It seems like the big question to finding life outside of this planet is finding a location that has a source of water. But has anyone actually ever found water outside of Earth, proving it isn’t just an Earth based matter? And are we sure that potential extraterrestrial life would actually need water to survive? It seems like we are putting in a lot of effort into finding Earth-like planets, when life elsewhere could simply have evolved differently to be compatible with temperatures too hot or cold for us, and able to sustain themselves using different matters than we know of.
Will you accept ice as an alternate to water?
The answers are:
[ol]
[li]Yes, water is quite common in the universe beyond Earth. A lot is in the form of ice or vapor, but there is certainly liquid water elsewhere too (though perhaps not in the solar system). It is a big universe.[/li][li]Yes, so far as we know. All known life depends on water, and it seems unlikely, from our general understanding of chemistry, that any system of molecules complex enough to sustain life could exist outside of a water based system. However, I doubt that the possibility can be ruled out altogether.[/li][li]Hi Opal.[/li][/ol]
Life as we know it is found anywhere there is liquid water, including boiling hot undersea vents, nuclear reactor rods (or so I’ve heard), etc. Water isn’t necessarily the only liquid suitable, but based on what we find on Earth, scientists are confident (some extremely so) that planets which have liquid water will have life. Europa (one of the Galilean moons, at least) is thought to have an ocean of liquid water underneath an icy crust. One mission that was being looked at was to go there and drill through the ice and return a sample. There are myriad technical challenges of course, but if life were found, it would validate the theory.
There are a list of about seven things that people who spend a lot of time thinking about this have come up with as being necessary for life, which was devised as a response to a request to solve the problem of how would we recognize extraterrestrial life if we saw it. One of those things was some kind of liquid medium.
FWIW,
Rob
There is almost certainly liquid water in the solar system - under the ice of Europa, for example. Wikipedia has a whole page of places where liquid water is known or suspected at Extraterrestrial liquid water - Wikipedia
Are you sure they are really that confident? What would be the basis for such confidence?
The fact that life is found wherever there is liquid water on Earth is really no argument. Once life is established on a planet it is relatively easy to imagine how it might evolve to fill ecological niches, such as extreme temperature environments, very different from that in which it originally arose. However, we still do not know much at all for certain about how, or in what conditions, life first arose, and it may have involved a very unlikely chance event, or very special local conditions that would not arise commonly, even in watery environments. I do not see how anyone can honestly say that they are warranted in being “extremely” confident that life will arise de novo anywhere there is liquid water. (I do not say that no scientific expert has ever said such a thing, but scientists are as likely to be guilty of hype, and getting carried away by their enthusiasm, as the rest of us).
You want water beyond Earth? How about a star that has two enormous jets of water streaming into space?:
Hmmm? Of course it is. One might disagree with the argument, but one cannot deny that it’s a strong argument. It’s an excellent argument.
If an argument has been proven true, it’s no longer an argument. The fact that we haven’t managed to go there and prove it yet doesn’t mean that the argument is therefore nullified; it just means that it’s still an argument. It’s true in *all *environments so far that we can test; 100% of them, without exception. Arguing that it’s true in similar environments we haven’t tested yet is a long, long way from being “no argument”.
OK, it is an argument, but did you read the rest of my paragraph where I explain why it is a very weak argument (which is, of course, the colloquial meaning of “is no argument”). Extreme environments on Earth are a special case because they are adjacent to less extreme environments in which life already exists and from which it can spread. There is no reason to believe that that will hold for extreme environments elsewhere in the universe. Indeed, it almost certainly will not hold for most of them.
Yes it is!</python> (But seriously, yes it is.)
The most common element in the universe is hydrogen. Next is helium, but helium is chemically unreactive. Next are carbon, nitrogen, and oxygen. Therefore, the most common compounds in the universe are methane (CH4), ammonia (NH3), and water (H2O). There are thousands of giant balls of frozen methane, ammonia, and water floating around in our solar system alone.
A sample size of 1 isn’t statistically meaningful.
Taking evolution back to the earliest days, life is formed by random chemical reactions which generate new and complex molecules. Of those molecules, the ones which can maintain their form in the chaotic stew, survive. Then some of those molecules are expanded upon by the random reactions around them, with some percentage developing an ability to eat, self-replicate, or whatever. As time goes on, the molecules approach ‘lifehood’ as they continue to grow and gain sufficient complexity.
Now it’s entirely possible that carbon and water, for example, are particularly good building blocks, making it far more likely to coalesce into a more complex form. But it’s also possible that that’s only true in conditions like the Earth. On Venus, for example, there may not be much water, but that it’s sufficiently hot that some form of molten metal serves a similar purpose. And whereas frozen moons further out in the solar system do have water, they are too cold to have a sufficient quantity of regular, localized chemical reactions, whereas someplace like Venus is constantly stewing.
But it’s not a sample size of 1. It’s a sample size of thousands of extreme environments, many as extreme or more than Europa. There’s no logical reason to think that Earth has some unique status; I would argue that that claim requires some pretty strong argument.
There’s no reason to distinguish Europa from any number of hostile environments here on Earth other than a - natural, I admit - Earth-centrist view of the universe.
Any reason why life couldn’t take advantage of the other most common compounds: methane and ammonia?
It’s only a sample size of thousands if the question is something like “Could we get bacteria to grow on Europa?” I’m sure we could.
However, if the question is “Could life have originated on Europa?” then we are still left with a sample size of 1. There is no evidence that I’m aware of supporting multiple, independent sources of life on Earth. Even on Earth, life only got started once.
(In fact, I expect that we’ll someday find life on Mars and realize that it came from Earth, too.)
It’s possible, and Titan looks like it has some liquid methane lakes, so it’s a perennial candidate to host exotic life forms.
As for whether the existence of life on Earth means that life is very likely to form anywhere there’s liquid water, consider this hypothesis. Life in the universe is very unlikely to form, so unlikely that in the 13 billion years since the formation of the universe, there has been only one planet among the hundreds of quadrillions that developed life.
Now, if this hypothesis were true, then how would the inhabitants of the single life-bearing planet in the universe know? Obviously, if it’s true, we’d be those inhabitants. How can we tell the difference between a universe with only one life-bearing planet and a universe with quadrillions of life-bearing planets? The existence of life on our planet can’t be used as an argument for how common life is, because if our planet didn’t have life we wouldn’t be here to wonder how common life is.
We have to find other life-bearing planets to give us some real data. We have one sample, but that sample is biased by our sampling methodology and has to be discarded. So then we’re left with no samples, and therefore no real way to tell how common life in the universe is. We need to find some other samples, even one other sample, before we can make some guesses.
All life on Earth tells us is that life doesn’t violate the laws of physics.
Couldn’t it also be said that we are living in an extremely young universe? Suppose new life can emerge as long as there are new stars forming. Star formation should be ending at about 10^14 years. That means the universe is right now 0,01% of it’s life producing age. If the emergence of life was to be so rare that it would only happen once in the lifetime of the universe, wouldn’t it be far more likely for that intelligent species to observe a middle-aged universe?
Sure. But suppose you open the paper and find out that someone has just won the lottery. It’s pretty unlikely that you’ll win the lottery. So does that mean that the person who won the lottery must have played the lottery lots and lots of times? Or just once?
This sort of reasoning, from an already known outcome backwards to estimate the unknown probability of that outcome occuring, is known as Bayesian probability. Imagine you draw from an unknown deck of cards and pick the 2 of clubs. Without knowing how many or what kinds of cards there were in the deck, what can you say about the probability that you would pick another 2 of clubs if you drew again?
It is true that it seems like liquid water will exist in the universe for many billions of years in the future, and it is also true that life on Earth arose very quickly after liquid water formed on Earth. That gives us the feeling that, since life arose early in the history of the universe and the history of earth, life must be fairly easy to form. But we really need a few more unbiased samples here, and the existence of life on Earth is a biased sample.
We’re not talking about just drawing one more card. The situation is more like drawing a 2 of clubs, and then asking what is the likelihood of drawing at least one 2 of clubs if you draw another 10.000 cards. While we might not be able to determine a specific likelihood, can’t we say that 0 is a far less likely answer than something larger.
I’m assuming we have no reason to assume the 2 of clubs is more or less likely on the first draw than the subsequent 10k draws. It may be that life is more likely in a young or old universe, but as far as I know we don’t have that information.
I agree with your scenario. We draw a card, and it’s the 2 of clubs. Then we imagine drawing another 100 quadrillion cards from the deck. What are the odds that we’ll draw at least one other 2 of clubs? We know the odds aren’t zero (for the analogy to hold the draws are independent, meaning we put the 2 back in the deck). But since we don’t know the size of the deck, how can guess? Yeah, we’ve got 100 quadrillion more draws. But is the size of the deck 10 cards? Or 10^10,000,000,000,000,000?
I don’t have highly extensive knowledge of bayesian statistics, so bear with me if I’m saying something stupid. Suppose we have two cases:
Case 1: We draw 100 quadrillion cards. We know the 10th card is the first 2 of clubs. We have no information about the rest of the cards
Case2: We draw 100 quadrillion cards. We know the 50th quadrillion card is the first 2 of clubs. We have no information about the rest of the cards
Can’t we then conclude that in case1 the likelihood of picking at least two 2 of clubs is far greater than in case2. But we can’t actually calculate anything specific about the absolute likelihood?