Isotopes Say New Origin Stories for Some Planets

If you’ve ever wondered where the Earth came from, the answer, it seems, is blowing in the wind—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 arose from 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 ratio of oxygen and nitrogen isotopes found in the solar wind is different from the ratio 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 excess 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 carbon copy.