Stardust & Comets
Red/green stereo anaglyph of Comet Wild 2 Credit: NASA JPL Stardust
Stardust reveals turbulent start to the Solar System
Analysis of comet samples brought back to earth by NASA's Stardust mission reveal that the start of the Solar System was a lot more turbulent than first thought. Dust particles from comet Wild 2 are found to originate from both the inner reaches and outer edges of the Solar System indicating a massive amount of mixing of particles prior to the formation of the comet. The findings of the initial analysis of comet samples were published in Science (15th Dec 2006).
The precious cometary samples were collected by the Stardust spacecraft which journeyed 2.88 million miles during a seven year round trip from Earth to comet Wild 2 and back again. Following the capture of the particles from the comet in January 2004 the capsule containing the interstellar cargo was returned to Earth in January 2006. After its retrieval from the Utah desert grains of the comet were distributed to worldwide teams of scientists to begin the initial analysis.
Many of the grains were silicates - iron and magnesium rich grains that are the usual constituents commonly observed around newly forming stars where planets are being created. But one of the most exciting results was that some of the dust grains were not silicates, but were rich in calcium and aluminium, grains that are only produced at very high temperatures. This is important because it shows that some of the dust must have been formed very close to the centre of our Solar System. And it leaves a mystery as to how they managed to become mixed in with the rest of the dust and gas that made up the comets, forming on the outer edges of the Solar System.
We have not yet begun to unravel the relationship between the organic and inorganic parts of the comet dust.
Using spectroscopy technology, which does not damage the mineral content of the particles, the Stardust scientists from Imperial College London and the Natural History Museum have found that the comet dust is made up of many different mineral compositions rather than a single dominant one. This implies that the dust was formed in many different environments before coming together to make the comet, indicating a great deal of mixing in the early Solar System prior to the formation of the planets.
Of particular significance is the discovery of calcium aluminium inclusions, which are amongst the oldest solids in the Solar System and are thought to have formed close to the young Sun. This discovery suggests that the components of the comet came from all over the Solar System, with some dust having being formed close to the Sun and other material coming from the asteroid belt between Mars and Jupiter.
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