[meteorite-list] Science Journal: Earth's water didn't come from comets, scientists now say

From: Kelly Beatty <jkellybeatty_at_meteoritecentral.com>
Date: Sat, 13 Dec 2014 20:46:08 -0500
Message-ID: <E0EE02BFE38341E5A77607573A05E2E3_at_NightSkyGuy>

hi, Michael...

> I am curious how such a definitive conclusion can be reached from the
> analysis of a singular cometary body?

several others have chimed in, but let me try to add something new: it's not
just this one object, really. to date we have D:H ratios for about a dozen
comets, including one (Halley) measured in situ.

prior to this result, *all* of the comets derived from the Oort Cloud had D:H
ratios that are much too high to be compatible with Earth - and yet the two
Jupiter-Family Comets that had been measured (by ESA's Herschel space
telescope) showed D:H ratios *very* close to Earth's. there was hope.

but 67P is also a JFC, and its D:H ratio is the highest yet measured.
statistically, based on that alone, it's very unlikely that only JFCs with the
terrestrial D:H ratio would have struck Earth. it also implied that the Kuiper
Belt (source of the JFCs) must comprise objects from a mix of sources.

a plot of all the D:H ratios determined to date is in the Science paper, and
that plot appears in Sky & Telescope's write-up of this result:
http://www.skyandtelescope.com/astronomy-news/rosetta-earths-water-not-from-com
ets-120920141/


clear skies,
Kelly

****************
J. Kelly Beatty
Senior Contributing Editor
SKY & TELESCOPE
617-416-9991
SkyandTelescope.com
Received on Sat 13 Dec 2014 08:46:08 PM PST