WASHINGTON: Scientists were of the view that they were places where impacts have excavated a briny layer of water-ice under the dwarf planet’s surface.
It has been the big Solar System mystery of 2015 – what are the bright spots on Ceres, the largest object in the asteroid belt between Mars and Jupiter?
The framing camera on the US space agency’s probe has catalogued some 130 spots on the 950km-wide world. But by far the most impressive collection is to be found in a crater dubbed Occator in Ceres’ northern hemisphere.
When the probe arrived at the dwarf, the camera settings were programmed to take account of what is generally a very dark surface – as black as asphalt. But this meant the super-bright depressions within Occator completely overwhelmed the instrument’s sensor.
“The reflectivity is in the order of 0.25, which means about 25% of the light is reflected; and in the inner core centre [of the Occator spot collection] it’s even more – up to 50-60% of the light is reflected; while the remaining surface is rather dark – the average is about 9%,” said the scientist from the Max Planck Institute for Solar System Research in Goettingen, Germany.
Subsequent investigation now indicates that there is likely a global layer of ice and salt under the rocky rubble that coats Ceres.
When a space impactor digs into this layer and exposes it, the ice starts to sublime (to turn directly from a solid to a gas). The released vapour then escapes away from the surface, lifting ice and dust particles in the process, to produce a kind of haze.
