[Flipside]

http://www.bbc.co.uk/news/science-environment-30414519

Basically, the composition of the ice taken in samples by Rosetta is different to the composition of the water on Earth.

Of course, this doesn't rule out the theory completely, since one Comet does not a thorough investigation make, and we have little idea of 67P's history, but it does deal it quite a serious blow.

[Mongoose]

Sweet, awesome Philae science already!

[Bobboau]

and the thought that being bombarded by solar and cosmic radiation for 4 billion years doesn't seem like a reasonable explanation for this discrepancy?

[Ghostavo]

and the thought that being bombarded by solar and cosmic radiation for 4 billion years doesn't seem like a reasonable explanation for this discrepancy?

Not unless that explains where the additional neutrons come from.

[Bobboau]

do you know what the solar wind and cosmic rays are composed of?

[Flipside]

You know, it'd be bloody ironic if, of all the millions of cometary bodies orbiting the Sun, we happened to land on a captured one from another solar system...

Edit : Though, in hindsight, it would also be kind of awesome.

[Ghostavo]

do you know what the solar wind and cosmic rays are composed of?

Electrons and protons mostly?

[Bobboau]

yeah, and neutrons, and other ions, all moving at high energy. I'm not a nuclear physicist but I would like to see an analysis of why this would not explain the higher concentrations of heavy water.

[Ghostavo]

Wouldn't you need free neutrons instead of neutrons present in atoms to do that?

[Klaustrophobia]

yeah, and neutrons, and other ions, all moving at high energy. I'm not a nuclear physicist but I would like to see an analysis of why this would not explain the higher concentrations of heavy water.

NEUTRons are not ions, they are neutral.  They are not accelerated by the sun's magnetic fields and therefore not ejected into space as solar wind.

[Flipside]

It's possible different types of ice formed depending on conditions in that specific part of the Solar System at the time, it's always possible that the comets that Neptune affected formed in a different area, or at a different time to 67P. Maybe this is one that formed slightly nearer the Sun, where more of the lighter isotopes had orbited out further (or possibly vice-versa)?

[Bobboau]

yeah, and neutrons, and other ions, all moving at high energy. I'm not a nuclear physicist but I would like to see an analysis of why this would not explain the higher concentrations of heavy water.

NEUTRons are not ions, they are neutral.  They are not accelerated by the sun's magnetic fields and therefore not ejected into space as solar wind.

other than "electrons and protons mostly", like ionized helium.

[watsisname]

As I recall, the general consensus (before Rosetta mission) is that comets delivered some of Earth's water, but not all of it.  The D/H ratios are somewhere in between what you'd expect from comets vs. a more sunward origin.  But there is a lot we still don't understand about the structure of the presolar nebula and how D/H ratios relate to it, or even if such a mapping should be so straightforward.

[watsisname]

yeah, and neutrons, and other ions, all moving at high energy. I'm not a nuclear physicist but I would like to see an analysis of why this would not explain the higher concentrations of heavy water.

Direct neutron capture cannot explain observations of isotopic ratios.  If it is from the solar wind, then you'd expect an inverse square law, with higher D/H ratios at smaller orbits.  This is not what we observe.  Cosmic ray origin doesn't work either, because then enrichment would be uniform over the entire region.  You would not observe any fractionation.

The fractionation instead occurs by a different form of processes -- physical, not nuclear -- where one isotope is more or less favored in that process than another.  For example, sublimation and crystallization, at different regions/temperatures of the presolar nebula.  Nuclear physics involving direct capture just isn't very important.  Think also of the carbon isotopic fractionation in plants.