"The Mystery of Origin of Earth's Water Deepens" --The Rosetta Comet Mission

By: Wendy on 13:07

Results from the Rosetta mission, which made history by landing on comet 67P in November, an unprecedented, close-up look at a comet is helping scientists to answer the fundamental question of whether a bombardment of these primitive bodies brought water to Earth billions of years ago. The wealth of scientific data the touchdown gathered, shows the water on the icy mass is unlike that on our planet, that there was far more heavy water on Comet 67P than on Earth, dealing a serious blow to the theory that most water on Earth came from comets.

Earth's water on has a distinctive bio-signature. While the vast majority of our water is made up of hydrogen and oxygen atoms, a hydrogen atom will occassionaly be replaced with a deuterium atom --for every 10,000 water molecules, three deuterium atoms can be found. This water has the same physical properties as H2O, but it is heavier in mass.

The team found that there was far more heavy water on Comet 67P than on Earth: "This ratio between heavy and light water is very characteristic," Kathrin Altwegg, from the University of Bern, who is Rosina's principal investigator, told BBC News. "You cannot easily change it and it stays for a long time. If we compare the water in comets with the water we have on Earth, we can definitely say if the water on Earth is compatible with the water on comets."

Altwegg told BBC Radio 4's Inside Science programme: "It is the highest-ever measured ratio of heavy water relative to light water in the Solar System. It is more than three times higher than on the Earth, which means that this kind of comet could not have brought water to the Earth."

ESA scientists published their coclusions in the journal Science, stating that it is more likely that the water came from asteroids, but other scientists say more data is needed before comets can be ruled out.

The Rosetta probe has been orbiting Comet 67P/Churyumov-Gerasimenko since August, and on 12 November the although the Philae robot's batteries ran out soon after touchdown on 12 November its lander it gathered a goldmine of data, and the Rosetta "mothership" continues to analyse the wandering "ice mountain".