Hi all! I’m new. Don’t have anything to add to that, just thought you’d like to know. Anyway, to the topic at hand:
I’ve been thinking about extraterrestrial life lately (partly because I want to write a novel about aliens), and was thinking about ways in which life on distant planets could function differently from life on Earth. (For example, organic materials on Earth are carbon-based, but some wonder if life on other planets could be based on other Group 14 elements, such as silicon.) This led me to wondering about water. Does anyone know what kind of environment, if any, would make heavy water (aka deuterium: water where the hydrogen atoms have a neutron as well as a proton) more prevalent than light water (aka protium: the ordinary water that we drink, where the hydrogen has only a proton and no neutron)? Pure heavy water can be created, but it doesn’t occur naturally on Earth. On Earth, deuterium is always present in ordinary drinking water, but in extremely small amounts. What I’m wondering is, are there any combinations of environmental properties (i.e. atmosphere, air pressure, temperature, magnetic field, electric field, what-have-you) that would reverse this tendency, and make deuterium more naturally prevalent than protium?
Both normal hydrogen and deuterium are essentially entirely primordial, meaning dating back to the Big Bang, so their relative abundances would be the same everywhere in the Universe. The best you could hope for would be some local phenomenon that tends to sort them out, so you’d get a small pocket of deuterium set aside from a whole lot of normal hydrogen. The best bet I can see for this would be an extremely high-gravity world, with deep oceans, and stable temperatures in the vicinity of 4 or 5 Celsius: The bottoms of such an ocean might be predominantly heavy water.
Yes, but there must be some reason why most hydrogen on Earth is protium and not deuterium, and I’m wondering what conditions account for this and what conditions would reverse their proportions. Is it chance? Would some other planet have more deuterium simply because that’s what it got? Or does deuterium lose its neutron easily (not by decay, but perhaps by bombardment) so that it’s rare in nature? If this is the case, what conditions would allow it to keep its neutron for a longer period, or give hydrogen a propensity to attach to neutrons?
This topic is becoming like an itch that I just can’t scratch… I wish I had a chemistry major!
The reason most hydrogen on Earth is protium is because the Earth shares the same ratio of protium:deuterium as the rest of the universe. It’s like scooping out a bucket of sea water - you’ve got about the same amount of salt concentration as the rest of the ocean because that’s where it came from.
I’ve been reading even more. According to a Yahoo!Answers question, deuterium is more prevalent on Venus. An answer as to why was that Venus started out with an extremely high abundance of hydrogen, and its high gravity kept deuterium (twice as heavy) in the atmosphere while protium could escape.
So. Perhaps my alien planet could be one that started out with an absolutely massive amount of hydrogen, and also had a gravity that would let most protium escape while leaving most deuterium behind? Although the answer also said that this effect would be negligible on water — except that she only referred to H2O and HDO, not D2O. So…I still have research to do…
What I’m really looking for is a planet where heavy water is so prevalent that life evolved to depend on it in the same way that we depend on regular water. Is this scenario at all plausible?
EDIT: Hey… How come I can edit this post but not the two previous ones?? O.o
Sorry for the double-post… I couldn’t edit my first two posts so I didn’t know that I could edit the third one…
Well, that’s what I thought. Thanks for the clarification, though! Do you know if any planet could have conditions that would make deuterium more common, though?
The proportion of hydrogen that is deuterium might be larger on Venus than it is on Earth, but it’s still pretty small. I don’t think there’s any place known in the Universe, outside of a laboratory, where deuterium is more common than normal hydrogen.
I’m not a biochemist, nor do I play one on television, but – doesn’t deuterium have the same chemical properties as hydrogen? So, if there were a pocket of the universe where deuterium predominated, wouldn’t all the biochemical processes of life go on just the same as they would with hydrogen?
Of course not. It’s not exactly the same as hydrogen, so by definition it doesn’t have all the same chemical properties. Deuterium forms stronger hydrogen bonds which are harder to break, and in the case of heavy water, this can disrupt normal reactions in cells. Heavy water in eukaryotes can cause sterility at 25% substitution and death at 50% substitution. It halts cell division by disrupting the mitotic spindle formation.
There could be some hypothetical biological mechanism that could use deuterium and heavy water instead of hydrogen and light water, and on the surface these mechanisms might even look identical to those of Earth organisms — but they would differ on the chemical level. That’s why I’m intrigued by the idea of my aliens coming from a planet abundant in deuterium and heavy water — I get to demonstrate how Earth isn’t “special” (i.e. these aren’t the only conditions in which life can exist), AND I get to invent new biological mechanisms! :D!!
Unfortunately, all known methods of producing pure D2O require cascading- taking the slightly enriched output of a single step and using it as the starting material for another step in the enrichment process. It’s extremely unlikely this could ever happen naturally.
A planet would have a much higher ratio of heavy water if a sentient specie put it there, naturally.
You can justify this by stating a very, very advanced race needed an abundant supply of Deuterium, and therefore engineered moss/fungi/algae/nanites to do it for them. They released them on a cluster of systems, planning to come back in a few million years when they’re ripe (after all, it’s cheap, systems are plentiful, and sparcely populated), or as an experiment.
A billion years later, the project long since forgotten and deuterium no longer needed in their technology… Bam. Life. Naturally…
Everything I’ve ever read about isotopes says there chemical properties are the same. I could understand that, with something like hydrogen, where the difference in isotopes is much bigger, and thus the chemical properties are more divergent, but I wouldn’t castigate someone for not knowing that.
Heck, I know science books where an isotope is defined as an element with the same chemical properties, but a higher mass due to addition of neutrons.
Changing hydrogen to deuterium strongly affects reaction rates (kinetic isotope effect). The effect is especially pronounced in hydrogen because the mass is doubled in deuterium, it is much smaller in heavier elements.
You can notice that, e.g. when growing bacteria in D2O, instead of H2O, they generally grow slower.
I didn’t seem much different from normal water to me, except for the slightly higher melting point (it freezes around 4 degrees). I once put a D2O solution in a fridge that was somewhat colder than usual and the D2O solution froze first.
But if you just look at a bottle of it it looks like ordinary water, just more expensive.
A pint (UK) of heavy water would weigh about 2 oz more than a pint of ordinary water, but you could easily miss a small detail like that. Much the largest fraction of the weight of water comes from the O; the H[sub]2[/sub] is trifling by comparison.
That’s an interesting idea, Todderbob, but by “naturally” I meant through purely abiotic processes. Without any purposeful interference by a living being, ESPECIALLY not an intelligent one. But I think I just might use a similar idea for something else, if I think of one.
I do, however like the idea of a moss/fungi/algae/some other non-sentient living being somehow producing a bunch of deuterium…I’m going to look into that…
But what I’m really looking for is a situation where heavy water, rather than light water, would be the foundation of ALL life, just as light water is the foundation of all life on Earth. So the fungi/algae/moss wouldn’t be there, yet…
Well I’ll be damned. That’s basically what my Apple Dictionary and what Wikipedia say, too. Huh. I just figured that since there’s a difference in the number of subatomic particles then this must somehow lead to at least a tiny difference in chemical behaviour. But you’re right, this must not register in any significant way with heavier atoms. It probably only affects hydrogen and a few other light atoms.
And sorry about the “castigating”. Sometimes I feel a need to get like that…don’t know why… ><
P.S.
In my last post, I couldn’t get the “chart” into an easily readable form, whether I used spaces or whatever… And now my editing time has expired for that post. Forgive me my lack of BB code knowledge…
Hmm. Maybe I’ll try again and just use periods to space them out. XD