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SinisterF
2012-Jun-14, 03:16 PM
I've watched several documentary about life on in the Universe. All of them say that in order for a planet to have life it must follow some rules. One of the rules is that it has to have water.

Is it not possible to have life that can live with off of different elements?
If not then why?

Swift
2012-Jun-14, 05:21 PM
First, I have to get one nitpick off my chemist chest: water is a molecule, not an element. It is made of two elements: hydrogen and oxygen.

OK, I feel better. :D

As to your question, the simplest answer is "We Don't Know". It seems that any sort of chemistry-based life (as opposed to weird science fiction ideas like energy beings) is going to have to have some sort of solvent, and water is a pretty darn good solvent. And all the life we are familiar (on our single example of Earth) is based on water.

Among the things that make water so good is that it is a liquid in the range of temperatures that lots of chemistry takes place in, and a lot of materials are soluble in it. It also has some other nice properties, like ice is less dense than liquid water (so it floats on top, and ponds don't freeze from the bottom) - is this critical... maybe not, but we don't know.

Lastly, water is pretty common throughout the Universe, and we've seen it many places.

Is it conceivable that some other solvent, like liquid ammonia, could work? Yes, it is conceivable, and some people have speculated about the biochemistry in such liquids. But there is no evidence that these work.

Colin Robinson
2012-Jun-14, 11:56 PM
I've watched several documentary about life on in the Universe. All of them say that in order for a planet to have life it must follow some rules. One of the rules is that it has to have water.

Is it not possible to have life that can live with off of different elements?

The possibility of life containing liquid ammonia, instead of water, is the topic of an article

http://www.daviddarling.info/encyclopedia/A/ammonialife.html

in David Darling's Encyclopedia of Science. That article will link you to other online info.

Colin Robinson
2012-Jun-15, 12:37 AM
water is pretty common throughout the Universe, and we've seen it many places.

True, but other simple hydrogen compounds, like methane and ammonia, are also common.

What is not so common is for any of these compounds (including water) to be detected in liquid form. In this respect the Cassini mission accomplished two breakthroughs: finding the water geyser on Enceladus, and the methane/ethane lakes on Titan.


Is it conceivable that some other solvent, like liquid ammonia, could work? Yes, it is conceivable, and some people have speculated about the biochemistry in such liquids. But there is no evidence that these work.

It is true that no-one has discovered, or engineered, a life-form whose cell fluid is based on a liquid other than water.

On the other hand, there is quite a bit of evidence (from chemical laboratories, and industrial technology) to establish that other liquids can function as effective and versatile solvents -- they can dissolve a variety of compounds (including carbon compounds), and enable a wide range of chemical reactions to take place...

Ara Pacis
2012-Jun-15, 12:47 AM
Speculation, all of it.

Colin Robinson
2012-Jun-16, 06:43 AM
Speculation, all of it.

Ara, in the thread " 'Exo-life' or 'life in the universe' ", you agreed with Paul Wally's suggestion that "Perhaps we should use the term 'chemical complexity', then we can ask what the level of chemical complexity is on other planets and moons...Earth biochemistry is an example of chemical compexity in the universe".

Do you think it's a valid scientific question to ask what level of chemical complexity can occur in environments with a liquid solvent other than water, e.g. methane, ammonia?

Ara Pacis
2012-Jun-16, 09:01 AM
Ara, in the thread " 'Exo-life' or 'life in the universe' ", you agreed with Paul Wally's suggestion that "Perhaps we should use the term 'chemical complexity', then we can ask what the level of chemical complexity is on other planets and moons...Earth biochemistry is an example of chemical compexity in the universe".

Do you think it's a valid scientific question to ask what level of chemical complexity can occur in environments with a liquid solvent other than water, e.g. methane, ammonia?Do whatever you want. Doesn't make it non-conjectural.

Colin Robinson
2012-Jun-16, 08:38 PM
Do whatever you want. Doesn't make it non-conjectural.

Regarding chemical complexity on Titan, we earthlings could do more than conjecture.

The Huygens probe showed that a soft landing is feasible with current technology, even though Huygens itself wasn't equipped to keep functioning for any length of time after it landed.

NASA is considering a mission called TiME -- Titan Mare Explorer -- to splash down on a hydrocarbon lake, float around, and test the lake's composition. This sort of thing can be done. It is a question of will and resources...

potoole
2012-Jun-16, 09:14 PM
Was it Titan or Triton that Hugyens (Huygens) :eek: landed on?

PO'T

Colin Robinson
2012-Jun-16, 09:19 PM
Was it Titan or Triton that Hugyens landed on?

PO'T

It was Titan.

I don't think any probe has been landed on Triton as yet, though Triton has been observed from space.

potoole
2012-Jun-16, 09:33 PM
Titan, thanks.

Aren't temperatures on that 'moon' very, very cold? So cold that chemical reactions would happen very, very slowly? Perhaps too slow for the organic (generic name organic) chemicals, which the atmosphere and liquid lakes are composed of, to chemically react, much less evolve into some sort of life form? Unless, maybe, catalysts were involved.

Just wondering
PO'T :)

Colin Robinson
2012-Jun-16, 10:46 PM
Titan, thanks.

Aren't temperatures on that 'moon' very, very cold?

Yes, in comparison with Earth, Titan's surface temperature is much lower. That is why methane on Titan can behave like water on Earth, forming rain, rivers, and lakes.

I've used the words "surface temperature" for a reason, which I am coming to...


So cold that chemical reactions would happen very, very slowly? Perhaps too slow for the organic (generic name organic) chemicals, which the atmosphere and liquid lakes are composed of, to chemically react, much less evolve into some sort of life form? Unless, maybe, catalysts were involved.

It's true that chemical reactions are slower at lower temperatures. This point often gets mentioned as an argument against Titan having life.

The speed of reactions can be increased by catalysts, but how would the catalysts come to be there?

Well, it is known that complex organic molecules are generated in the upper atmosphere, whose temperature (like that of Earth's ionosphere) is different from the surface temperature. These substances then precipitate down to the surface.

If the upper atmosphere, even occasionally, generates molecules with catalytic properties, these could enable chemical processes to get started in the lakes.

potoole
2012-Jun-16, 11:42 PM
Colin Robinson
Well, it is known that complex organic molecules are generated in the upper atmosphere, whose temperature (like that of Earth's ionosphere) is different from the surface temperature. These substances then precipitate down to the surface.

If the upper atmosphere, even occasionally, generates molecules with catalytic properties, these could enable chemical processes to get started in the lakes.

Thank you. Very interesting