A Comet Dates Jupiter

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Science  03 Feb 2012:
Vol. 335, Issue 6068, pp. 504
DOI: 10.1126/science.335.6068.504-a

In 2004, NASA's Stardust mission flew by comet Wild 2 and retrieved particles from the comet's coma, the tail of dust and gas that forms when a comet approaches the Sun. Two years later, those particles were brought to Earth and analyzed by international teams of scientists. Ogliore et al. describe mineralogical and isotope data for a fragment from the Stardust collection. This fragment, named Iris, resembles chondrules, the type of round, once-molten silicate particles typically found in meteorites. Iris probably formed in the inner solar nebula, and thus its presence in the coma of comet Wild 2 is a testament to the transport of particles from the inner, hotter parts of the solar nebula to the outer, colder ones, where comets originate. Iris formed at least 3 million years after the formation of the earliest solids in the solar system. Transport of material across the solar system must have occurred before Jupiter formed, as its growing embryo would have opened a gap in the protoplanetary disk, preventing outward transport past its orbit. Thus, unless transport occurred outside the plane of the protoplanetary disk or Jupiter was interior to Iris when this particle formed, the results imply that Jupiter formed 3 million years after the formation of the earliest solids.

Astrophys. J 745, L19 (2012).

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