Solar system ice: Source of Earth's water

Jul 12, 2012
meteorite

Scientists have long believed that comets and, or a type of very primitive meteorite called carbonaceous chondrites were the sources of early Earth's volatile elements—which include hydrogen, nitrogen, and carbon—and possibly organic material, too. Understanding where these volatiles came from is crucial for determining the origins of both water and life on the planet. New research led by Carnegie's Conel Alexander focuses on frozen water that was distributed throughout much of the early Solar System, but probably not in the materials that aggregated to initially form Earth.

The evidence for this ice is now preserved in objects like comets and -bearing carbonaceous . The team's findings contradict prevailing theories about the relationship between these two types of bodies and suggest that meteorites, and their parent asteroids, are the most-likely sources of the Earth's water. Their work is published July 12 by Science Express.

Looking at the ratio of hydrogen to its heavy isotope deuterium in frozen water (H2O), scientists can get an idea of the relative distance from the Sun at which objects containing the water were formed. Objects that formed farther out should generally have higher deuterium content in their ice than objects that formed closer to the Sun, and objects that formed in the same regions should have similar hydrogen isotopic compositions. Therefore, by comparing the deuterium content of water in carbonaceous chondrites to the deuterium content of comets, it is possible to tell if they formed in similar reaches of the .

It has been suggested that both comets and carbonaceous chondrites formed beyond the orbit of Jupiter, perhaps even at the edges of our Solar System, and then moved inward, eventually bringing their bounty of volatiles and organic material to Earth. If this were true, then the ice found in comets and the remnants of ice preserved in carbonaceous chondrites in the form of hydrated silicates, such as clays, would have similar isotopic compositions.

Alexander's team included Carnegie's Larry Nitler, Marilyn Fogel, and Roxane Bowden, as well as Kieren Howard from the Natural History Museum in London and Kingsborough Community College of the City University of New York and Christopher Herd of the University of Alberta. They analyzed samples from 85 carbonaceous chondrites, and were able to show that carbonaceous chondrites likely did not form in the same regions of the Solar System as comets because they have much lower deuterium content. If so, this result directly contradicts the two most-prominent models for how the Solar System developed its current architecture.

The team suggests that formed instead in the asteroid belt that exists between the orbits of Mars and Jupiter. What's more, they propose that most of the on Earth arrived from a variety of chondrites, not from comets.

"Our results provide important new constraints for the origin of volatiles in the inner Solar System, including the Earth," Alexander said. "And they have important implications for the current models of the formation and orbital evolution of the planets and smaller objects in our Solar System."

Explore further: Cassini sees sunny seas on Titan

More information: "The Provenances of Asteroids, and Their Contributions to the Volatile Inventories of the Terrestrial Planets," by C.M.O’D. Alexander et al , Science, 2012.

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GSwift7
4.2 / 5 (5) Jul 12, 2012
It will be interesting to see how other experts respond to this. It is not uncommon to see letters published several months later in response to studies like this one. Science express is very casual about peer review. Not all of the articles are peer reviewed. The authors here will probably publish a more extensive article in one of the peer reviewed journals later, after they get feedback from the community. Since this study contradicts so much previous work, I wouldn't be surprised if there are questions and suggestions from other experts.
Vendicar_Decarian
2.5 / 5 (11) Jul 13, 2012
Impossible!

God is the source of Earth's water.
kevinrtrs
1.6 / 5 (19) Jul 13, 2012
and then moved inward, eventually bringing their bounty of volatiles and organic material to Earth.

A difficulty with this idea is that it raises the issue of why only earth has such a lot of water? Why not Venus or Mars, especially Mars. After all these other two planets are in the vicinity of earth. The scenario[or story] as it stands now, proposes that water came to earth on an extremely special course that cuts out Venus and Mars which really makes nonsense of it occurring at all.
One cannot claim that there once was water [in huge quantities] on Mars since the evidence is just not there - no matter how one interprets the geological features we can observe. Venus on the other hand clearly shows there's zero water to be found there because of it's extreme environment. The researchers have to go back to the drawing board on this and find an explanation for why those two planets are devoid of copious amounts of water.
Kedas
4 / 5 (4) Jul 13, 2012
Give me one planet or moon from which we know that there is no water and never have been.
SoylentGrin
4.3 / 5 (6) Jul 13, 2012
One cannot claim that there once was water [in huge quantities] on Mars since the evidence is just not there - no matter how one interprets the geological features we can observe.

Yeah, all those geologic features that could only form in the presence of water, all those minerals the rovers find that can only form via water, all the hematite, all the river delta features, the ice caps... Forget everything we can actually observe! Who are you going to believe: Bronze age myths or evidence, facts and your own lying eyes?
roboferret
4.2 / 5 (5) Jul 13, 2012

A difficulty with this idea is that it raises the issue of why only earth has such a lot of water?

Wrong.

Why not Venus or Mars, especially Mars. After all these other two planets are in the vicinity of earth. The scenario[or story] as it stands now, proposes that water came to earth on an extremely special course that cuts out Venus and Mars which really makes nonsense of it occurring at all.

Your lies are making nonsense. No-one is claiming that, its a ridiculous strawman.

One cannot claim that there once was water [in huge quantities] on Mars since the evidence is just not there - no matter how one interprets the geological features we can observe.

More lies. http://en.wikiped..._on_Mars READ IT.

Venus on the other hand clearly shows there's zero water to be found there because of it's extreme environment.


You sort of answered your own question there. With a surface temperature of 460C how much were you expecting?
roboferret
4.3 / 5 (6) Jul 13, 2012
In addendum, Jupiter's moon Europa ALONE has TWICE the amount of water that the Earth has. You can't get away with lies on here Kev, or are you that ignorant?
barakn
3.4 / 5 (5) Jul 13, 2012
Atmospheric sulfuric acid is the remnant of the Venusian water.
GSwift7
4.4 / 5 (7) Jul 13, 2012
or are you that ignorant?


Yes.

It's really funny. He read the article above, which has several points I would question for good reasons, but he missed all of those points. In stead, he uses the questionable article above as evidence that the majority of astronomical theory is wrong. Then he makes it even worse by demonstrating that he doesn't even know what the current theory is. lol. It's like this: "well, I don't know anything about it, but it's wrong wrong wrong!!!"
GSwift7
3.4 / 5 (5) Jul 13, 2012
Atmospheric sulfuric acid is the remnant of the Venusian water


No, the sulfuric acid there is anhydrous; it is sulfur dioxide. It's a gas, not liquid. The most abundant element in Venus' atmosphere is oxygen, but it's all locked with carbon in the form of carbon dioxide. Mainstream theory says that Venus once had oceans just like Earth, but all the hydrogen vented out to space because Venus doesn't have a magnetic field. Without a magnetic field, the radiation from the Sun can dissociate hydrogen from its bond with oxygen, which makes it so light that it escapes into space. That left the oxygen to bond with carbon in stead, and a little bit of sulfur too, though there's not really that much sulfur either.
GSwift7
5 / 5 (2) Jul 13, 2012
Here's a cool thing to try to imagine: The atmosphere on Venus is over 90 times more dense than here on Earth, and the gravity is almost identical. Here on Earth, if you throw a balloon, it only goes a short distance before wind resistance stops it. If you throw a more dense object, such as a golf ball, it will travel much farther before being slowed by friction. On Venus, the air is so much more dense that throwing a football would be like throwing a balloon here; it would only go a couple of feet, and the air would carry it around easily. With a density of about 6.5 percent the density of water, you would feel the resistance of trying to move in the Venus atmosphere. Even a small amount of wind would have enough force to blow you over, and tornado winds would carry the force of a bomb blast. The opposite would be true on Mars; a bomb blast would only have a fraction of the power it has here (the shockwave in the air, that is).
SteveL
3 / 5 (2) Jul 13, 2012
Mainstream theory says that Venus once had oceans just like Earth, but all the hydrogen vented out to space because Venus doesn't have a magnetic field. Without a magnetic field, the radiation from the Sun can dissociate hydrogen from its bond with oxygen, which makes it so light that it escapes into space.
I wouldn't be suprised if some of the hydrogen from Venus was carried outward by the solar winds and caught by Earth's greater gravity.
LagomorphZero
5 / 5 (1) Jul 13, 2012
"Objects that formed farther out should generally have higher deuterium content in their ice than objects that formed closer to the Sun, and objects that formed in the same regions should have similar hydrogen isotopic compositions."

I'm curious how they arrived at this assumption. Why would deuterium be more concentrated further from the sun?

The only idea I can think of is that the ratio of H to D would change because of the D's higher mass and be more likely to be drawn in to the sun by gravity, but it seems like the ratio would still be constant since mass is never a divisor in gravity equations. Perhaps I'm looking at the wrong equations tho.
barakn
3.7 / 5 (3) Jul 13, 2012

No, the sulfuric acid there is anhydrous; it is sulfur dioxide. It's a gas, not liquid.

Feel free to apologize for being wrong any time. Nobody calls sulfur dioxide "anhydrous sulfuric acid." Also, if the sulfur-containing compound is always a gas, then what the hell are the clouds made of? The sulfuric acid is so abundant that its presence has been known for decades. Only recently were they able to detect the tiny amount of sulfur dioxide present. And look - I am siting a source: http://phys.org/n...key.html
Torbjorn_Larsson_OM
3.7 / 5 (3) Jul 13, 2012
I found that press release somewhat curious. What I know of, comets have been considered a major water source for inner planets for some time. Earth D/H ratio precludes anything more than ~ 10 % contribution from comets IIRC.

Chondrites may have provided the dominant part of Earth water.

The continued late accretion, after the Earth core formation stopped, could have added ~ 0.3 0.8 % of mantle mass. Since the core is ~ 30 percent by mass and carbonaceous chondrites have ~ 10-20 % water by mass, the water supplied would be ~ 0.3*(0.1*0.003 0.2*0.008) or ~ 0.01 0.05 % by mass.

Earth has ~ 0.05 % by mass water, ~ 0.023 % as ocean and about as much in the crust and mantle.
Torbjorn_Larsson_OM
3.7 / 5 (3) Jul 13, 2012
But recent finds predict that Moon and Mars mantles originally had about the same water content as Earth. Naively it is difficult to predict that from impactors. For example, the Moon which originated before the late heave bombardment would have had ~ 20 times less late accretion than the gravitationally larger target Earth.

Perhaps most water was present at accretion. One mechanism would have been physisorption to dust which can retain that much water up to ~ 500 K in the disk. IIRC the disk close to the protostar would have reached ~ 1000 K as witnessed by some found grains, while the ice line of ~ 0 K lies should have formed between Mars and Jupiter I think. (Ceres is believed to have lots of ice; certainly Europa has.)
Torbjorn_Larsson_OM
3.7 / 5 (3) Jul 13, 2012
Of course a generic process for terrestrial water, if it is borne out by the new finds, is promising. Our creationist with his ludicrous puerile willful ignorance of the problem is hilarious, since the astrobiological problem is neither that Earth is as wet as most bodies are or too dry.

The problem is that Earth water can neither be about 5 times less, or we would have no plate tectonics, or about 5 times more, or we would not have continents for habitability as we know it. The marginal plate tectonics is because Earth is a runt as planets go, and needs water for enough viscous mantle. Luckily most terrestrials are superEarths, which doesn't have problem with having plate tectonics.

And if there is a generic dryness of terrestrials in the HZ, there will be many more habitable Earth analogs than we expected.
Torbjorn_Larsson_OM
3.7 / 5 (3) Jul 13, 2012
@ GSwift7:

I don't think the question of Venus water loss is settled yet. The Mars finds means initial hydrogen is mostly mantle derived. UV photolysis means hydrogen can escape while oxygen (which escapes too, see Venus Express) can oxidize minerals and especially carbon. Likely all terrestrials had initially CO2/H2 atmospheres, with some water as excess.

If there was more than 30 % hydrogen initially, you would have an hydrodynamic escape, taking some other gases with. But later atmospheric escape is different on different planets.

http://en.wikiped...c_escape : "The dominant non-thermal loss processes for Venus and Mars, two terrestrial planets without magnetic fields, are dissimilar. The dominant non-thermal loss process on Mars is pick-up from solar winds, because the atmosphere is not dense enough ... The dominant loss process for Venus is loss through electric force field acceleration." (Well, maybe.)
Torbjorn_Larsson_OM
3.7 / 5 (3) Jul 13, 2012
@ LagomorphZero: http://adsabs.har...nf..403A : "Despite the higher densities in protoplanetary disks, deuterium fractionation occurs in a similar way as in molecular clouds".

As I remember it this roughly still stands: essentially chemical reactions bumps up D/H ratio (mostly, a heavier D moves slower and is easier to catch - but they seem to insist on making simple physics a quantum mechanics model in that paper) and embeds them into grains. The farther out, the longer processed the grains are before the disk disperses by planet formation and solar irradiation, the more D/H.
jimbo92107
3 / 5 (2) Jul 15, 2012
I will further postulate that solar system rock is the source of earth's mountains.
Gaina
3 / 5 (2) Jul 15, 2012
I found that press release somewhat curious. What I know of, comets have been considered a major water source for inner planets for some time. Earth D/H ratio precludes anything more than ~ 10 % contribution from comets IIRC.

Chondrites may have provided the dominant part of Earth water.

The continued late accretion, after the Earth core formation stopped, could have added ~ 0.3 0.8 % of mantle mass. Since the core is ~ 30 percent by mass and carbonaceous chondrites have ~ 10-20 % water by mass, the water supplied would be ~ 0.3*(0.1*0.003 0.2*0.008) or ~ 0.01 0.05 % by mass.

Earth has ~ 0.05 % by mass water, ~ 0.023 % as ocean and about as much in the crust and mantle.

I knew very well that the main supplier of watter onto the Earth were comets. Since this moment we should take into account the contribution of Carbonaceous chondrites. Another new question arise: why similar processes of water accumultaion does not occur on oours nearest planets: Venus and Mars?
Gaina
3 / 5 (2) Jul 15, 2012
The answer which I know from the school is: the magnetic field on the Venus is very week or absent, while in the case of Mars: the activity of some elementary life forms (beings) damaged Its atmosphere.

The article and its discussion suggests that the problem of water on the planet Earth has a new feature: the Carbonaceous chondrites.
Gaina
3 / 5 (2) Jul 15, 2012
A very short extraction from the "Oxford Dictionary of Astronomy" (Ed. I. Radpith) about Carbonaceus chondrites: "*Carbonaceous or C-chondrites contain about 3% carbon; These have the highest proportions of volatile substances, and are the most oxidized" (p. 81, Ed. 2004)
antialias_physorg
3 / 5 (2) Jul 16, 2012
while in the case of Mars: the activity of some elementary life forms (beings) damaged Its atmosphere.

Holy smokes - where on Earth do you go to school that they teach you about alien lifeforms in class? I'm gonna call BS on that one.
Torbjorn_Larsson_OM
5 / 5 (2) Jul 16, 2012
@ jimbo92107:

"solar system rock is the source of earth's mountains."

We know it isn't, in so many ways. Plate tectonics makes upthrust mountains as plates meet. And plate tectonics are the source of the modern granite crust. It is easy to see by isotope analysis that Earth minerals differ from exogenous material.

@ Gaina:

"I knew very well that the main supplier of watter onto the Earth were comets."

No more than 50 %, though I believe 10-15 % is consistent with most studies.

"why similar processes of water accumultaion does not occur on oours nearest planets: Venus and Mars?"

It is as if you have read part of my comments and rejected the remainder. I walked through an encyclopedic source (FWIW, be careful with those) and gave its link even!
Torbjorn_Larsson_OM
5 / 5 (2) Jul 16, 2012
"The answer which I know from the school is ... while in the case of Mars: the activity of some elementary life forms (beings)".

No such text books are likely to exist, because this is not accepted science.

It isn't even recognizable science. Curiosity is on its way to Mars to establish habitability (looking for organics, since we have found water there), another thing you can check on Wikipedia. No known life there as of yet, either extant or extinct.

"The article and its discussion suggests that the problem of water on the planet Earth has a new feature"

Rather, it reverts to an old feature.

I still haven't looked at the research, but it seems from a better description the motivation was some analysis that found samples inconsistent with the modern theory of "not comet water". They did a new thorough analysis of samples returned by comet visiting crafts and found that the previous theory is still correct (i.e. comets can't be responsible for the majority of water).
GSwift7
5 / 5 (2) Jul 16, 2012
to barakn:

Feel free to apologize for being wrong any time. Nobody calls sulfur dioxide "anhydrous sulfuric acid."


Sorry, meant to say that the majority of "sulfur compounds" there are anhydrous. The majority of all compounds on venus are anhydrous, since hydrogen is only a trace gas there. Although many sources refer to the clouds on Venus as being made of sulfuric acid, that's actually outdated and a good example of sensationalism now. Current understanding is that h2s04 (sulfuric acid) only makes up a tiny fraction of the clouds, at the top of the cloud layer. s02 is found in lower layers of cloud. With the temperature/pressure on venus compounds which would not condense to form liquid or solid aerosols on Earth may do so in the cloud layers of venus. Sulfur literally evaporates on the surface, as does lead, tin and zinc.

Sources to follow in the next post, with quotes from the articles.
GSwift7
5 / 5 (2) Jul 16, 2012
http://www.outers...cid.html

Some clouds on Venus include sulfuric acid in their composition, although recently it has become known that sulfuric acid actually only makes up a small percentage of the clouds on Venus


http://hyperphysi...env.html

Early evidence pointed to the sulfuric acid content in the atmosphere, but we now know that that is a rather minor constituent of the atmosphere


http://hyperphysi...env.html#c4

Despite the ominous-sounding presence of the sulfuric acid, it is a very minor constituent in the atmospheric composition of Venus
GSwift7
5 / 5 (2) Jul 16, 2012
That's rather off-topic though. As for the subject at hand, the ratio of deuterium/hydrogen (D/H):

As I understand it, there's a 'cosmic abundance' for that ratio. Everywhere we look, it's the same, as though that were set at the beginning of the Universe. Even the majority of bodies here in our solar system share that ratio (Sun, Jupiter, Saturn, etc). However, that ratio is not present on certain objects, such as Earth, Venus, comets and asteroids (C-condrites). The big question is: why is the ratio on Earth different, and why is the ratio on Earth so similar to what we see on comets and asteroids? On Venus and Mars, D/H is even higher than here, so we guess that H evaporated into space faster than D did there, leaving higher D/H.

a good paper discussing it (with chemistry):

http://www.lpi.us...9038.pdf

I can't find any reference to the distribution refered to by guy in the original article on this page though. Has anyone else managed to find something?
GSwift7
5 / 5 (2) Jul 16, 2012
I've spent hours trying to understand what the press release is talking about, and I'm starting to wonder if the person who wrote the press release may have misunderstood something or paraphrased incorrectly a little? The pieces just don't add up for me. I don't see how they went from A to B to C and then say that it questions the predominant theories about how our solar system formed. Maybe some key piece was left out of the press release to keep it brief?
Gaina
not rated yet Jul 20, 2012
@ jimbo92107:

No more than 50 %, though I believe 10-15 % is consistent with most studies.
It is as if you have read part of my comments and rejected the remainder.

I would like to add the folllowing informations about presence of water in a classic Russian textbook (Dagaev,Demin,Klimishin, Charugin, Astronomy, 1983). "The water content in the Mars atmosphere 0.3%, O2 0.1%, on Venus: Oxygen 0.01%, water 0.05%. Are these quantities old or qualitatively incorrect?".

Russian astronomer G.A. Tikhov (1875-1960) supported the oppinion that a more important quatities of water could be in the subsoil layers of Mars. I hope that by this I have answered to http://phys.org/p...physorg/

as well.

Why we do not take into account the subsoils of the nearest planets?
SteveL
not rated yet Jul 20, 2012
Why we do not take into account the subsoils of the nearest planets?
Lack of samples? It was just a very few years ago that ice was found under the surface dust of Mars.

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