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A.DIM
2013-Sep-10, 04:36 PM
An expanded way of organizing our ignorance is discussed HERE (http://www.astrobio.net/interview/5660/the-drake-equation-revisited-an-interview-with-sara-seager).

Instead of aliens with radio technology, Seager has revised the Drake equation to focus on simply the presence of any alien life. Her equation can be used to estimate how many planets with detectable signs of life might be discovered in the coming years.
...
Not all of the terms in the equation can be calculated. The last two are just guesses. For the fraction of planets that have life, I put in one. I wanted to be optimistic. It really matters what you speculate for this term. You can put your own number in.

Detectable signatures of gas could mean a lot of things. As human beings, we exhale carbon dioxide. That’s our biosignature gas. But that's not useful because carbon dioxide in the atmosphere is naturally occurring. There are other possible gases we could look for. Oxygen is produced by plants and photosynthetic bacteria. We have also considered ammonia as a biosignature gas.

I carefully crafted the last term of this equation so one could actually add more information in. Does life produce a detectable signature? Are there systematic effects that rule out some biosignature gases being detected in some planets? Can we not find the signature for technical reasons? We just don't know how many planets have life that is producing biosignature gases that are detectable by us.



Neat!

Selfsim
2013-Sep-11, 10:54 AM
I cannot see any difference between the issues discussed ad nauseum with the Drake Equation, and this one.

What's the news here?

The punchline here is that if we're really lucky and everything works in our favor, we will be able to infer signs of life on those planets. We have a shot—I'd call it a remote shot—of finding life within the next decade.
Exactly how does 'infer signs', suddenly get morphed into a claim of 'finding life', (and that's irregardless of whether she thinks it might be a 'remote shot', or not)?

Sorry .. the content of this article is amongst the poorest, (in scientific research terms), I've seen for quite a while.
Its almost not worth publishing (IMO)!

JustAFriend
2013-Sep-11, 09:59 PM
Biggest problem is that you can get results that infer life but may only be exotic chemistry or conditions we just don't understand.

We had a hard enough time with that on the early Mars probes and that planet is right next door to us.

John Mendenhall
2013-Sep-12, 12:52 AM
Biggest problem is that you can get results that infer life but may only be exotic chemistry or conditions we just don't understand.

We had a hard enough time with that on the early Mars probes and that planet is right next door to us.

Agreed. Seeing chemistry that can be produced by life does not mean that it is produced by life.

A.DIM
2013-Sep-12, 01:43 AM
Agreed. Seeing chemistry that can be produced by life does not mean that it is produced by life.

Agreed.
My only hangup is choosing "exotic" chemistry over what we observe, and know.
Take Levin's experiment aboard Vikings for example. It met the premission criteria for detecting biological activity yet no other life detection package has been considered since. A preference was taken and the evidence ignored. This, in my opinion, is a major scientific blunder: not following the evidence. And what have we learned about Mars since? As I see it, plenty to support Levin's position.
As far as Sara Seager's revisionist work, I guess we'll have to wait until Webb and TESS results. I suspect they won't disappoint.

iquestor
2013-Sep-22, 04:47 PM
I can't participate in a thread like this without referencing Garik Isrealian's TED Talk "Detecting Alien Life with Spectroscopy (http://www.ted.com/talks/garik_israelian_what_s_inside_a_star.html)". If you havent seen it, take 12 minutes and watch it, its very, very informative.

His arguments:

1. There can be no life as we know it without geothermal processes: Tectonics and Volcanism.
2. Radium, Thorium and Potassium are the primary power sources for these processes.
3. Detection of these elements establishes that life processes are possible, then further investigation ensues.
4. further, from analyzing earthshine we get spectral lines indicative the large areas of vegetation itself, and not just detection of CHON, Methane, etc.
So vegetation in large areas on an exoplanet would result in unique spectral lines*
5. finally, detection of "miraculous" signatures of chemicals or molecules in an atmosphere of an exoplanet points to artificial generation, ie technology.

his conclusion is that in 15 years we can possibly find an exoplanet with enough evidence that we can say there is life there.

* I assume that he is making the assumption that said vegetation uses some type of photosynthetic process to convery starlight ot energy as the vegetation does on Earth.
If so then I think he is probably correct this would show up as spectral lines and , based on what we know of the relationship between Sol's light spectrum and the spectral lines generated by earth vegetation, possibly we could see if the same relationship exists when corrected for differences.

Colin Robinson
2013-Sep-22, 10:49 PM
I can't participate in a thread like this without referencing Garik Isrealian's TED Talk "Detecting Alien Life with Spectroscopy (http://www.ted.com/talks/garik_israelian_what_s_inside_a_star.html)". If you havent seen it, take 12 minutes and watch it, its very, very informative.

His arguments:

1. There can be no life as we know it without geothermal processes: Tectonics and Volcanism.
2. Radium, Thorium and Potassium are the primary power sources for these processes.
3. Detection of these elements establishes that life processes are possible, then further investigation ensues.
4. further, from analyzing earthshine we get spectral lines indicative the large areas of vegetation itself, and not just detection of CHON, Methane, etc.
So vegetation in large areas on an exoplanet would result in unique spectral lines*
5. finally, detection of "miraculous" signatures of chemicals or molecules in an atmosphere of an exoplanet points to artificial generation, ie technology.

his conclusion is that in 15 years we can possibly find an exoplanet with enough evidence that we can say there is life there.

* I assume that he is making the assumption that said vegetation uses some type of photosynthetic process to convery starlight ot energy as the vegetation does on Earth.
If so then I think he is probably correct this would show up as spectral lines and , based on what we know of the relationship between Sol's light spectrum and the spectral lines generated by earth vegetation, possibly we could see if the same relationship exists when corrected for differences.

I've just listened to the talk. The advances in spectrography are impressive, but I'm not convinced spectrography by itself would be able to demonstrate life beyond Earth.

For instance, vegetation might be detectable IF it was chemically very similar to Earth vegetation -- not just similar in the sense of being made of CHON, but similar in the sense of containing starches and chlorophyl... but how likely is that?

It is easy to talk about "life as we know it", but one of the basic things we know about life is that it evolves, and that evolution involves random mutation. Organisms on another planet may have evolved ways of doing photosynthesis, but will they be the same as the ways used on Earth? If they do photosynthesis a somewhat different way, will spectrography be able to distinguish between an unfamiliar living chemistry and an unfamiliar non-living chemistry?

I still think strong evidence of life beyond Earth is more likely to be found within our own solar system, where it will be possible to look at the morphology of organisms (e.g. using microscopes) as well as at their chemistry.

iquestor
2013-Sep-22, 10:58 PM
I've just listened to the talk. The advances in spectrography are impressive, but I'm not convinced spectrography by itself would be able to demonstrate life beyond Earth.

For instance, vegetation might be detectable IF it was chemically very similar to Earth vegetation -- not just similar in the sense of being made of CHON, but similar in the sense of containing starches and chlorophyl... but how likely is that?

It is easy to talk about "life as we know it", but one of the basic things we know about life is that it evolves, and that evolution involves random mutation. Organisms on another planet may do photosynthesis, but will they do it the same way? If they do it a somewhat different way, will spectrography be able to distinguish between an unfamiliar living chemistry and an unfamiliar non-living chemistry?

I still think strong evidence of life beyond Earth is more likely to be found within our own solar system, where it will be possible to look at the morphology of organisms (e.g. using microscopes) as well as at their chemistry.

Good Post. I've been browsing through "How to find a habitable planet" by James Kasting. He has written alot about what finding CHON, especially 02 and O3 would mean in an atmosphere. He says in the book that finding them in a planetary atmosphere would get him to about 99% certainty that life processes are present. Also he writes, its possible to determine palentary oceans, not just water vapor using a polarization technique, however not possible with any planned missions.

Selfsim
2013-Sep-23, 12:04 AM
Ok .. I've seen this presentation before.

The purpose of the presentation is to provide SETI searchers with information about what might be of interest to science. The hypothesis: "Carbon based exo-life may exist", is a valid scientific hypothesis. It is testable and verifiable. Isrealian's presentation provides particular spectrographic models, which would help to constrain known uncertainties in the interpretation of these specific observations, should they occur.

The discussion then shifts to the likelihood, (or otherwise), of these observations actually being made. In this sense, the discussion is no different from whether: "ETIs are 'more likely' to exist, or not", which, (as we hopefully) know, relies on philosophical beliefs and logical techniques, as distinct from the empirical scientific process.

Isrealian's pre-specified spectrographic signature models, are also not a sufficient basis for concluding that the remote diagnosis of ETI life's existence, by using this technique, is necessarily practically feasible in terms of returning reliable information (to sufficient resolution), which is capable of eliminating other uncertainties inherent in remote exo-planetary measurements at spatial (light-year) distances.

Spectropolarimetry models which allow for a conclusion of the existence of terrestrial life, are themselves, subject to key assumptions (http://cosmoquest.org/forum/showthread.php?141031-Detecting-Distant-Life&p=2096148&highlight=spectropolarimetry#post2096148) in the spectropolarimetry model itself, which can be said to only apply for local observations of Earth's life case instance. (See the papers in the link). The measurements are subject to highly variable characteristics of things like cloud cover and other weather patterns, which introduce huge uncertainties in the radiative transfer models, as well as in any given set of remote observations involving light reflective ground-cover.

Again, find some spectra of interest from 'out there', and we can discuss the uncertainties of the measurement at that time.

Colin Robinson
2013-Sep-23, 12:48 AM
Good Post. I've been browsing through "How to find a habitable planet" by James Kasting. He has written alot about what finding CHON, especially 02 and O3 would mean in an atmosphere. He says in the book that finding them in a planetary atmosphere would get him to about 99% certainty that life processes are present. Also he writes, its possible to determine palentary oceans, not just water vapor using a polarization technique, however not possible with any planned missions.

A New Scientist article (http://www.newscientist.com/article/dn23193-huge-telescopes-could-spy-alien-oxygen.html#.Uj-JnOCUDJw) that says atmospheric oxygen would be a "tantalising hint of life".

If spectrography identified substantial amounts of O2 and O3 in the atmosphere of a planet with other Earth-like features, presence of life might be considered the most plausible explanation. Even so, it wouldn't give the same certainty as close-up observation of an actual specimen, which missions within our own solar system may be able to provide.

iquestor
2013-Sep-23, 12:58 AM
Ok .. I've seen this presentation before.

The purpose of the presentation is to provide SETI searchers with information about what might be of interest to science. The hypothesis: "Carbon based exo-life may exist", is a valid scientific hypothesis. It is testable and verifiable. Isrealian's presentation provides particular spectrographic models, which would help to constrain known uncertainties in the interpretation of these specific observations, should they occur.

The discussion then shifts to the likelihood, (or otherwise), of these observations actually being made. In this sense, the discussion is no different from whether: "ETIs are 'more likely' to exist, or not", which, (as we hopefully) know, relies on philosophical beliefs and logical techniques, as distinct from the empirical scientific process.

Isrealian's pre-specified spectrographic signature models, are also not a sufficient basis for concluding that the remote diagnosis of ETI life's existence, by using this technique, is necessarily practically feasible in terms of returning reliable information (to sufficient resolution), which is capable of eliminating other uncertainties inherent in remote exo-planetary measurements at spatial (light-year) distances.

Spectropolarimetry models which allow for a conclusion of the existence of terrestrial life, are themselves, subject to key assumptions (http://cosmoquest.org/forum/showthread.php?141031-Detecting-Distant-Life&p=2096148&highlight=spectropolarimetry#post2096148) in the spectropolarimetry model itself, which can be said to only apply for local observations of Earth's life case instance. (See the papers in the link). The measurements are subject to highly variable characteristics of things like cloud cover and other weather patterns, which introduce huge uncertainties in the radiative transfer models, as well as in any given set of remote observations involving light reflective ground-cover.

Again, find some spectra of interest from 'out there', and we can discuss the uncertainties of the measurement at that time.

We would of course need to find a planetary atmosphere which gives us signatures discussed in order to evaluate them and make extraordinary claims.

The argument is not that observations (showing positive signs of life) are more or less likely to occur; I take his statements as assuming if LAWKI biospheres are out there, we could find one in the next 15 years or so due to the work that is in progress. I think he is optimistic that they are there, and they will be found. Of course, that is an opinion. Based on what I have read, current spectroscopic equipment isnt able to make some of the measurements required to define all of the elements we would be looking for.

"How to find a habitable planet" does a pretty thorough job of discussing how these spectra may appear, and what we can or cannot deduce from them. A lot of its over my head. Some of the methods that might give a positive result arent technologically possible in the next 30 or so years, though.

Selfsim
2013-Sep-23, 04:42 AM
We would of course need to find a planetary atmosphere which gives us signatures discussed in order to evaluate them and make extraordinary claims.

The argument is not that observations (showing positive signs of life) are more or less likely to occur; I take his statements as assuming if LAWKI biospheres are out there, we could find one in the next 15 years or so due to the work that is in progress. I think he is optimistic that they are there, and they will be found. Of course, that is an opinion. Based on what I have read, current spectroscopic equipment isnt able to make some of the measurements required to define all of the elements we would be looking for.I don't think its just a matter of whether a LAWKI biosphere is out there, either. The orientation of an "exo-world" relative to its host star, relative to the Earth's position during the measurement period, plays a huge role. Not all "exo-worlds" will have the right orientation for observation. Noticing an exo-planet's atmospheric reflection or absorption spectra along the limb of a distant and relatively dim and tiny exo-planet, is no straightforward matter. (Interpreting it accurately, is another matter again). (Exo-moons might be even worse). At some point, there is a tradeoff between what the technology is capable of detecting, and the nature of an object's observable physical properties. This tradeoff is somewhat of a moving target itself. There are no 'slam-dunks' that allow anyone to accurately claim that detection of certain targets will be a certainty in the future. They may always be beyond reach, even if advances in observation technology sensitivity continues to develop at the present pace. How all that impacts detection of an ETI, is anyone's guess.

Predicting that such an exo-planet might be found in a given distant timeframe is, at best, pure guesswork .. and that's regardless of spectroscopy's proven reliability when it comes to verifying new instances of the various sub-atomic phenomena which cause characteristic absorption (or emission) spectra.


"How to find a habitable planet" does a pretty thorough job of discussing how these spectra may appear, and what we can or cannot deduce from them. A lot of its over my head. Some of the methods that might give a positive result arent technologically possible in the next 30 or so years, though.There is no assurance about anything being technologically possible, in any distant future period of time (unless one believes the distant future is already determined that is .. and that is no assurance at all).

Paul Wally
2013-Sep-23, 03:20 PM
For instance, vegetation might be detectable IF it was chemically very similar to Earth vegetation -- not just similar in the sense of being made of CHON, but similar in the sense of containing starches and chlorophyl... but how likely is that?



I wonder whether such photosynthetic vegetation really does have to be chemically similar to Earth's in order to leave the same general kind of signature or 'relationship', as iquestor puts it.



If so then I think he is probably correct this would show up as spectral lines and , based on what we know of the relationship between Sol's light spectrum and the spectral lines generated by earth vegetation, possibly we could see if the same relationship exists when corrected for differences.

I think this is an interesting notion. Perhaps there is such a general relationship between the spectrum of a star and whatever photosynthetic planet orbits such a star. Such a relationship would then be a consequence of evolution, independent of what the detailed chemistry might be.

iquestor
2013-Sep-23, 04:36 PM
I wonder whether such photosynthetic vegetation really does have to be chemically similar to Earth's in order to leave the same general kind of signature or 'relationship', as iquestor puts it.



I think this is an interesting notion. Perhaps there is such a general relationship between the spectrum of a star and whatever photosynthetic planet orbits such a star. Such a relationship would then be a consequence of evolution, independent of what the detailed chemistry might be.

Maybe. The book I have been referencing ( "How to build a habitable planet") talks a lot about the so called red-edge of chlorphyll detection on the spectral lines of earthshine. They first tried looking for it in earthshine from the moon (after subtracting the lines controbuted by moonlight) and then from data gathered by Galileo Probe as it passed Earrh and headed out for Jupiter.

The book acknowledges that we "knew what to look for" during these experiments, because we know Earths current atmosphere and details on chlorphyll, etc. Also looking at how blue-green algea and vegetation on Earth use photosynthesis, there certainly could be other methods and processes used by alien vegetation to convert starlight to energy, however it cites research that indicates that earth vegetation does it the best way, energy efficiency-wise. Since taking the path of least resistance is a common theme in natural and chemical processes, perhaps alien vegetation will ave similar enough photosynthetic processes that we can detect them using this method.

Further I would speculate that vegetation covering a planets surface does so to take advantage of sunlight in order to use it for energy, so some sort of spectral line would show up; however if the process it uses is very different we probably couldnt explain it until we knew directly about the vegetation...

Colin Robinson
2013-Sep-23, 08:43 PM
Maybe. The book I have been referencing ( "How to build a habitable planet") talks a lot about the so called red-edge of chlorphyll detection on the spectral lines of earthshine. They first tried looking for it in earthshine from the moon (after subtracting the lines controbuted by moonlight) and then from data gathered by Galileo Probe as it passed Earrh and headed out for Jupiter.

The book acknowledges that we "knew what to look for" during these experiments, because we know Earths current atmosphere and details on chlorphyll, etc. Also looking at how blue-green algea and vegetation on Earth use photosynthesis, there certainly could be other methods and processes used by alien vegetation to convert starlight to energy, however it cites research that indicates that earth vegetation does it the best way, energy efficiency-wise. Since taking the path of least resistance is a common theme in natural and chemical processes, perhaps alien vegetation will ave similar enough photosynthetic processes that we can detect them using this method.

Further I would speculate that vegetation covering a planets surface does so to take advantage of sunlight in order to use it for energy, so some sort of spectral line would show up; however if the process it uses is very different we probably couldnt explain it until we knew directly about the vegetation...

Perhaps spectroscopy would tell us enough to show that the atmosphere is far from chemical equilibrium, and that there are large organic molecules of unknown composition — the sort of things which we know already about Titan...

Selfsim
2013-Sep-23, 10:13 PM
… I think this is an interesting notion. Perhaps there is such a general relationship between the spectrum of a star and whatever photosynthetic planet orbits such a star. Such a relationship would then be a consequence of evolution, independent of what the detailed chemistry might be.Such a relationship would be subject to chaotic atmospheric (and other) effects, when observed remotely.

Selfsim
2013-Sep-23, 10:18 PM
Perhaps spectroscopy would tell us enough to show that the atmosphere is far from chemical equilibrium, and that there are large organic molecules of unknown composition — the sort of things which we know already about Titan...We'd need to consider just which part of the atmosphere is being observed, too. There are different effects, at different column depths .. how could one resolve what's happening at ground-level from remote observations at light-year distances, in order to make a conclusion of thermodynamic disequilibrium (for eg)?

iquestor
2013-Sep-23, 11:51 PM
We'd need to consider just which part of the atmosphere is being observed, too. There are different effects, at different column depths .. how could one resolve what's happening at ground-level from remote observations at light-year distances, in order to make a conclusion of thermodynamic disequilibrium (for eg)?

perhaps with several observations (which would take many years) some kind of averaging might give a better overall indication? If its earthlike enough as far as weather goes I would assume land masses, oceans clouds and other variables would cause the readings to differ.

The detection of vegetation in earthshine was greatly reduced when the light was diffracted over large areas of the Atlantic which is colder, with less blue-green algea and vegetation. Higher when the pacific with its warmer waters was prominant.

The book also asserts that the holy grail detection of O2/O3 + methane or O2 + N20 would be considered an almost overwhelming indication of LAWKI; the presence of O2 or N2O reduces the potential of methane to be produced abiotically. They were able to detect these from the Galileo data, proving its possible, IF you can get enough quality photons. Thats the extremely hard part.


Perhaps spectroscopy would tell us enough to show that the atmosphere is far from chemical equilibrium, and that there are large organic molecules of unknown composition — the sort of things which we know already about Titan...

being out of equilibrium is one of the tattletales they feel might indicate life processes at work

Paul Wally
2013-Sep-24, 12:23 AM
We'd need to consider just which part of the atmosphere is being observed, too. There are different effects, at different column depths .. how could one resolve what's happening at ground-level from remote observations at light-year distances, in order to make a conclusion of thermodynamic disequilibrium (for eg)?

I don't think the resolutions are high enough yet to observe any part of a remote planet. The spectroscopic data would be of light coming from the planet as a whole. But does it require 3-D spatial resolution to infer chemical disequilibrium? I would think that data on general chemical composition would be sufficient for at least a probabilistic conclusion.

Selfsim
2013-Sep-24, 09:05 AM
I don't think the resolutions are high enough yet to observe any part of a remote planet. The spectroscopic data would be of light coming from the planet as a whole. But does it require 3-D spatial resolution to infer chemical disequilibrium? I would think that data on general chemical composition would be sufficient for at least a probabilistic conclusion.The light comes from the planet's host star when the planet occults. The ultimate technique, (for ultimately applying to exo-planets/moons), I think, might be the same as what they did back in 2001 when Titan occulted a background binary stellar pair, (except obviously, Titan is a lot closer than distant exo-planets). By observing the changes in the light levels when viewed from the ground-based Palomar Hale telescope, they figured out all kinds of things (about Titan), like wind velocities at different altitudes in the different hemispheres, atmospheric temperature and density profiles, and the average atmospheric opacity. Paper here (http://ao.jpl.nasa.gov/Palm3K/Publications/Scientific/bouchez_adaptive_optics_2003.pdf). ('Twas reported 7 years later (http://www.universetoday.com/72273/watch-titan-occult-a-binary-star-system/), by UT, on December 2010 :rolleyes: ).

Now, I agree that resolutions are a long way from being able to do detect some of these things for an exo-planet at light-year distances (this may not even be a realistic or achievable goal either), but the Titan exercise at least provides some broad guidelines for the kind of technology performance levels needed for this degree of detail, (ie: beyond just detecting an unchanging spectrum, that is). Atmospheric temperature for eg, I would think, would be an important measurement parameter for determining disequilibrium ..

I think trying to infer from spectropolarimetry models, and trying to capture surface vegetation reflections, might be (highly) wishful thinking.