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Progress
Nature 424, 639-642 (7 August 2003) | doi:10.1038/nature01725
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Single-cell Analysis Platform
This Challenge is looking for novel approaches to analyzing changes at a single-cell level. This is...
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Direct Molecular Detection of Proteins and Nucleic Acids
This Challenge is looking for novel approaches to protein and nucleic acid detection. This is an Id...
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One Postdoctoral Position at Centre for Research in Agricultural Genomics
- The Centre for Research Agricultural Genomics Consorcio CSIC-IRTA-UAB
- Barcelona Spain
Oleo Chemistry
- Praj Matrix - Praj Industries Ltd
- Pune, Maharashtra Pune-411021 India
The evolution of comets in the Oort cloud and Kuiper belt
S. Alan Stern
Abstract
Comets are remnants from the time when the outer planets formed, 
4–4.5 billion years ago. They have been in storage since then in the Oort cloud and Kuiper belt—distant regions that are so cold and sparsely populated that it was long thought that comets approaching the Sun were pristine samples from the time of Solar System formation. It is now recognized, however, that a variety of subtle but important evolutionary mechanisms operate on comets during their long storage, so they can no longer be regarded as wholly pristine.
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