how do we know?

magicrules22311 · Jan 6, 2006

We think that water is required for life, since it is needed on the earth. Now why do they(scientists) think that on COMPLETLY different planet, water is needed for life? I mean, its even possible that weird animals from different planets require lava or even some strange substance that doesn't even exist on our planet to live. I think its kind of stupid for scientists assume that planets need to be like earth to support life. (sorry for my spelling, im use to talking to people on AIM)

bonzelite · Jan 6, 2006

+1 i agree.

Saiph · Jan 6, 2006

well the main reasons are: all forms of life here require water. And we know some extreme life forms. Basically anywhere we find liquid water, we find life (even in boiling heavily toxic water sources...assuming said source is like that a long time). So, that's why we look for life in those areas. There may be a life form that doesn't need it...but it isn't nearly as probable. So we look at the probable locations first. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

scull · Jan 6, 2006

We need carbon.

qso1 · Jan 7, 2006

Scientists do not assume that life needs water, they will clarify in all the scientific literature I have read by using statements like "Life as we know it" or that they believe life requires water because earthly life is all we have to go by at the present time. And it is not stupid to search for planets we already know have the potential to be life bearing. After all, the ones in this solar system do not look too promising based on available data to date. We haven't even been able to say Mars has life despite the initial results of the Viking probes and these worlds are right next door compared to extra solar worlds. And...if they look at a planet like 51 Pegasi B and see evidence for life in the spectral data, they will announce that they are surprised but they will look at everything possible. It just makes more sense to look at Earthlike worlds first. Right now we are still unable to detect E worlds anyway. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

dragon04 · Jan 7, 2006

I'd be remiss to say it's impossible for ANY type of life to exist that doesn't require water, but it sure is the most convenient liquid. I can't say with total surety that some animal couldn't have lava for circulatory fluid, but at the temperatures at which lava exists, I can't imagine a biology consisting of the known elements that could contain it in a circulatory system on a susatained basis let alone build a complex biological framework around it. Silicon based life forms might perhaps be a possibility, but their metabolism would be very slow. I think the smart money is on good old H2O if we want to discuss the commonality of life in the universe. <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

bonzelite · Jan 7, 2006

if my memory is correct, some bacteria thrive off hydrogen only. it's at least a good start away from traditional metabolism.

dragon04 · Jan 7, 2006

They thrive off of hydrogen metabolically, but what's the goo inside the cell wall made of? <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

yurkin · Jan 7, 2006

Alternative Biochemistry “In addition to carbon compounds all currently known terrestrial life also requires water as a solvent. It is sometimes assumed that water is the only suitable chemical to fill this role. Some of the properties of water that are important for life processes include a large temperature range over which it is liquid, a high heat capacity useful for temperature regulation, a large heat of vaporization, and the ability to dissolve a wide variety of compounds. There are other chemicals with similar properties that have sometimes been proposed as alternatives.” For carbon based life I think ammonia is the only realistic substitute to waster. They do mention methanol, hydrogen sulfide and hydrogen chloride as remote possibilities.

bonzelite · Jan 7, 2006

drag, i did say it was a good START away from traditional metabolism <img src="/images/icons/wink.gif" /> indeed, they're water-based cells.

Philotas · Jan 7, 2006

all forms of life here require water. And we know some extreme life forms. That`s no argument. <img src="/images/icons/wink.gif" /> The main arguments against is the special properties that water has, and that other liquids doesn`t. <div class="Discussion_UserSignature"> </div>

unlearningthemistakes · Jan 7, 2006

there is a bacteria that thrives in Ar ( arsenic ) and doesn't need oxygen. Cecil textbook of medecine: 15th edition Beeson, Mcdermott and Wyngaarden ISBN- 0-7216-1683-1 or try the search engines of google and yahoo. <div class="Discussion_UserSignature"> pain is inevitablesuffering is optional </div>

unlearningthemistakes · Jan 7, 2006

well, speaking by experience, I don't believe we have seen enough of the scenario to say that simple life (I'm talking about bacteria) will always require water/oxygen. in life/biology, surprise is an element natural to the study. we still need to explore more before we can conclude that life has an arbitrary pattern. In cases of complex life, like us/plants/animals, water and oxygen are certainly essential. But do you know there is a plant that can subsidize/live with poisonous Ar?? it is the chinese ladder fern: Pteris Vittata Linaeus. <div class="Discussion_UserSignature"> pain is inevitablesuffering is optional </div>

mikeemmert · Jan 7, 2006

Hi, Saiph; I've been browsing around on Wikipedia this afternoon and have found they've updated the article on Titan a little: http://en.wikipedia.org/wiki/Titan_%28moon%29 Your comment about looking at the probable locations doesn't take into account where we can reach with the equipment we have. Wikipedia (which can be edited by anybody and is edited back very rapidly if vandalized) seems to think there's no way there's life on Titan, but I don't know about that yet. There's a piece of information I cant' seem to find, and that's the solubility of hydrogen in methane. Both are nonpolar compounds which are limited in what disolves in them. Possible life on Titan would be very primitive and would mostly live in the dense atmosphere there. That atmosphere contains methane (1.6 %) and some other compounds, including cyanogens, carbon dioxide which should have frozen out onto the surface and carbon monoxide, which is liquid at the appropriate temperatures. CO and CO2 provide oxygen, so there is carbon, hydrogen, nitrogen, and oxygen in that atmosphere. The methane shouldn't exist under the relentless UV light of the sun. And, what's more, the article states that Titan spends some of it's time outside Saturn's magnetosphere and so is exposed to particulate radiation from the solar wind. These could be the energy sources if the smog on Titan is a primitive life form. All Huygens really did is collect the smog and heat it up. Ammonia and cyanide were given off. So the smog contains some considerable amount of nitrogen (there was a link to that in a post a few weeks ago from ESA, I'll edit this post when I find that). Could the smog be some unrecognized bug that eats hydrogen and organics and converts them back into methane? Volcanos have been seen on Titan, but I would like to see quantitative measurements to see if any met

Saiph · Jan 7, 2006

considering that space programs run on a compartively very limited budget, if we wish to search for life, we should go to the most probable locations first. As of now, those locations are ones which contain liquid water. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nathanielyork · Jan 7, 2006

All of water's special properties that have been posted are important, and also the fact that the solid form of water (ice) floats in water, allowing animals to continue to live in bodies of water when the top is frozen over.

mikeemmert · Jan 7, 2006

<blockquote>In reply to:<hr />space programs run on a compartively very limited budget<hr /></blockquote> Increase the budget!

mikeemmert · Jan 7, 2006

I think this debate can be sharpened up and clarified by examining the fallback position if the solution in my last post doesn't work (i.e. the Dover School Board gets elected to Congress). That means we have a choice between a mission to Titan and a mission to Europa. It appears that the ice on Europa is about 20 km thick and covers the whole moon. I don't think much sunlight can get through that and I know particle radiation can't. In addition to water (maybe) life needs energy (certainly). So the dilemma is that Europa has water and Titan has energy. I think an energy source might be more important than the chemicals involved. One example of life not-quite-as-we-know-it would be an ecology that is not based on chlorophyll. It may very well be that chlorophyll came to prominence on Earth out of sheer, blind luck. There are a vast number of photochemical reactions which store enery. These will either go to completion or some way will turn up to use the stored energy, which would lead to recycling. I think we need to look for evidence of recycling. Like some chemical that exists where it shouldn't. Oxygen in our atmosphere is a known indicator. Methane on Titan's atmosphere might or might not be an indicator, but I think it's worth checking out. I know all about black smokers but I'll let you make that point.

zer01zero · Jan 8, 2006

Ok, So, what is YOUR evidence that there is life "on a COMPLETELY different planet" that doesn't require water. To that end, I think that it is foolish of you to make the statement "I think its kind of stupid for scientists assume that planets need to be like earth to support life."without backing up your statement with even the smallest bit of evidence. Come on mate, give people some credit.

Philotas · Jan 8, 2006

He isn`t claiming that there is life based on something else than water, just that it`s narrow minded to think life only works with water when we haven`t been looking for life on exotic places. <div class="Discussion_UserSignature"> </div>

bonzelite · Jan 8, 2006

"I think its kind of stupid for scientists assume that planets need to be like earth to support life." +1

mikeemmert · Jan 8, 2006

I would have to agree with Philotas here. No claim that there IS exotic life has been made, simply that we should look. Some examination has been made of Titan. I would like to see another mission armed with an electron microscope. I don't think Huygens has ruled out the possibility of life, although it certainly hasn't ruled it in.

zer01zero · Jan 13, 2006

Alright, you caught me on a bad day. I apologise for jumping down his throat. But I really think that if people wish to learn or pose ideas they should do it in a less aggressive manner

dragon04 · Jan 13, 2006

He isn`t claiming that there is life based on something else than water, just that it`s narrow minded to think life only works with water when we haven`t been looking for life on exotic places. It's not so much narrow minded as it is practical. It seems intuitive to me to search for the more probable than the less probable. To me, looking for exotic life forms in exotic places is getting the cart ahead of the horse. If I'm going to spend my vacation time and money prospecting for gold for example, I probably won't vacation in the Bayou. <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

mcbethcg · Jan 13, 2006

I am not a chemist. But what I have read, in literature about the possiblility of alien life, is that the complexity we see in higher life forms on earth require a vast number of chemical combinations and interactions. Imagine how many types of protiens, enzymes, hormones, interactions etc are required to make a human being function. The possible interactions between hydrogen, oxygen, and carbon are incredibly huge, primarily due to the characteristics of carbon, which has the ability to connect to a rather large number of other atoms simultaneously. For this reason, I think it is entirely possible that life may be possible with other chemical compositions, but it will probably have a slower, less effective metabolism, and probably be more simple. In addition, cold climates would have less energy available to drive life processes. For example, if there are seas on Titan, they may contain large, simple bacteria. I wouldnt think there would be much more. I would completely rule out creatures that live in extreme hot fluids like lava, for example, because the interactions between materials high temperature liquids are supposedly relatively simple.

how do we know?

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