The first results from a mission to catch dust from a comet's tail have revealed a surprise: these balls of dirty snow are born of fire as well as ice. Scientists were stunned to find a huge range of minerals in the particles captured by NASA's Stardust probe as it swooped past the cornet Wild 2 on 2 January 2004. Many of the compounds could only have formed close to a star — far from the chilly outskirts of the Solar System where the cornet first coalesced.
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