"Hospitable" exoplanets and our conception of "life"?

Scientists have been thinking about such things for many decades. The fact is, we don't really know what extraterrestrial life might be like, and every serious SETI astronomer or astrobiologist would agree that we need to on the lookout for anything.

That said, we also have to keep in mind that right now, the only kind of naturally occurring life we know of in the Universe is carbon/water life existing on the surface of a rocky planet orbiting a yellow G-type main sequence star. So if we're going to look for other life in the Universe, the best way to start, at least, is by looking for life like our own, on objects like our own. In other words, it makes more sense to start with what we know can work by example, rather than to start with what may well NOT work given that we don't have any examples yet.

However, that isn't to say that our knowledge of both astronomy and biochemistry can't be put to use in narrowing the search. On the astronomy side, we have very good evidence that Jupiter's moon Europa has an ocean of salty liquid water under its icy surface, and since we know that there exists life in our oceans, including life that is fed by geothermal energy rather than energy from the Sun (on Europa, geothermal energy is the only option since the ice crust would block all the sunlight), we can state with a fair degree of certainty that some kind of life at least COULD exist on Europa. Furthermore, the tidal effects that in Europa's case heat the interior and allow oceans to exist may well be present on other gas giant moons orbiting other gas giants elsewhere in the Universe, and given that moons like Europa would not have the same kind of restriction on distance from their star that you have when trying for life on the surface, even gas giants very far from their stars could have moons with habitable interiors, and it is entirely possible that life in the Universe may be more common on gas giant moons than on rocky planets.

Alternative biochemistries have also been explored to some extent. The most likely sort of alternative biochemistry would be one that uses carbon like us, but a suspension medium that is not water. Ammonia (NH3) and methane (CH4) are both in the same family of compounds as water and could possibly serve as suspension mediums for life. There are also some compounds such as fluorocarbons which could serve this purpose as well. Unfortunately, most of these chemicals are only liquid at significantly lower temperatures than water, so life forms using them would exist only in very cold environments and thus would likely metabolize and grow much more slowly than our kind of life does, meaning in turn that evolution would act more slowly on them. Getting farther away from our own biochemistry is the idea of using elements other than carbon in order to form long molecular chains. Silicon is usually the most common proposal, since it has four bonds just like carbon and can form fairly versatile molecular chains, particularly when oxygen atoms are involved as well. However, most scientists suspect that silicon is probably too inert to support any kind of life. Sulfur and phosphorus have also been proposed as chain-forming elements, but these are even less likely than silicon. Finally, one of the most far-fetched proposals is to do away with molecular chemistry entirely and base life forms on electromagnetic forces acting in a plasma. It is known that plasmas can form organized vortexes with remarkably life-like properties, and it might be conceivable for such 'energy life forms' to exist in the atmospheres of stars or gas giants.

You can read more about these subjects on web pages such as the following:

http://en.wikipedia.org/wiki/Alternative_biochemis...

http://en.wikipedia.org/wiki/Planetary_habitabilit...

http://www.astrobio.net/

http://www.daviddarling.info/encyclopedia/S/silico...

http://ezinearticles.com/?Plasma-Life-Forms---Sphe...

http://people.msoe.edu/tritt/sf/europa.life.html

Gilese581d has been known about for years. Basically it probably has on average a just above freezing temperature temperature and only is able to support bacteria or the such. If you were to land there it would be like a giant allmost freezing swamp.

They are pretty much going for planets as close as ours, because since we know life is here there's a fair chance planets similar to use will have life.

Also if we do find intellegent life it will resemble us sorta, depending on the enviroment they may look like lizard-humans or insect-human form.

Don't get your hopes up though statistically speaking there are probably only 4 other intellegent species in our entire galaxy.

Looking at our history also more than likely they've blown themselves up by now.

We don't know what we don't know. Exactly how should we "look for" an unknown configuration of non-carbon based chemistry and demonstrate it is alive? Give me details.

There is a large storm on Jupiter called the Great Red Spot. We believe there are complicated chemical reactions which cause the Red Color. Is the Red spot alive? Why or why not. You must give not opinion but defensible facts proving that the non-carbon based chemistry satisfies a reasonable definition of "life" or it doesn't.

If you actually tried to do it, you'd find it wasn't that easy to do and almost impossible to do by robot with our current technology.

Ah! An actual thought-provoking question on here for a change!

Yes, I do think scientists are a little too narrow in their search for life. Life doesn't have to be carbon based or require water. But, as you said, life like this would be easier to find and understand. I also think our definition of "life" somewhat limits us to finding anything else that may be self-replicating. Because of this, we may miss out on discovering something entirely different.

OMG YES!!! i'm sorry finally someone has the same freaking viewpoint as I do too!

I have often wondered why scientists only look for potential life where conditions are 'right' as we define them. Who says that we are anythign special? Afterall is said and done, we're merely humans. We might be the "odd ball out" with a million other occupied planets that thrive on methane for heaven's sake lol. I agree. We're totally tottttaly limiting our approach (or they are).

And science is relatively new, so to speak,a nd I often question whether this is actually all true. Like who says one guy, einstein, or newton, what have you, can make up all the laws to the universe? science can explain a good amount of things, but it just can't explain everything. it might even be wrong. who knows. we don't lol. how can yo prove THAT?

First we need to define life, since we can't just go around calling everything "life". Does life think, or process information? Probably, or we can call every rock alive. Does it reproduce itself and pass on traits? Probably that as well. Life may require so many unlikely conditions that biological life may be the only one possible in this universe, and rarely even at that. Biological life based on hydrocarbons, since only these it seems are able to form into such complex chains as might be required for life.

I would have to concur with you. That is why it is up to my generation(the future) to privatize the space industry for that corporations are much more efficient at accomplishing tasks in a small amount of time because money is on the line.

Let's be honest, NASA says they HOPE to land on Mars by 2035. And knowing NASA they will have to delay it due to a minor malfunction in the secondary, X-535 Module that has a tube in it.

in effect they are limiting themselves, but that is on purpose. there is only so much time and money that can go towards the search, so instead of looking at everything, they concentrate on the ones that have the best chance to have life, yes, as we know it.

Please do not confuse what reporters report with what Scientists actually think. The reporter is trying to sell a good, interesting story - not report tha facts.

you mean like giant whales in neptune?