| Jean-Louis Santini |
WASHINGTON (AFP) – Water on Earth is more likely to have come from asteroids that hit our planet billions of years ago than comets, European researchers said on Wednesday.
Mankind’s first-ever probe of a comet came last month when the European Space Agency’s Philae lander touched down on the duck-shaped 67P/Churyumov-Gerasimenko comet, but the latest report in the journal Science comes from an instrument aboard the Rosetta spacecraft that has been studying the comet’s interior since August.
“We have to conclude… the terrestrial water was brought by asteroids more likely than comets,” said Kathrin Altwegg, principal investigator on the ROSINA mass spectrometer that has been examining the chemical fingerprint of water and other gases in the comet.
The report in the peer-reviewed US journal is based on the atomic signature of water molecules from the comet, showing that they are vastly different from water on Earth.
Scientists measure the ratio between deuterium, a hydrogen isotope, and hydrogen, which forms water when combined with oxygen.
The comet has shown “probably the highest level of deuterium to hydrogen ratio, the most heavy of any of the solar system’s bodies,” said Altwegg, a professor at the University of Bern in Switzerland.
The ratio is between 30 and 120 per cent higher than that formed in water molecules found in Halley’s comet, which belongs to the same comet family, Jupiter, formed in the Kuiper Belt.
Such a high ratio of deuterium to hydrogen “probably means that it was formed at very low temperatures and that it could be… most probably the original material from the very, very early time of our solar system, so it’s a real treasure chest to explore how our solar system looks like 4.6 billion years ago,” she said.