How far from Earth can we say for certain that there is no life besides our own?
Posted Feb 12, 2012, 10:39 AM UTC
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The scientific consensus is that there's no life on the Moon. Beyond that, it's an open question. Mars may yet be a candidate for microbiological life underground (although not on the surface), and there are other locations in the solar system that could harbor life, such as Europa.
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For anyone who wants a brief run of the potential life candidates in our solar system, NOVA has a great video here. Called finding life beyond earth.
http://video.pbs.org/video/2157407032
They'll run through the three requirements for life as we know it, and where we may find them.
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Would it be safe to say there is no life on Venus or Mercury?
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The consensus for Mercury is that there's no life, for the same sorts of reasons as on the Moon and Mars: it's arid, has a minimal atmosphere, and has even greater temperature extremes.
Venus is more complicated since it has a rich atmosphere. Someone else in the thread linked to this.
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Mercury does have some pockets that are perennially shaded, there is frozen water in some. However, I think they are way too cold.
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The Mars Labratory Lander will land in 8 months and will prove within a half year if theres life on mars or not. The methane in the atmosphere would suggest that there is life there.
A scientist Bill Stone has plans to send a probe to the moon Europa some time soon (depending on funding) Check out his TED talk.. Its very good.
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How is the rover capable of disproving the existence of life on Mars?
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Well, the planet is geologicaly dead, unlike earth wich have volcanoes. So the big question is why there are methane in the atmosphere when the geology isnt the reason. Bachteria in the ice underneath the surface is most likely the answer. Thats the first thing the Rover will check out. If it doesnt find bachteria in the ice, theres probably not life on mars.
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The prior poster made an unsupportable claim. In science, it is only possible to support an idea using evidence, never prove an assertion beyond later refutation, and for the majority of ideas, proving a negative is impossible and therefore a logical fallacy.
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The prior poster
At first I thought you were talking about my comment, until I realized you probably meant perfektsirkel - why not just use names, that's what they're for!?
But either way, your comment is actually somewhat wrong-headed - not that it's false per se, but rather that its implications are different from what you seem to think.
What perfektsirkel wrote is reasonable as long as it is understood that scientific conclusions are provisional, as you point out. For example, one might reach the conclusion that there's no life on the surface of Mars based on e.g. the lack of water, as found in the study I linked to. Combined with a unsuccessful search for evidence of life, it would be a reasonable scientific position to conclude, as we have done for the Moon, that there's no life on the surface of Mars.
At that point you're just quibbling with perfektsirkel over the use of the word "prove", so it's no longer a question of an "unsupportable claim", just a somewhat poorly stated one.
The second problem with what you wrote relates to "proving a negative is impossible and therefore a logical fallacy". In this case, we actually have a deductive argument which has to do with the nature of chemistry and the necessity of water (or some equally reactive molecule) in order to support life. Finding good evidence of a long-term absence of water on the surface of Mars - as the study I linked to did - is similarly good evidence to support the hypothesis that there's no life on the surface of Mars. One can certainly prove a negative in a deductive argument, here's how it looks (simplified):
- Life exists on a planet if and only if water is present
- Water is not present
- Therefore life does not exist on that planet
Voila, I have proved a negative.
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I suppose we could go as far as to rule it out with great certainty, so I was just honestly asking what the rover's capabilities might have been to make such large claims.
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Well Voyager1 is about 1.0E+10 km from Earth, and may have some level of microbial contamination, so we've probably contaminated at least that far out!!
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i'd say that counts as "our own" life. since it came from earth so recently.
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Perhaps you meant intelligent life, or complex organisms ? Microbe spores can stay viable in space, especially if shielded from radiation. For nearby locations (karman line through mars), a big challenge is to show that this is not introduced from Earth.
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There is very likely life on the moon from the stuff we left up there (how active it actually is I don't know). There are airtight bags that have feces in them, urine, probably a good amount of mold spores and such that are shielded from solar rays.
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I guess that depends on your definition of "certainty".
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Pretty sure this is a good candidate for life on another planet.
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Absence of evidence is not evidence of absence. In the process of improving our ability to observe the universe, we discover things we didn't know that we didn't know. e.g. what is dark matter? To answer your question: There could be life under the surface of the moon. There could be aliens amongst us.
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I've always hated that cliched saying. Absence of evidence damn well is evidence of absence. Depending on the circumstances and how hard you looked it may not be particularly good evidence, but it still tells you something.
An accurate version would be: "absence of proof is not proof of absence".
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Absence of evidence damn well is evidence of absence.
That's statement is not logical. Just because something eludes your powers of detection, it doesn't mean that you have conclusively proven that it does not exist. You cannot draw a definitive conclusion. In the context of the OP's question, alien life can be present even if you haven't detected it.
You could say, extraterrestrial life probably does not exist within our Solar System, because we haven't seen any signs of it so far, despite decades of scientific observation. But you cannot be certain.
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So if you can't prove there is an apple in my hand there might be an apple in my hand?
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In fact, absence of evidence is evidence of absence. The linked essay explains why in more detail, but to intuitively understand why it helps to look at the most extreme cases. For example, the lack of evidence for the Ten Plagues is evidence for their absence, because if they had happened we'd expect to see a lot in the archaeological record. Similar remarks would apply to say Ancient Alien claims.
In general, absence of evidence is often a very weak form of evidence of absence, but it is still evidence.
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Well you could say with certainty that there is no life on the Sun or any other star in the universe.
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Hijacking. One thing is to have an open mind, but this is just ridiculous.
What we know as life demand some sort of molecular complexity. Sure, you could say that you could make life with a couple of hydrogen atoms and a magic wand, but that would be just as silly as acknowledging that god could wake up one day and populate the stars with his new pet bacteria just because he wants to troll us. At the end, stars are big fucking nuclear reactors that will rip apart any kind of complex structure you try to bind together.
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|What we know
My point exactly.
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Well, if you'd like to speculate about the life of sub-atomic particles, then good luck.
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very very unlikely
proclaim that life cannot exist
What do you see as the distinction between those two positions? What standard of knowledge do you consider high enough to say something "with certainty"?
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I don't see any distinction. From what we know life that can live on a star seems incredibly unlikely. But I don't think we know anywhere near enough to make a blanket statement that life in some form cannot exist on a star.
How much do we need to know? I'll let you know when we get there. :)
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What is life? There can be life in space in forms we can't even imagine. Nothing can be said for certain.
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"Life" is pretty well defined.
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not really, viruses are not considered alive by many classical definitions. it can get pretty obscure.
kubarotfl isn't really making any sort of point though
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viruses are not considered alive by many classical definitions.
Do you believe they ought to be?
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they are considered alive by some more modern definitions. there isn't a clear place to draw the line, different groups put it different places for practical reasons.
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why do you say no life between earth and the sun? venus is really complicated, all different temperatures and conditions in it's atmosphere.
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For certain? Just outside the orbit of the space station.
Actually, we can say with some certainty there is no life on the Moon, which is farther than the space station (the likelihood of life on the dark side of the moon is incredibly low, almost non-existant).
Beyond that is anyone's guess, really.
[edit] Yes, I know there's no "dark side," but that's what we call the side that is faced away from Earth. I was saying that since there's an incredibly strong likelihood that there's no life on the side we can explore, it's reasonable to say there's probably no life on the side we *can't." Also, since the "dark side" is blasted with debris and rocks constantly, the natural reaction for life would be to move to the side we can explore since it's safer, in which case if we were to see life we would've seen it already.
Actually, on later visits, didn't NASA find that bacteria on various equipment from the moon landings had survived for years? I wonder if it's still alive up there ...
We more than likely took mold spores to the moon that are just sitting there....waiting.
It is hypothesized by some (not proven) that maybe Deinococcus radiodurans could. But the bacteria would be inert/inactive even if it was there.
Read that as Deionychus at first. Was a bit confused as to how we unknowingly blasted dinosaurs up to the moon.
Yes, but there's some question if this was due to later contamination of the samples. See here.
....you know there's not actually a "dark side of the moon", right?
Pretty sure he meant the side that we do not see. Also, in a literal sense, there is a dark side of the moon. It would be the half that is not pointed towards the sun at any given moment.
I'm pretty sure it's called that because radio communications with Earth are impossible there.
As a matter of a fact it's all dark
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The face of the moon we see does shift slightly as it goes through its orbit. It kind of rocks back an forth as seen in this image.
A hundred million album sales says different.
What about Venus/Mercury/Sun? Can we say for certain there's no life there?
edit: venus is closer
Actually at it's closest point, venus is a bit closer. Pioneer and Mariner didn't see anything that seemed "lifelike" and 92 bar pressure and 800 degree temps make it "Highly unlikely."
The right question is not "life" but rather "life as we know it." Gotta leave the window open for rock-monsters.
that there is no life on the surface of the moon. We can't say with 100% accuracy (which I consider "certainty") that there is no life on the moon,
What about the space between?
And about the wicked lies we tell?
That's just the surface of the moon, though. If some of Thomas Gold's ideas on the topic turn out to be true, there might be underground bacteria. I wouldn't bet on it, but we're talking about certainty here. He had a habit of invading a new field every so often, making a bold claim and being spectacularly right or spectacularly wrong with approximately equal frequency.
Fungi also live underground! One cubic inch of soil can contain more than 8 miles worth of mycelium! Why don't they ever consider this!?
Forgive my likely ignorance, but could you please elaborate on
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actually, the 'dark side of the moon' is not a dark side at all. it goes through the same 24 hour day cycle that the earth goes through. however, it's rotation, relative to the sun, has established that there is a hemisphere that we cannot see from the earth. until we put something on the far side, and specifically put something on the ground , and sample EVERYWHERE, there is no way that we could absosmurfly say that there is not life there. it's just not very likely, lol. a minimal atmosphere such as the moon's is highly unlikely to support life
edit: forgot an important 'not'
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I wouldn't quibble with you on that, but we don't know that there is no life on the moon with certainty. That was my only point.
With as much certainty as we could reasonably have from the data we've collected. Nothing we've found has ever given us a reason to believe there we would be life on the moon.
I absolutely agree. I was never trying to imply anything to the contrary.
You mean to tell me that Apollo 18 wasn't a documentary?!?! Dammit!!!,
Every area of the moon, barring some craters at the poles, receive the same amount of light through each month.
Minor nit-pick; there is no "dark side of the moon," there's just the side of the moon that faces away from us. It still gets light.
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I think everyone missed this, unless you arent being totally literal
Yes, I was being literal. We don't know for certain that there is no life on the moon.
By that same logic, we don't know anything for certain. You might be experiencing a simulation right now. I think it's a pity that the thread gets derailed by this sort of quibbling, instead of by useful responses.
And your's is a useful response? I think not. And, as to my answer, I believe that it is the only factual answer possible. If you don't like it, come up with a better one instead of going full pompous ass on me.
I don't know for certain that there isn't an invisible dragon in my garage. Science isn't at all about certainty, it's about varying levels of likelihood: