and flanks of
this dome. There are also prominent fractures around the dome,
and they are also associated with the smaller brigh t regions
found within the crater. It is suggested that briny ice might reach
the surface through these fractures – a form of cryovolcanism -
where it sublimates, leaving a residue of bright salty deposits.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
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