Measurements from Rosetta’s Rosina instrument found that water on comet 67P /Churyumov-Gerasimenko contains about three times…

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Measurements from Rosetta’s Rosina instrument found that water on comet 67P /Churyumov-Gerasimenko contains about three times more deuterium – a heavy form of hydrogen – than water on Earth.

The discovery seems to overturn the theory that Earth got its water, and so its ability to harbour life, from water-bearing comets that slammed into the planet during its early history.

Comet 67P is thought to have come from what is called the Kuiper belt, a broad band of frozen bodies that begins beyond the orbit of Neptune. The main asteroid belt contains more rocky objects that circle the sun between the orbits of Mars and Jupiter.

Kathrin Altwegg at the University of Bern said that rather than comets ferrying water to Earth, it may have arrived onboard asteroids instead. Details of the discovery are reported in the journal, Science.

“Today asteroids have very limited water, that’s clear. But that was probably not always the case, said Altwegg. In the earliest period of the solar system, 3.8bn years ago, asteroids are thought to have crashed into Earth regularly in what is called the late heavy bombardment. “At that time, asteroids could well have had much more water than they have today,” Altwegg said.

The Rosina instrument measured water coming off the comet as it flew around the body. Scientists plan to take more measurements as the comet nears the sun and its begins to spew more water vapour and dust out into space.

Measurements from other comets have found water with similar deuterium contents to that on Earth. But the strange composition of comet 67P’s water suggests that the picture of comets bringing water to Earth is too simplistic.

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TIRED: comets are the source of water for Earth.

WIRED: asteroids are the life giving, death dealing forces of nature.

and my updated guide to Panspermia needs revising again.