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Where Earth got its water

Sun, 9th Oct 2011

Chris Smith

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A comet not far from Earth has shed some light on how our planet could have Comet 103P/Hartley 2come by much of its water, a new study has revealed.

Writing in Nature, Paul Hartogh, who is based at Germany's Max Planck Institute for Solar System Research, used ESA's orbiting Hershel Space Observatory to study a small 1.5 kilometre-wide comet called 103P/Hartley 2, which formed originally out in the Kuiper Belt beyond the orbit of Pluto and now follows a 6.5 year elliptical orbit in the region of space between the Earth and Jupiter.

Hartogh and his colleagues probed the comet's "coma" - the pall of dust and debris thrown off by the body as it is warmed by the Sun - for the telltale-traces of water.  Specifically, they were looking at the relative proportions of "heavy" hydrogen - or deuterium - that were present.

Water on Earth contains about one atom of deuterium for every 6500 atoms of "light" hydrogen. This a close match for the levels seen in asteroids and many meteorites but about half as large as the levels seen in other comets that have been measured far out in deep space in a region called the Oort cloud.

Consequently, space scientists had concluded that when the Earth first formed it was a hot, dry and barren rock that, as it cooled sufficiently for liquids to condense, was progressively wetted by the arrival of water-laden asteroids. Comets, they thought, must have been a relatively rare contributor to the planet's early water supply.

However, the observations from 103P/Hartley turn this idea on its head. The comet shows a deuterium-hydrogen fingerprint that is almost exactly the same as Earth's own water. It also reveals some interesting details about the birthplaces of the comets themselves and therefore the structure of the early solar system.

Comets like 103P/Hartley are thought to have formed in the Kuiper Belt, about 50 times further from the Sun than Earth is, and then migrated inwards later. Conversely, more distant comets like those now in the Oort Cloud and over 5000 times the Earth-Sun distance away, are thought originally to have been born near Jupiter before being gravitationally booted into the outer reaches of the solar system later.

But because these Oort Cloud comets formed closer to the Sun originally, and therefore would have been exposed to higher temperatures, they should have a lower deuterium-hydrogen ratio than their Kuiper Belt counterparts that formed under cooler conditions.

Instead the scientists have found the opposite. This argues that something is out of kilter in our understanding of the formation of the early Solar system, but it will take further cometary chemical forensics, like that announced by Hartogh, to ultimately reveal the answer...

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     I do appreciate the 'new' scientific information concerning how potentially the earth has received its vast resource of oceans and fresh water for that matter in which covers 3/4's of the earth.  I find it humorous in a way mainly because of the size of the comet or asteroid involved in bringing our water supply to us.  The question still remains, where did that comet or asteroid gain the water from in order to ingratiate our good earth?  Here is a fact:  The universe is comprised of Hydrogen and oxygen and, so many other elements that comprise earth and all of our other planets throughout our universe.  It all depends on how far they are away from a sun.  Good luck with your idea though.  It might have some possibilities if the asteroid somehow compacted all of the water it had and somehow opened up like a compacted zip file or something.  Sorry.  I could not resist.  Am I wrong?  Maybe I didn't get what you were saying.  Could be.  I am always open for argument.  I love to equate based on what I read and see..  Help me out if I am missing something.  Thanks..        swadewade8, Fri, 18th Nov 2011

I think the only thing you are missing is an understanding of the research.

You seem to be aware that during formation of the terrestrial planets volatiles were relatively depleted, so although water is a commonplace compound in the universe it was deficient in the formation of the Earth. (You noted: The universe is comprised of Hydrogen and oxygen and, so many other elements that comprise earth and all of our other planets throughout our universe.  It all depends on how far they are away from a sun.) This depletion seems to rule out the notion that the oceanic water was produced largely by degassing of the Earth's interior.

The alternative explanation was that the water had been acquired through impact by many bolides (comets or asteroids) from the formation of the Earth through the Late Heavy Bombardment period. Please note that a single comet or asteroid is not seen as the source of the water, but rather very many such bodies. (A really big number. Work it out - simple arithmetic.)

You ask where the comet or asteroid would have acquired this water. They would have formed sufficiently distant from the proto sun that water could condense, along with dusty material, and accrete into small bodies, either asteroids (with hydrous minerals) or comets (which are still reasonably called 'dirty snowballs').

Arguments as to whether the bulk of the water came from asteroids or comets have swayed back and forth. This latest research points in the direction of comets. Ophiolite, Fri, 18th Nov 2011


You seem to be aware that during formation of the terrestrial planets volatiles were relatively depleted, so although water is a commonplace compound in the universe it was deficient in the formation of the Earth. (You noted: The universe is comprised of Hydrogen and oxygen and, so many other elements that comprise earth and all of our other planets throughout our universe.  It all depends on how far they are away from a sun.) This depletion seems to rule out the notion that the oceanic water was produced largely by degassing of the Earth's interior.. 

I appreciate your comment(s) in its entirety.  I would like to further elaborate on why I made some of the comments I did.  The entire universe contains essentially all of the same elements or molecular structure(s) throughout.  These can vary by either gravitational force or even perhaps vary because of the distance from a (the) sun.  For instance, the terrestrial planets are different from the Jovian Planets in that they vary in degree because of distance and gravity.  One will find that generally the 'larger' planet(s) will be farther away from the sun because the distance generally will not allow the planet to warm up or burn off certain elements (depending how far away the planet is away from the sun of course) the mass tends to in time grow due to gravitational forces creating more mass overall (without the threat of 'burning off' as other planets do that are closer to the sun.  Earth is in an amazing position that allows life mainly because of size of the sun in comparison to the distance to our planet.  They are in 'Harmony'.  As far as water goes, yes, you are right about the icy comets beyond our solar system that do make they way towards us, but at the same time I believe our water supply overall has to do with the Earth's complementary position to the sun and the Earth's orbit around the sun in which is a unique combination that allows life to exist as it would anywhere else in our universe given the same circumstances.  :)  Thank you for your input!  swadewade8, Tue, 22nd Nov 2011




http://news.nationalgeographic.com/news/2011/06/110613-space-science-star-water-bullets-kristensen/

. Silver, Tue, 22nd Nov 2011

New Big Bang theory from Terridactyl split off to New Theories

http://www.thenakedscientists.com/forum/index.php?topic=42202.msg373613#msg373613

Thanks

imatfaal - moderator imatfaal, Wed, 23rd Nov 2011

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