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ZunarJ5
2013-Jan-07, 09:23 PM
At the end of this article;

http://www.universetoday.com/99091/five-planets-around-nearby-star-tau-ceti-one-in-habitable-zone/

there is a quote, stating, “Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these planets in the not-too-distant future."

How much about a planets atmosphere is it expected we will be able to learn?

If a planet almost identical to Earth (completely hypothetical... I use Earth as an example because it is the only example of a life full world that we have) is in our neighborhood (10-20 LY?), could the richness of life be detected with this technology?

I understand that we can not do this yet, it does say "not-too-distant future"... but it implies that studying the atmosphere of distant worlds is far from impossible.

Finally, if the advancements mentioned are not expected to be able to detect signs of life, how likely is it that such a technology might be invented... and how far off might it be?

Thank you.

ASTRO BOY
2013-Jan-07, 09:34 PM
Yep, great stuff and another nice article from "Universe Today".

I would imagine if we did find a planet with a similar atmosphere containing Oxygen and water vapour, the first thing we would do is focus on trying to detect any radio transmissions for advanced lifeform.
Any primitive life might be undetectable....But I could be wrong.

Selfsim
2013-Jan-07, 09:58 PM
The best method, (that I'm aware of so far), suggested for attempting to do this, involves using spectropolarimetry and examining the polarisation signatures of reflected light. So far, we can only correlate Earth's polarised spectral signature with Earth-life.

We have no way of interpreting other polarised spectral signatures, should these come from exo-planets which may/may not harbour 'life'. We would have to confirm via some other means, that life exists there, (or somewhere other than Earth), in order to rule out other natural physical mechanisms, which might also explain the same light properties.

Its not so much a matter of being able to detect the light (although that is a challenge as well) … the issue is interpreting what caused a particular signature. At the moment we have a few signatures from 'the local neighbourhood'. From memory, the technique didn't gain sufficient momentum to get a technology 'push', (probably because it wasn't capable of ruling out other possible causes).

My comments about this, and some relevant papers, are here. (http://cosmoquest.org/forum/showthread.php/129036-Life-in-the-Universe-Reflected-by-the-Moon?p=1994139#post1994139)

PS: Sterzik's paper on Bio-signatures from spectropolarimetry is here (http://www.eso.org/public/archives/releases/sciencepapers/eso1210/eso1210.pdf) and Stams' is here (http://arxiv.org/pdf/0707.3905v1.pdf)

IsaacKuo
2013-Jan-07, 10:02 PM
First off--regardless of whether it can be used to find signs of life, studying the atmospheric composition of these planets is compelling from a scientific perspective anyway. Our own solar system has no examples of super-Earth or mini-Neptune planets. Whether we see nitrogen atmospheres or carbon dioxide atmospheres or hydrogen atmospheres or no atmospheres...they will all be fascinating data points which we currently utterly lack.

IsaacKuo
2013-Jan-07, 10:06 PM
We have no way of interpreting other polarised spectral signatures, should these come from exo-planets which may/may not harbour 'life'.
Umm...of course we have ways of interpreting other spectral signatures. We do it all the time with other planets and moons, as well as with stars and brown dwarfs. Interpretation of spectral signatures is a well understood and sophisticated scientific tool.

mutleyeng
2013-Jan-07, 10:33 PM
At the end of this article;

http://www.universetoday.com/99091/five-planets-around-nearby-star-tau-ceti-one-in-habitable-zone/

there is a quote, stating, “Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these planets in the not-too-distant future."

How much about a planets atmosphere is it expected we will be able to learn?

If a planet almost identical to Earth (completely hypothetical... I use Earth as an example because it is the only example of a life full world that we have) is in our neighborhood (10-20 LY?), could the richness of life be detected with this technology?

I understand that we can not do this yet, it does say "not-too-distant future"... but it implies that studying the atmosphere of distant worlds is far from impossible.

Finally, if the advancements mentioned are not expected to be able to detect signs of life, how likely is it that such a technology might be invented... and how far off might it be?

Thank you.

I bumped into a chap on google plus thats currently doing an astronomy phd focsing on exoplanet atmospheres. Hes got a pretty good website thats worth a look
http://www.paulanthonywilson.com/

Selfsim
2013-Jan-07, 10:50 PM
Umm...of course we have ways of interpreting other spectral signatures. We do it all the time with other planets and moons, as well as with stars and brown dwarfs. Interpretation of spectral signatures is a well understood and sophisticated scientific tool.Ok .. so lets get 'down and dirty' … (yet again) :) …

Say we find a 'confirmed' exo-planet, (ie: no longer a candidate), for which we can calculate its mass, surface temperature (ie: the calculable physical parameters, resulting in relatively small residual uncertainties). The atmospheric spectral signature shows the same compounds and elements as Earth .. but in different proportions.

Let's stretch it a bit further … say we've developed sufficient precision to detect a polarimetric signature, (maybe via the Webb?). Its resemblance to Earth's is also distinctly different (as best we can tell from those measurements).

(I hope this is agreed to be a 'plausible' scenario of equal probability to anything else classifiable within the 'Earth-like' exoplanet category, on the trail of bread-crumbs of perceived 'exo-life' ..??)

What data source do we then reference to make comparisons against, in order remove the remaining uncertainties, so as to enable a 'eureka' declaration of 'life'? Where is it? What does it contain? Where did it come from?

IsaacKuo
2013-Jan-08, 03:15 AM
Ok .. so lets get 'down and dirty' … (yet again) :) …
Look, you made an unscientific claim that we could only interpret spectral signatures which matched Earth's. This is scientific nonsense. Scientists can interpret the spectral data from all sorts of planetary bodies and stars.

Say we find a 'confirmed' exo-planet, (ie: no longer a candidate), for which we can calculate its mass, surface temperature (ie: the calculable physical parameters, resulting in relatively small residual uncertainties). The atmospheric spectral signature shows the same compounds and elements as Earth .. but in different proportions.
So what? We can make scientific interpretations based on the data, regardless of whether or not it matches Earth's.

In particular, the detection of any atmospheric components which should not be stable, or combination of components which should not be stable with each other, is suggestive of some interesting chemistry/geology/etc going on. In particular, the presence of atmospheric oxygen has, so far, been indicative of either photosynthetic life or ice sputtering or photodissociation. Also the presence of large amounts of methane in Titan's atmosphere is known to be a puzzle, and the origin is currently unclear. There are other molecules which would be certainly be artificial in nature, such as metallic aluminum, or detectable levels of fission reaction fallout.

Selfsim
2013-Jan-08, 03:57 AM
Look, you made an unscientific claim that we could only interpret spectral signatures which matched Earth's. This is scientific nonsense. Scientists can interpret the spectral data from all sorts of planetary bodies and stars.Did I say that?
A spectral 'signature' is more than a spectrum. There is virtually no question about certain peaks in a spectrum, being persistent characteristics of particular absorption or emission of certain elements or compounds.

A spectral 'bio-signature' however, requires a biological interpretive database (in order to recognise the 'signature' of the presence of en-masse biology). We only have one known signature relating to en-masse biology, and that comes from Earth's spectral 'signature(s)', as observed remotely, (from space).


So what? We can make scientific interpretations based on the data, regardless of whether or not it matches Earth's.

In particular, the detection of any atmospheric components which should not be stable, or combination of components which should not be stable with each other, is suggestive of some interesting chemistry/geology/etc going on. In particular, the presence of atmospheric oxygen has, so far, been indicative of either photosynthetic life or ice sputtering or photodissociation. Also the presence of large amounts of methane in Titan's atmosphere is known to be a puzzle, and the origin is currently unclear. Well if you acknowledge that the remote detection of methane in Titan's atmosphere has resulted in a 'puzzle', then this would be good evidence that remote spectroscopy alone, can still result in 'puzzles'.

Supported by that evidence, I'd then say that remote atmospheric detection of other so-called 'biogenic' gases might be subject to similar levels of uncertainty, given that we have so little experience of what other natural processes we don't yet know about ..


There are other molecules which would be certainly be artificial in nature, such as metallic aluminum, or detectable levels of fission reaction fallout.Sure … detection of certain very specific molecules might be more convincing than detection of known ubiquitous elements/compounds such as oxygen, methane or CO2.

I'd love to see these artificial substances turn up .. even I might get excited if these were detected .. (depending on the quantities of them, and the uncertainties inherent in the detection methods employed).

But what if they don't turn up?

IsaacKuo
2013-Jan-08, 03:04 PM
Did I say that? A spectral 'signature' is more than a spectrum. There is virtually no question about certain peaks in a spectrum, being persistent characteristics of particular absorption or emission of certain elements or compounds.
Those are spectral signatures. A spectral signature is any spectral features which are indicative of particular things.

A spectral 'bio-signature' however, requires a biological interpretive database (in order to recognise the 'signature' of the presence of en-masse biology). We only have one known signature relating to en-masse biology, and that comes from Earth's spectral 'signature(s)', as observed remotely, (from space).
Now you're just backtracking and moving goal posts around, and in fact you get the science wrong. None of the spectral signatures associated with Earth are "bio" signatures. They are all indicative of particular features, which in turn may or may not be deduced to be caused by various life forms.

So, for example, the existence of atmospheric oxygen is suggestive of a biological origin, but there plenty of other planetary bodies with atmospheric oxygen.

Well if you acknowledge that the remote detection of methane in Titan's atmosphere has resulted in a 'puzzle', then this would be good evidence that remote spectroscopy alone, can still result in 'puzzles'.
What you fail to realize is that this is a far cry from declaring that it is impossible to interpret the spectral signature. And what you fail to realize is that you are simply wrong about your claim that it's impossible to deduce the existence/nonexistence of life unless it's Earth-like.

You can try to cherry pick examples which fit your model, but this will never prove that all examples fit your model. Especially since I already gave examples which don't fit. Sorry, but that's how logic and science work.

Supported by that evidence, I'd then say that remote atmospheric detection of other so-called 'biogenic' gases might be subject to similar levels of uncertainty, given that we have so little experience of what other natural processes we don't yet know about ..

Sure … detection of certain very specific molecules might be more convincing than detection of known ubiquitous elements/compounds such as oxygen, methane or CO2.

I'd love to see these artificial substances turn up .. even I might get excited if these were detected .. (depending on the quantities of them, and the uncertainties inherent in the detection methods employed).

But what if they don't turn up?
If they don't turn up? Scientists do what they do anyway, interpret the spectral signatures they do detect to the best of their knowledge. That is what scientists do. You seem to think it's some great mysterious or scandalous or noteworthy thing that scientists don't know everything or can't figure out everything with certainty, but that's just how science is, most of the time, in the places where science is interesting!

My point still stands and your point is still wrong. If we find detectable levels of metallic aluminum or fission reaction fallout, those would be surefire proof of artificial origin. If we detect the spectral signature of satellites in synchronous orbit, those would be surefire proof of artificial origin. There are just some things which just don't happen naturally, and these would be proof of ET life regardless of whether or not this ET life were "Earth-like".

In order for your point to be correct, it would have to be true of every possible spectral signature, not just ones which you cherry pick.