For more than two years a spacecraft called Genesis loitered in a holding pattern a million miles sunward of Earth. Its job: Pick up particles of the sun cast out by the exhalation known as the solar wind. According to planetary scientists, a sample of the solar wind far away from the Earth's magnetosphere will reveal the precise abundances of isotopic oxygen, nitrogen, helium, neon, and other constituents of the nebula that collapsed 4.6 billion years ago to form the sun and planets. Determining the precise mixture of ingredients can help explain how the solar system formed and why the compositions of its bodies differ so significantly.
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