I have a question!

[Outbackmanyep]

Hey all!

As i am more interested in comets than anything else, i was reading a book on comets and one section i read was going on and on about D:H ratio's measured in comets.

Deuterium to Hydrogen ratio....

Can anyone enlighten me on why anyone would want to know what D:H ratio's are??

I'd like to understand why comet scientists would want to know this for!

Appreciate any answers!
Cheers!

[[1ponders]]

Part of the reason is to try to determine where all Earths water came from. One theory is that it is predominately Cometary in origin. Unfortunately the D:H ration of water on Earth is different to the D:H ratio of currently observed Comets.

However latest reseach seems to indicate that in the early solar system there were cometary type bodies in the inner solar system that had a different D:H ratio to the outer system Kuiper belt/Oorte cloud bodies. These inner "comets" may have been the source of earthly water.

Another reason is that the D:H ratio also gives an indication of the conditions in the developing solar nebula. Because Deuterium is more massive than H it would be more likely to be found closer in to the center of the developing solar system. Therefore it's distribution helps to explain mass, temperature and density conditions in the developing solar nebula

[Outbackmanyep]

Thankyou Paul for that insight!
So thats another reason to research comets, if we find a comet that has a D:H ratio similar to that of earth then its possible that those comets could have been a source of terrestrial water!
Quite interesting....

Has there been other molecular interstellar clouds that have a D:H ratio similar to Earth or our solar system??

[[1ponders]]

I'm sure there is, though I'm not aware of any in particular.

The composition of gas clouds throughout the milky way is not homogeneous. From my understanding of the process, deuterium ions are formed during nucleosynthesis in stars (apart from that formed about 2-3 sec after the BB up until about 3 minutes after the BB, though most if not all of the earlier deut would have been destroyed by high intensity gamma radiation). Deuterium is basically a proton and a neutron and is an intermediary product in the process of producing helium, . If this stellar deuterium can make it out of the core where nucleosynthesis is going on, it has the chance of making it out of the star altogether, eventually joining with an electron and forming a deuterium atom. This "leaked" deuterium contributes to the total deuterium mass in a given gas cloud, however apart from the BB stuff the next major source is from supernova explosions, where huge quantities of deuterium is believed to be produced.

So the long and the short of it is, the concentration of deuterium that may collect to become water>ice in comets in a stellar nebula varies depending on the output of stars seeding surrounding gas clouds and the resultant product of any supernova in the area along with variations in the distribution of the original BB deuterium.

[Doug]

Interesting subject. Given the amount of water on the Earth (NSW excluded), either the water bearing comets were huge things, or there were heaps of them. If there were heaps of them, the other planets , Venus and Mars should have been soaked as well, and retain massive deposits of water. Even the moon should show evidence of once having had copious quantities of water. If they were few in number, but large in mass, there ought to be clear evidence of the cataclismic impact/s I would think. Something like an E.L.E. except pre watered Earth would have no doubt been clear of life.
Is there any serious theory that explains why water would have been more or less confined to comets, and not evenly distributed throughout the Solar Sstem?
Doug

[[1ponders]]

It's a pretty volatile subject amongst some scientists Doug. Only time will tell how it turns out and who was right. If you are interested there is a book called "Atom: A Single Oxygen Atoms Journey from the Big Bang to Life on Earth and Beyond" Lawrence M Krauss (http://www.phys.cwru.edu/~krauss/). It is a great read. It's not a text book but describes the formation of ......everything....in laypersons terms. Just my sort of book :)

[Doug]

Thanks Paul, I 'll see bout getting a copy; looks like I'll have to go thru Amazon. I like the tone of his open letter to the Pope, though he could lighten up a bit on the other Cardinal.
Cheers,
Doug