archiv~1.txt: SETI [ASTRO] Earth's Water Probably Didn't Come From Comets,

SETI [ASTRO] Earth's Water Probably Didn't Come From Comets,

Larry Klaes ( lklaes@bbn.com )
Fri, 26 Mar 1999 12:37:28 -0500

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>Date: Fri, 26 Mar 1999 15:35:07 GMT
>From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>To: astro@lists.mindspring.com
>Subject: [ASTRO] Earth's Water Probably Didn't Come From Comets, Caltech
Researchers Say
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>Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>
>
>Caltech Media Relations
>
>Contact: Robert Tindol
> (626) 395-3631
> tindol@caltech.edu
>
>Earth's water probably didn't come from comets, Caltech researchers say
>
>PASADENA -- A new Caltech study of comet Hale-Bopp suggests that comets did
>not give Earth its water, buttressing other recent studies but 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.
>
>"An important question has been whether comets provided most of the water
>in Earth's oceans," says 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?"
>
>The answer lies in the Blake team's measurement of a form of heavy water
>called HDO, which can be measured both in Earth's oceans using mass
>spectrometers and in comets with Caltech's Owens Valley Radio Observatory
>(OVRO) Millimeter Array. Just as radio waves go through clouds,
>millimeter waves easily penetrate the coma of a comet.
>
>This is where cosmochemists can get a view of the makings of the comet
>billions of years ago, before the sun had even coalesced from an
>interstellar cloud. In fact, the millimeter-wave study of deuterium in
>water and in organic molecules in the jets emitted from the surface of
>the nucleus shows that Hale-Bopp is composed of 15 to 40 percent
>primordial material that existed before the sun formed.
>
>The jets are quite small in extent, so the image clarity provided by the
>OVRO Millimeter Array was crucial in the current study. "Hale-Bopp came
>along at just the right time for our work," Blake says. "We didn't have
>all six telescopes in the array when Halley's comet passed by, and
>Hyakutake was a very small comet. 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 that 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.
>
>Also involved in the Nature study are Charlie Qi, a graduate student in
>planetary science at Caltech; Michiel Hogerheijde of the UC Berkeley
>department of astronomy; Mark Gurwell of the Harvard-Smithsonian Center
>for Astrophysics, and Duane Muhleman, professor emeritus of planetary
>science at Caltech.
>
>For full diagrams and further illustration of Geoff Blake's recent study
>see the Planetary Science's Press Release,
>
> http://www.gps.caltech.edu/~pa/press.html
>
>Related Links
>
>The Division of Geological and Planetary Sciences at Caltech
>http://www.gps.caltech.edu/
>
>Nature
>http://www.nature.com/
>
>