Comet challenges theories on solar system

 30 October, 2015 00:14

Explanation of the discovery of molecular oxygen in the atmosphere of comet 67P/Chury. 135 x 105 mm.
Image by: AFP

Stunned scientists have announced the unexpected discovery of large quantities of oxygen on a comet that streaked past the Sun in August, with a European spacecraft in tow.

The find came as a "big surprise", and challenges mainstream theories about the formation of our solar system, said scientist André Bieler of the University of Michigan.

Measurements made by the Rosetta probe suggested that oxygen molecules in the 67P comet's gassy halo must have existed |"before or at" its formation.

This may have implications for mankind's understanding of the chemistry involved in the formation of the universe about 4.6billion years ago.

"We believe this oxygen is primordial, which means it is older than our solar system," said Bieler.

As oxygen mixes easily with other elements, "we never thought that oxygen could survive for billions of years" in a pristine state, said Kathrin Altwegg of the University of Bern, who co-authored a study in the journal Nature.

"This evidence of oxygen will likely discredit some theoretical models of the formation of our solar system," she said.

The comet is being tracked on its deep space journey around the Sun by the European Space Agency's Rosetta spacecraft. The historic mission seeks to unlock the mystery of the origins of life on Earth.

Scientists believe that comets "seeded" early Earth with some of the ingredients for life.

The team monitored the ratio of oxygen to water on the comet to see if the gas molecules would dissipate as solar winds ripped away layers of surface. They did not, proving oxygen was embedded, not just hanging around its surface.

Prevailing theories of the solar system's birth posit a chaotic, collision-strewn mixing of matter flowing towards and away from the newly formed Sun. Pristine, icy grains containing oxygen would not have made it through such violence intact, the scientists said, leading them to speculate that the process was, in fact, "gentler".

The oxygen molecules must have "survived from the dark molecular clouds from which they were probably formed into comets as we have them today", said Altwegg.

Only twice before - on the icy moons of Jupiter and Saturn - have oxygen molecules been found beyond Earth's atmosphere, and never before on a comet.

Oxygen is difficult to detect with Earth-bound telescopes. Rosetta offered a rare opportunity to study 67P's "coma" - the envelope of dust, gas and ice that forms as it nears the Sun on an elliptical orbit.

Scientists not involved in this study underlined its importance, but said more time was needed to assess the implications.

The discovery "imposes a severe constraint on the mechanism for the formation of the solar system", said French astrophysicist Francis Rocard. "But we shouldn't jump to conclusions," he cautioned.

Oxygen molecules were the fourth-most common gas detected in 67P's halo - after hydrogen, carbon monoxide and carbon dioxide. But their presence did not tell us anything about the origins of life on Earth, or of the possibility of finding it elsewhere, Altwegg said.

In looking at exoplanets, "the combination of oxygen and methane has been taken as a sign that you might have life underneath", she said.

"On this comet we have both, but we don't have life. So having oxygen may not be a very good biosignature.
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