Rosetta Findings Challenge Theories of Origin of Earth’s Water
The European Space Agency (ESA’s) Rosetta spacecraft is still chasing Comet 67P/Churyumov–Gerasimenko, and its recent findings may blow away theories about how water arrived on Earth. One theory about how Earth’s oceans formed assumes that the Earth was so hot when it originally formed 4.6 billion years ago that its original water boiled off. New water had to be delivered from somewhere, most likely either comets or asteroids. Rosetta’s findings tilt the balance in favor of asteroids. The spacecraft discovered the water vapor from the comet has a chemical “flavor” that’s very different from water vapor on Earth. The “flavor” of water in this case refers to the proportion of deuterium – a form of hydrogen with an additional neutron – to normal hydrogen. The flavor should theoretically be different depending on where the water was in relation to the sun in the early solar system. Determining where is not a straightforward process, of course, as comets can get pushed out of their original orbits by the gravitational pull of