Science megablast: Comets may have brought xenon to Earth

Noble gas found on 67P by Euro probe Rosetta

Scientists working on the European Space Agency’s Rosetta probe mission have found xenon on Comet 67P – a discovery that introduces a link between the cosmic rock and Earth for the first time.

The Rosetta spacecraft was launched in 2004, and its companion lander unit, Philae, arrived at the comet a decade later. Both were tasked with finding signs of how comets could uncover the origins of the solar system and life on Earth.

The latest findings have found a connection that might answer the question of how material may have been delivered to our planet, when Earth was beginning to take shape about 4.6 billion years ago.

It’s all to do with xenon; a colourless, odourless noble gas that makes up less than a billionth of the volume of Earth’s atmosphere.

Seven different isotopes of xenon and traces of krypton were identified by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. The spacecraft had to fly very close - about 5 km to 9 km from the surface of the comet’s nucleus - to pick up the xenon signatures, which are spread thinly.

The unique blend of the gas might match the concentrations found in the Earth’s early atmosphere, according to the results published in Science.

Strong and stable

"Xenon is the heaviest stable noble gas and perhaps the most important because of its many isotopes that originate in different stellar processes: Each one provides an additional piece of information about our cosmic origins," said Bernard Marty, lead author of the study and a researcher at the Université de Lorraine, France.

It can be formed in different ways such as the swelling of low- and intermediate-mass stars and supernova explosions, which lead to nuclear fusion reactions. Each method leads to a different isotope of xenon, allowing researchers to work out where the samples come from.

One of the hypotheses is that the xenon in the solar system comes from the protosolar cloud, a ball of gas and dust out of which the Sun and the planets were formed. The xenon on Earth, however, is thought to have been delivered at a later stage by comets.

The relative abundances of the various isotopes vary in the atmospheres of Earth and Mars, in meteorites, and the solar wind. It is believed that Earth once contained a higher abundance of lighter xenon isotopes, a primordial mixture known as U-xenon. But present concentrations have heavier isotopes, as the lighter ones have escaped Earth’s gravitational pull and floated off into space.

Bernard has called the discovery a potential candidate for U-xenon, which would indicate that the noble gas was indeed delivered by impacting asteroids and comets like Comet 67P.

It is estimated that comets may have brought up to 22 per cent of the xenon once present in Earth’s atmosphere.

The results also support the idea that comets could also have been carriers of pre-biotic molecules such as phosphorus and glycine, an amino acid, necessary components for life on Earth. ®

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