[meteorite-list] Did Comets Flood Earth's Oceans?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jun 17 16:06:19 2004
Message-ID: <200406172005.NAA10811_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaCP/SEMGX93VQUD_index_0.html
 
Did comets flood Earth's oceans?
European Space Agency
16 June 2004
 
Did the Earth form with water locked into its rocks, which then
gradually leaked out over millions of years? Or did the occasional
impacting comet provide Earth's oceans? The Ptolemy experiment on
Rosetta may just find out...
 
The Earth needed a supply of water for its oceans, and the comets are
large celestial icebergs - frozen reservoirs of water orbiting the Sun.

Did the impact of a number of comets, thousands of millions of years
ago, provide the Earth with its supply of water? Finding hard scientific
evidence is surprisingly difficult.
 
Ptolemy may just provide the information to understand the source of
water on Earth. It is a miniature laboratory designed to analyse the
precise types of atoms that make up familiar molecules like water.

Atoms can come in slightly different types, known as isotopes. Each
isotope behaves almost identically in a chemical sense but has a
slightly different weight because of extra neutrons in its nucleii.

Ian Wright is the principal investigator for Ptolemy, an instrument on
Rosetta's Philae lander. By analysing with Ptolemy the mix of isotopes
found in Comet 67P/Churyumov-Gerasimenko, he hopes to say whether comet
water is similar to that found in Earth's oceans. Recent results from
the ground-based observation of another comet, called LINEAR, suggested
that they probably are the same.

If this is true, then scientists have solved another puzzle. However, if
the comets are not responsible for Earth's oceans, then planetary
scientists and geophysicists will have to look elsewhere.

For example, the answer could be closer to home, through processes
related to vulcanism. Also, meteorites (chunks of asteroids or comets
that fall to Earth) have been found to contain water but it is bound to
the minerals and in nothing like the quantity found in comets.

However, since the Earth formed from rocks similar to the asteroids, it
is feasible that enough water could have been supplied that way.

If comets did not supply Earth's oceans then it implies something
amazing about the comets themselves. If Ptolemy finds that they are made
of extremely different isotopes, it means that they may not have formed
in our Solar System at all. Instead, they could be interstellar rovers
captured by the Sun's gravity.

Rosetta, Philae and Ptolemy will either solve one scientific mystery, or
open another whole set of new ones.
Received on Thu 17 Jun 2004 04:05:40 PM PDT