New evidence supports the theory that comets delivered a significant portion of Earth’s oceans, which scientists believe formed about 8 million years after the planet itself. The findings, which involve a University of Michigan astronomer, are published Oct. 5 online in Nature.
“Life would not exist on Earth without liquid water, and so the questions of how and when the oceans got here is a fundamental one,” said U-M astronomy professor Ted Bergin, “It’s a big puzzle and these new findings are an important piece.”
Bergin is a co-investigator on HiFi, the Heterodyne Instrument for the Infrared on the Herschel Space Observatory. With measurements from HiFi, the researchers found that the ice on a comet called Hartley 2 has the samechemical composition as our oceans. Both have similar D/H ratios. The D/H ratio is the proportion of deuterium, or heavy hydrogen, in the water. A deuterium atom is a hydrogen with an extra neutron in its nucleus.
This was the first time ocean-like water was detected in a comet. “We were all surprised,” Bergin said.