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if all goes as planned three two we have

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main engine start in 2007 and liftoff a

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delta 2 rocket will carried on beyond

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when that dawn spacecraft lifts off and

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we're on our way to finding out about

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some of the biggest mysteries in the

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solar system that's something we can all

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be part of it's so cool going to the

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asteroid belt this ring of broken up

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debris between Mars and Jupiter these

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are among the last unexplored worlds in

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the inner solar system the asteroid belt

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is really fascinating because it's kind

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of like the boneyard of material that's

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left over from forming all these planets

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it's fragments of explosions of

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planetary embryos perhaps during

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collisions or material that's come in

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from other parts of the solar system and

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been captured into this orbit of the

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asteroid belt we're going out to Ceres

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and also to Vesta and these are very

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different bodies Vesta is the brightest

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asteroid in the solar system and the

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only one visible to the naked eye in one

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sense it's sort of like our moon but in

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another sense that's sort of like the

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earth it's got a iron core just like the

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earth does and it may have had many of

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the processes acting that the earth has

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the three science instruments on Don all

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work together to tell us about the

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surfaces of the body and from that week

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we try to work back to you know how the

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whole thing was put together and what

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happened to it scientists believe series

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represents a transition from the rocky

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terrestrial planets of the inner solar

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system through the dashes and icy worlds

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of the outer solar system

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Ceres likely has a rocky core and a very

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thick ice mantle there's even the

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possibility that there's liquid water

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under the surface of Ceres we estimated

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from our measurements with Hubble Space

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Telescope that it's got almost a hundred

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kilometres of water on top of a rocky

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core to accomplish Dawn's journey into

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the heart of the asteroid belt the

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spaceship one whose engine will work

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without fail for years at a time is

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required

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Dawn's remarkable ion engines employ

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electrical currents magnetic fields and

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xenon the high-tech innards of an ion

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engine changes xenon into a positively

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charged plasma and accelerated out the

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engine at speeds over 78,000 miles per

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hour the ion engine pushes on the

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spacecraft about as hard as the single

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piece of paper pushes on my hand but

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this very gentle thrust eventually

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builds up and allows the spacecraft to

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achieve very very high speed with the

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ion propulsion system Don will be the

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first spacecraft ever to orbit to target

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bodies after leaving Earth a mission

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into our distant past a mission for the