rock-falls still in evidence, which have not been obliterated by long-
term processes like erosion by micrometeorites.
Ahuna Mons’ recent volcanism on an isolated dwarf planet is a sur-
prise, as usually only planets, or satellites orbiting around them, have
volcanism. Ceres has certainly provided us with many surprises so far
and there are no doubt more to come. One of them, the discovery of
ammonia-rich materials, may lead to planetary scientists having to re-
think our ideas on the dwarf planet’s very origins and formation.
Artist concept showing NASA’s Dawn spacecraft firing its ion thrusters above dwarf planet Ceres,. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
What is the origin of Ceres?
Ceres is possibly a remnant proto-planet, like Vesta a survivor from
the violent planet-building processes of the early Solar System 4.57 bil-
lion years ago, if different in its composition. However, the presence of
ammonia-rich clays on Ceres’ surface raises the question as to where
and how exactly it originated. Ceres appears to be a transition world,
neither totally rocky, nor an ice world. But, while it is close to the so-
called ‘frost-line’ in the Solar System, it’s not in a cold enough region for
such ammonia-bearing materials to form. So, did it form where it is, and
accumulate ammonia-rich material which migrated inwards from the
early outer Solar System? Or, did Ceres form in the vicinity of Neptune
and then move inward when the migration of the giant planets was dis-
rupting these outer regions some 4 billion years ago, flinging most such
objects out to form the Kuiper Belt or even out of the Solar System alto-
gether? Hopefully, further detailed studies of the dwarf planet’s com-
position will give us information to help understand this better.
What now for Dawn?
After greatly surpassing its objectives at both Vesta and Ceres,
Dawn’s prime mission officially ended on 30th June 2016. Project of-
ficials had proposed a possible new goal for the spacecraft, another
main-belt asteroid, 145 Adeona. The possibility of an extended mission
to another body had been considered feasible because of sufficient
remaining xenon fuel for the ion engines, and also thanks to steps taken
since 2012 to conserve the spacecraft’s supply of hydrazine fuel, used
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