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Researchers: Earth's water probably didn't come from comets

Comet Hale-Bopp
Comet Hale-Bopp   

March 30, 1999
Web posted at: 2:18 p.m. EST (1918 GMT)

PASADENA, California (CNN) -- A new Caltech study of comet Hale-Bopp suggests that comets did not give Earth its water, contrary to the longstanding belief of many planetary scientists.

In the March 18 issue of Nature, cosmochemist Geoff Blake and his team show that Hale-Bopp contains sizable amounts of "heavy water," which contains a heavier isotope of hydrogen called deuterium.

Thus, if Hale-Bopp is a typical comet, and if comets indeed gave Earth its water supply billions of years ago, then the oceans should have roughly the same amount of deuterium as comets. In fact, the oceans have significantly less, the researchers said.

"An important question has been whether comets provided most of the water in Earth's oceans," said Blake, professor of cosmochemistry and planetary science at Caltech. "From the lunar cratering record, we know that, shortly after they were made, both the moon and Earth were bombarded by large numbers of asteroids or comets.

"Did one or the other dominate?"

Blake's team used Caltech's Owens Valley Radio Observatory (OVRO) Millimeter Array to study organic molecules in the jets emitted from the surface of Hale-Bopp's nucleus. The results show that Hale-Bopp is composed of 15 to 40 percent primordial material that existed before the sun formed.

"Hale-Bopp came along at just the right time for our work," Blake said. "Hale-Bopp was quite large, and so it was the first comet that could be imaged at high spatial and spectral resolution at millimeter wavelengths."

One other question the current study indirectly addresses is the possibility that comets supplied Earth with the organic materials that contributed to the origin of life. While the study does not resolve the issue, neither does it eliminate the possibility, the researchers said.

Comet Hale-Bopp

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Comet Hale-Bopp: Snapshots

Planetary Science's press release
The Division of Geological and Planetary Sciences at Caltech
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