ARRIVING AT A NEW WORLD : NASA ’ s Dawn probe captured this view of dwarf planet Ceres ’ northern regions on 14th and 15th April , 2015 , shortly after its arrival , from a distance of about 22,500 kilometres ( 14,000 miles ). Credit : NASA / JPL-Caltech / UCLA / MPS / DLR / IDA
and versatile ion propulsion system were discussed in Issue # 10 of ‘ RocketSTEM ’ (‘ Journey to the Beginning of the Solar System ’, February 2015 ), as were the results of the first phase of its mission at asteroid 4 Vesta . Since then , it has continued its journey on to dwarf planet Ceres , which it has been orbiting since March 2015 . Here we provide a summary of what Dawn has revealed so far about this small but significant world , described by Dr . Rayman before the encounter as ‘ an intriguing and mysterious orb that has beckoned for more than two centuries ’ since its discovery by Giuseppe Piazzi on 1st January 1801 .
Why was Ceres a significant target ?
Ceres , like Vesta , was chosen for study by the Dawn mission because it is thought to hold keys to unlocking the secrets of the Solar System ’ s early history . This has , indeed , proved to be the case for Dawn ’ s first target , Vesta , which was confirmed by the spacecraft to be one of the last remaining rocky proto-planets , a remnant building-block of the kind that formed the terrestrial planets , and the only known asteroid with an Earth-like differentiated internal structure of core , mantle , and crust .
As for Ceres , much of its attraction as a target for scientists was the fact that it is an ‘ oddball ’ of the asteroid belt . Thought at its discovery in 1801 to be a comet , then considered a planet , it was finally re-designated an asteroid in the 1850s when increasing numbers of small bodies were discovered orbiting the Sun between Mars and Jupiter . However , with an average diameter of 945km ( 587 miles ) it is much larger than any other object in this region of the solar system . It is massive enough for its gravity to have pulled it into a roughly spherical shape , which led to it being reclassified once more in 2006 , this time as a ‘ dwarf planet ’. Finally , Earth- or near-Earth-based observations of Ceres hinted at the presence of ice and clay minerals at or near its surface , and even traces of water-vapour in its proximity , indicators perhaps of a different origin to that of many asteroids and of possible geological activity at its surface .
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