Posted by Will Sullivan on Thu, 15 Jun 2017

Comets hurtling through space 3.54.5 billion years ago may have deposited heavy isotopes of xenon into Earths atmosphere. This clue to the isotopes mysterious origins suggests that comets visited Earth in its earliest days, that the moon and atmosphere are younger than we originally thought, and that comets might have delivered the first organic material to our fledgeling planet.

While there are only trace amounts of xenon in the atmosphere, the noble gas doesnt chemically react with other elements, meaning its a relatively stable marker whose origin is easy to trace.

Comet 67P/Churyumov-Gerasimenko

But the presence of a surprisingly high percentage of heavy xenon isotopes in Earths atmosphere has hampered our understanding of our planets origins. Scientists previously couldnt find any plausible sources for these heavier isotopessolar wind and meteors, for example, only contain lighter isotopes.

The new data comes from gas collected during the Rosetta mission, which flew a spacecraft near the surfaceof 67P/Churyumov-Gerasimenko, a member of the family of comets controlled by Jupiters gravity. The samples contained a mixture of three noble gases, krypton, argon, and xenon. This comets xenon contained the same perplexing heavy isotopes, suggesting that Earth may have received a fraction of its xenon from comets. The model that best fits the atmospheres xenon makeup estimates that about 22% of it came from comets.

These new findings allow scientist to correct small errors in dating the planets evolution. Heres Leah Crane for New Scientist:

On Earth, we presumed the presence of this isotope was primarily a result of decaying iodine. We know the rate at which iodine decays, so we use the quantity of xenon-129 to gauge the time at which planetary events took place. But if 22 per cent of the xenon in Earths atmosphere was transported by comets, models based on iodine decay arent accurate. They overestimate the age of Earths atmosphere and the moon.

Since this study only examines data from one comet, missions to other comets will need to verify the results. But this cometary xenon further links Earths birth with the rest of the solar system. Results from other comets will provide further details of Earths formative years and perhaps even an explanation for how the first organic molecules arrived on Earth.

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Ancient Comets May Have Delivered Xenon To Earth - NOVA Next