But finding oxygen and liquid water is not enough to conclude there is life on the planet.

No, but without oxygen and water, we can generally rule out advanced life as we know it, which is an advance in itself.

A large quantity of oxygen, which is unstable as an atmospheric gas, shows that something is producing it. Currently life is the most likely explanation for such an excess.

This would certainly be true, if we were looking for a preconceived notion of what life should look like. If we were looking for Carbon based organics that use oxygen/water, then the above statement would apply. If we were to open our minds and not make assumptions about what life can/can't do based on our limited experience with radically different life forms, then that statement would be false.

What sort of optics can see the two edges of a man's iris which is covered by eyelids?

I find it depressing that the National Academy of Sciences produced a 2010 decadal survey did not recommend and exoplanet discovery missions, possibly because all proposals were either deemed too expensive or too technologically risky. I know that exoplanet pioneer Geoff Marcy and others were strongly critical of the survey's choices.

If it can be ready for 2030, then this telescope should be the total priority, but only if it can be made big enough as to see habitable planets with enough resolution to detect live, from vegetation formations up to cities illuminated at night or big artificial infrastructures, as visible on earth from space. Then it would worth it to give it 80% of the Nasa budget for the next 15 years and even extra funds. But if all this at the end is just to see a point of light where you already know that there is a planet then forget about it.

This is awesome, and totally the kind of stuff NASA should focus on. Forget about manned mission. This is what matters for space exploration: telescopes and unmanned probes.

@Tangent2:

Are you talking about false positives or false negatives? If we find free oxygen then it is safe to conclude that there is life (the kinds we know about).

Failure to find free oxygen doesn't mean that there isn't life, just that if there is life it is a kind we are not very familiar with. There was life on earth before there was free oxygen in the atmosphere. . .

Geoff Marcy, planet hunter, unloads on the NAS's lack of extrasolar planetary observatory missions for the next 10 years...

http://blogs.natu..._fo.html

Puzzling given Kepler's pioneering success and discovery that planets abound including around the most prevalent red M stars. Then again, getting Kepler itself to fly was a decade long battle against established science in itself.

What would be truly revolutionary would be to find an infrared detector that would not need liquid helium to operate. Such a discovery would allow infrared telescopes (which detect exoplanets directly) to operate for more than three years before being decommissioned.

If it can be ready for 2030, then this telescope should be the total priority, but only if it can be made big enough as to see habitable planets with enough resolution to detect live, from vegetation formations up to cities illuminated at night or big artificial infrastructures, as visible on earth from space. Then it would worth it to give it 80% of the Nasa budget for the next 15 years and even extra funds. But if all this at the end is just to see a point of light where you already know that there is a planet then forget about it.

Even a spectrum from such a star, without the lights of cities and the green/black of vegetation, would allow for biosignatures/technosignatures to be detected with some orecision.

Just think, if those Vegans on 2012DA14 hadn't discovered how we are the hard way instead of having one of those telescopes to make them think twice about making this trip they wouldn't have wasted their time and have to turn back like they did to endure another lifetime and a half of being cooped up in that thing.

@Tangent2:

Are you talking about false positives or false negatives? If we find free oxygen then it is safe to conclude that there is life (the kinds we know about).

Failure to find free oxygen doesn't mean that there isn't life, just that if there is life it is a kind we are not very familiar with. There was life on earth before there was free oxygen in the atmosphere. . .

See my original post, it had the quote from the previous person that I was answering. That post contains the context of the statement and answers your question. You were basically reaffirming my assertion.

Good looking is looking good! =D An integrated coronagraph sounds much cheaper than having to launch a separate coronagraph.

@Tangent: It is impossible to untangle what you are asserting and then alluding to. Meanwhile nkalanaga's and LED's comments are certainly factual - seeing imbalances such as oxygen (or nitrogen oxides et cetera) on habitale planets (liquid water temperatures) is a test for life and life only.

@javkav: Direct imaging is a shortcut to uncover much more information on planets (size, habitability, et cetera) than earlier time consuming methods. It is therefore considered a priority in planet hunting circles.

seeing imbalances such as oxygen (or nitrogen oxides et cetera) on habitale planets (liquid water temperatures) is a test for life and life only.

I'm not sure that's such a clean cut case. NOx can also be created using nothing but methane and oxygen (and an energy source) - none of which necessitate life.
And there are also plenty of non-biological processes that can release oxygen.

No, but without oxygen and water, we can generally rule out advanced life as we know it

Which is sort of a problem: looking only for life 'as we know it' introduces already a tremendous bias. Certainly when trying to deduce from the data how prevalent life is out there.
(Then again: how would we look for life "as we don't know it"?)