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Data from the comet 67P/Churyumov–Gerasimenko suggest that some of the xenon in Earth's atmosphere may have originated from comets. ESA/Rosetta/NAVCAM (CC BY-SA IGO 3.0)

Asteroids, comets and Kuiper belt

Xenon came from comets

Comets may have delivered more than one-fifth of Earth’s atmospheric xenon.

The planet’s mixture of xenon isotopes is unique within the Solar System, and the origins of a proportion of the heavy noble gas have long been a mystery. Bernard Marty at the University of Lorraine in Vandœuvre-lès-Nancy, France, and his colleagues analysed the xenon emanating from comet 67P/Churyumov–Gerasimenko, which was measured by the ROSINA spectrometer aboard the European Space Agency’s Rosetta spacecraft. 

Data from close flybys of the comet in May 2016 revealed a xenon isotopic signature that, when combined with xenon signatures from other known sources within the early Solar System, can account for Earth’s xenon mix. Comets that struck the planet early in its history probably brought enough of the element to account for 22% of its total today, say the authors.