If you’ve ever wondered where the Earth came from, the answer, it seems, is ___1___—the solar wind. Or so say scientists who, after examining solar wind samples collected by the Genesis spacecraft, conclude that the inner planets of our solar system formed a little differently than we’d thought. The work appears in the journal Science. [Bernard Marty et al., "A 15N-Poor Isotopic Composition for the Solar System as Shown by Genesis Solar Wind Samples"]

Our solar system ___2___ a large, rotating cloud of interstellar debris called the solar nebula. The sun came first and the planets followed not long after.

But the new study shows that the ___3___ of oxygen and nitrogen isotopes found in the solar wind is different from the ___3___ here on earth, or on the moon or Mars. We’ve got more of the heavier versions of these atoms than our Sun does.

Now we just have to figure out why. Scientists say the ___4___ heavy nitrogen could have come from a comet. And the heavier oxygen from a natural process that left more of the light isotope in the part of the nebula that made the sun. So we are made of star stuff. But when it comes to our elemental composition, we’re not a ___5___.
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