Evidence for ET More Likely Biased

[Selfsim]

In contrast with the other monster thread: 'Evidence for ET is mounting daily, but not proven.', this article, (which has appeared previously in PhysOrg), seems to have resurfaced again just recently:

Expectation of extraterrestrial life built more on optimism than evidence, study finds.

But Princeton University researchers have found that the expectation that life — from bacteria to sentient beings — has or will develop on other planets as on Earth might be based more on optimism than scientific evidence.
… {snip}...
While these observations tend to stoke the expectation of finding Earth-like life, they do not actually provide evidence that it does or does not exist, Spiegel explained. Instead, these planets have our knowledge of life on Earth projected onto them, he said.
…{snip}...
Yet, when what is known about life on Earth is taken away, there is no accurate sense of how probable abiogenesis is on any given planet, Spiegel said. It was this "prior ignorance," or lack of expectations, that he and Turner wanted to account for in their analysis, he said.

{My snips and underlines}

The study, (by Turner and Spiegel), uses Bayesian analysis techniques to minimise prior scientific assumptions, in order to end up with a more objective view for shaping our expectations on the question of exo-life.

Such techniques seem beneficial in managing frequently undistinguished, overly optimistic, (and pessimistic), expectations of exo-life.

This study shows that the relationships we project onto Kepler exo-planetary discoveries, in so far as it concerns the possibility of exo-life amongst Earth-like planets, are more likely to be driven by optimistic human expectations, rather than scientific "evidence". (Hence is "Evidence for ET", really mounting ??)

Regards

[eburacum45]

The paper can be read here
http://arxiv.org/abs/1107.3835

Although a 'best guess' of the probability of abiogenesis suggests that life should be common in the Galaxy if early-Earth-like conditions are, still, the data are consistent (under plausible priors) with life being extremely rare, as shown in Figure 3. Thus, a Bayesian enthusiast of extraterrestrial life should be significantly encouraged by the rapid appearance of life on the early Earth but cannot be highly confident on that basis.

[Paul Wally]

"Our analysis suggests that abiogenesis could be a rather rapid and probable process for other worlds, but it also cannot rule out at high confidence that abiogenesis is a rare, improbable event," Spiegel said. "We really have no idea, even to within orders of magnitude, how probable abiogenesis is, and we show that no evidence exists to substantially change that."

The problem is really to understand the phenomenon of abiogenesis. Once we can explain how abiogenesis happens it becomes then possible to derive useful probabilities. Since we have no probabilities we can neither say that expectations are over-pessimistic nor over-optimistic. In the absence of sufficient evidence to work out probabilities a possibly useful heuristic is to simply look for the kinds of things we do know and understand.

[mutleyeng]

so far, i cant find anything in this thread to disagree with.
The only thing that i find curious is why it required a research paper to come to that conclusion.
There is nothing wrong with the exploration of our wider enviroment being driven by optimistic human expectations... thats kinda the spirit of exploration in a nutshell.
I think a breakthrough in the understanding of Abiogenesis is the most realistic avenue for arriving at meaningful assesments of life in the universe that is available to us.
But I still want to know about all them lovely exo planets regardless.

[centsworth_II]

What we really need is a space telescope powerful enough to do spectroscopy on the atmospheres of earth-like planets. Although this is far off it may actually occur before the cracking of the abiogenesis mystery. Studying the atmospheres of prebiotic planets could help our understanding of how abiogenesis occurred on Earth. Then there's the possibility of discovering potential post biotic atmospheres.

[Selfsim]

What we really need is a space telescope powerful enough to do spectroscopy on the atmospheres of earth-like planets.

Although this is far off it may actually occur before the cracking of the abiogenesis mystery.

The capability presently exists ..

A recently released (Nov 2011) paper claims confirmed detection of a strong 3.3 micron feature, (corresponding to the methane v3 branch), in the atmosphere of HD 189733b (a hot Jupiter ~63 Lyrs distant). (Done by the Spex spectrograph at the NASA Infrared Telescope Facility, atop Mauna Kea). There are several other of these projects presently underway, or under consideration including space-based 'scopes.

Studying the atmospheres of prebiotic planets could help our understanding of how abiogenesis occurred on Earth. Then there's the possibility of discovering potential post biotic atmospheres.

How would one actually know whether the planet/moon under study was pre- or post-biotic ?

Regards

[centsworth_II]

How would one actually know whether the planet/moon under study was pre- or post-biotic?

Of course, one wouldn't know. Hopefully a catalog of earth-like planet atmospheres could be built up to the point where there could be a categorization of atmosphere types. Maybe even the evolution of earth-like atmospheres could be determined by examining the atmospheres of earth-like exoplanets of various ages. After a great deal of such information has been compiled there may become evident a certain population of atmospheres with distinguishing characteristics that could be hypothesized as resulting from the presence of life.

All that is a long way off.

[Selfsim]

Of course, one wouldn't know. Hopefully a catalog of earth-like planet atmospheres could be built up to the point where there could be a categorization of atmosphere types. Maybe even the evolution of earth-like atmospheres could be determined by examining the atmospheres of earth-like exoplanets of various ages. After a great deal of such information has been compiled there may become evident a certain population of atmospheres with distinguishing characteristics that could be hypothesized as resulting from the presence of life.

All that is a long way off.

Well, why wait till then ?
It seems the criteria for developing an exo-biology/exo-atmosphere inference hypothesis is so loose, just about anyone can come up with anything they like, and then go from there assuming the existence of exo-life. Actually, it seems that the belief in exo-life comes first, and everything else which follows, then becomes 'evidence for' that belief.

So, no need to wait !

Regards

[iquestor]

I think we will be able to say within a decade or two that life very probably exists on this or that exoplanet based on spectroscopic results and a lot of circumstantial evidence. Right now if we found a rocky earth-sized planet orbiting about a star similar to our sun in size and age within a range conducive to having liquid water, and we were to determing CHON from the atmosphere, as well as water vapor, and signs of photsynthetic processes, then we could reasonably say there is likely life there which is similar to earth life. This would not be conclusive, but very, very compelling.

I am optimistic that we may find a planet candidate or two along these lines. based on what Kepler seems to be finding, earth sized planets arent uncommon. I think we will have in excess of 70 target planets to begins searching within a couple of years. If earthlike life starts wherever the conditions are right, at least a few of these should show some signs of life. If we have this many candidates, and none show signs of life, then either life there isnt earthlike, or it isnt there at all. Either way these results are compelling.

[Selfsim]

I think we will be able to say within a decade or two that life very probably exists on this or that exoplanet based on spectroscopic results and a lot of circumstantial evidence. Right now if we found a rocky earth-sized planet orbiting about a star similar to our sun in size and age within a range conducive to having liquid water, and we were to determing CHON from the atmosphere, as well as water vapor, and signs of photsynthetic processes, then we could reasonably say there is likely life there which is similar to earth life. This would not be conclusive, but very, very compelling.

Feelings of compulsions aside, the results as you say, would be inconclusive.

I am optimistic that we may find a planet candidate or two along these lines. based on what Kepler seems to be finding, earth sized planets arent uncommon. I think we will have in excess of 70 target planets to begins searching within a couple of years. If earthlike life starts wherever the conditions are right, at least a few of these should show some signs of life. If we have this many candidates, and none show signs of life, then either life there isnt earthlike, or it isnt there at all. Either way these results are compelling.

Once again, feelings of optimism and compulsion aside, if 'life signs' aren't detected, it may be for any number of other reasons ... ie: for example, life testing isn't feasible over light-year distances, or we don't have sufficient 'target planets' or .... {insert: any number of a myriad of unknown reasons}

[eburacum45]

To prove the existence of life elsewhere we will probably have to send a probe there and examine it in detail (unless we can communicate with it in other ways). Even if we have what looks like a near-certain telescopic identification of life there remains the possibility that some abiotic process could mimic the same results.

Conversely there might be worlds that appear lifeless from a distance but in fact support a biosphere; these undetectable life-bearing worlds might be in the majority.

A third option is that some worlds might support phenomena which resemble life in some ways, but not in others; I call this category 'life-like processes'. A planet with self-replicating and evolving molecules with no cell walls, perhaps, or self-replicating but non-evolving robots left behind by a long vanished race. Where are the boundaries between pre-biotic and biotic, and between natural and artificial? I doubt we will be able to find out without going there, and possibly not even then.

[Selfsim]

To prove the existence of life elsewhere we will probably have to send a probe there and examine it in detail (unless we can communicate with it in other ways). Even if we have what looks like a near-certain telescopic identification of life there remains the possibility that some abiotic process could mimic the same results.

Conversely there might be worlds that appear lifeless from a distance but in fact support a biosphere; these undetectable life-bearing worlds might be in the majority.

A third option is that some worlds might support phenomena which resemble life in some ways, but not in others; I call this category 'life-like processes'. A planet with self-replicating and evolving molecules with no cell walls, perhaps, or self-replicating but non-evolving robots left behind by a long vanished race. Where are the boundaries between pre-biotic and biotic, and between natural and artificial? I doubt we will be able to find out without going there, and possibly not even then.

I agree.
My simple point all along has just been that it is just not feasible to send a probe light-years in order to conduct the direct 'life-test' experiment, locally.

It is also not feasible to transmit results obtained, (even if the test was somehow feasible), back to Earth if the same distances are involved. The power requirements outstrip our technologies, or the physical devices required to increase a return message signal gain, would be far too bulky to be transported. Even sample return over such distances isn't feasible. The string of communications 'repeater' stations idea ... along the line of sight, would also not be feasible from a fuel requirements/orientation precision perspective, also.

We're just dreaming if we think any of these problems are surmoutable.

The best chance would be if in some future Kepler mission, the spacecraft was re-oriented and it detected an Earth-like exoplanet under light years distant. Even then it would be a huge stretch .. but I would concede that such a scenario might at least be practically feasible.

But man, we're talking about a lot of good luck with that one, methinks !

Regards

[A.DIM]

In contrast with the other monster thread: 'Evidence for ET is mounting daily, but not proven.', this article, (which has appeared previously in PhysOrg), seems to have resurfaced again just recently:

Expectation of extraterrestrial life built more on optimism than evidence, study finds.

But of course! How many missions to Mars, or elsewhere, have been designed specifically to look for life? And how many have been sent to merely investigate "habitability?" If that's all mission planners can get approved then optimism, coupled with circumstantial evidence, is what one is left with.

This part, however, made me think: In fact, the researchers conclude, the current knowledge about life on other planets suggests that it's very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low.
"Fossil evidence suggests that life began very early in Earth's history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn't reveal much about the actual probability of life on other planets," Turner said.

"Life took shape unusually fast" only if you cram its origin into an earth-sized time frame. If one considers Genome increase as a clock for origin and evolution of life it would seem life could be dated to ~10G years ago.

Regards

[Selfsim]

Hi A.Dim;

But of course! How many missions to Mars, or elsewhere, have been designed specifically to look for life? And how many have been sent to merely investigate "habitability?" If that's all mission planners can get approved then optimism, coupled with circumstantial evidence, is what one is left with.

Well, I think this is getting closer to the truth of the matter. I find it rather refreshing to be discussing authentic issues, over rather poorly constructed smoke-screens.

This part, however, made me think: In fact, the researchers conclude, the current knowledge about life on other planets suggests that it's very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low.
"Fossil evidence suggests that life began very early in Earth's history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn't reveal much about the actual probability of life on other planets," Turner said.

"Life took shape unusually fast" only if you cram its origin into an earth-sized time frame. If one considers Genome increase as a clock for origin and evolution of life it would seem life could be dated to ~10G years ago.

The matter of extrapolating from Earth's fossil records in order to estimate the possible distribution of hypothesised exo-life, is mathematically invalid unless one is of the view (opinion) that Earth is not modelled fairly as an isolated system - in which case, one would expect life to be found in an HZ fairly nearby - like Mars, eh ?

The information systems understanding of the evolution of the human genome invariably involves chaotic processes … which results in unpredictability at certain scales, and predictability at others. The question then becomes one of the scale at which one is able to make second instance predictions reliable - if at all.

This paper fits a logarithmic regression curve of functional non-redundant genome size vs time of origin in major groups of organisms, in order to extrapolate backwards to come up with the 10 Gy origin estimate. The fit is somewhat synthesised as they estimate genome size based on regression of this model from modern day genome sizes/complexity, (rather than direct fossil genome measurements). The graph in Figure #1 combines prokaryotes and eukaryotes, but the two had very different evolutionary trends. As mentioned, I don't believe evidence exists for how big the genome size was for early prokaryotes, so I doubt the model's credibility when it comes to real-life evidence bases. (The idea however, is only at the early hypothetical stages, so it is probably unfair to judge it on this basis alone).

Its certainly an interesting perspective though .. one well worthy of a few reads, IMHO .. and one to file on the shelf and occasionally review, as the thinking matures.

My overall feeling however, (for what its worth), is that imposing a power law relationship on some sketchy inference data, and specifically excluding the 'non-coding' parts of organism genomes, assumes a level of understanding of genetics, which I don't believe has yet been achieved in microbiological research areas.

Regards

[A.DIM]

Hi Selfsim!

The matter of extrapolating from Earth's fossil records in order to estimate the possible distribution of hypothesised exo-life, is mathematically invalid unless one is of the view (opinion) that Earth is not modelled fairly as an isolated system - in which case, one would expect life to be found in an HZ fairly nearby - like Mars, eh ?

Certainly, and I’m near certain in my opinion life will be found on Mars (if it wasn’t already). But what evidence, I wonder, is called upon to show Earth is modeled “fairly” as an isolated, or closed, system? Is there really evidence for this?
Whatever the case, I think it’s mathematically invalid to extrapolate much, if anything, from an example of one.

The information systems understanding of the evolution of the human genome invariably involves chaotic processes … which results in unpredictability at certain scales, and predictability at others. The question then becomes one of the scale at which one is able to make second instance predictions reliable - if at all.

Agreed; we’re only now beginning to acknowledge how much a hand in evolutionary advance HGT (horizontal gene transfer) has had; a seemingly chaotic process.

This paper fits a logarithmic regression curve of functional non-redundant genome size vs time of origin in major groups of organisms, in order to extrapolate backwards to come up with the 10 Gy origin estimate. The fit is somewhat synthesised as they estimate genome size based on regression of this model from modern day genome sizes/complexity, (rather than direct fossil genome measurements). The graph in Figure #1 combines prokaryotes and eukaryotes, but the two had very different evolutionary trends. As mentioned, I don't believe evidence exists for how big the genome size was for early prokaryotes, so I doubt the model's credibility when it comes to real-life evidence bases. (The idea however, is only at the early hypothetical stages, so it is probably unfair to judge it on this basis alone).

The author touches on this in the “author’s replies”:
I have addressed this problem in discussion by estimating the average rate of increase in genome complexity in Archaea and Eubacteria which appear lower than the rate of complexity increase in eukaryotes. Then I discuss 2 possible scenarios: (a) initial rates of complexity increase in prokaryotes were similar to those observed in eukaryotes and then slowed down due to organization constraints, or (b) rates of complexity increase in prokaryotes were always slower than in eukaryotes. With scenario (a), the expected origin of life is ca. 10 billion years ago according to regression (Fig. 1), and with scenario (b), life originated even earlier than that. Thus, separate handling of prokaryotes and eukaryotes does not bring the predicted date of life origin closer to present.
For all we know, the characteristic complexity of the prokaryotic genomes had been reached very early on during life's evolution (considering the geochemical and paleontological evidence of more or less modern-like microbiota ~3.5 billion years ago) and remained in equilibrium ever since. Thus, to the best of our understanding, there was an early explosive phase of evolution of complexity, which was followed by stasis (the prokaryotic phase of life's history) and then by another burst associated with eukaryogenesis.

Its certainly an interesting perspective though .. one well worthy of a few reads, IMHO .. and one to file on the shelf and occasionally review, as the thinking matures.

Agreed, and this paper: ”Darwinian evolution in the light of genomics” discusses more what we know and what we might discover; I think it's a good companion piece.

My overall feeling however, (for what its worth), is that imposing a power law relationship on some sketchy inference data, and specifically excluding the 'non-coding' parts of organism genomes, assumes a level of understanding of genetics, which I don't believe has yet been achieved in microbiological research areas.

Yes, I agree there’s much yet to be learned but I suspect (for what it’s worth) ideas like this are in the right direction.
Thanks for taking the time!
Regards

[Selfsim]

Hi Selfsim!

Certainly, and I’m near certain in my opinion life will be found on Mars (if it wasn’t already).

Good onya ... twill be intersting to see. I'm pretty sure it'll take more than MSL/Curiosity though !

But what evidence, I wonder, is called upon to show Earth is modeled “fairly” as an isolated, or closed, system? Is there really evidence for this?

Well, that's an interesting question ... I think we're speaking more specifically of the isolation of the biological buidling blocks (at a specific scale level), though. It would likely be falsified if we found an instance of Earth-related life on Mars, say .. (not put there by probe contamination, etc). Verification of the isolation of the biological building blocks at that same scale level would, (I think), require demonstration that such building blocks would not be viable outside the Earth habitat. (Which I suppose would be feasible, if the tolerances for viability were highly sensitive within the general region ... (ie: the Goldilocks thing)).

And here I've just heard this Chris McKay guy saying that we really don't know just how long 'dormant' life can remain viable. He points out that liquid water is only necessary for life processes ... but not for the 'dormant' phase, (ie: for species capable of achieving 'dormancy').

Agreed; we’re only now beginning to acknowledge how much a hand in evolutionary advance HGT (horizontal gene transfer) has had; a seemingly chaotic process.

Lots more to read and learn about this one ...

The author touches on this in the “author’s replies”:

Yep .. I read his response .. I'm not all that convinced, just yet.
The way he uses the term 'complexity' is a little tricky also. Information can be presented and measured as 'complex', but that doesn't necessarily map directly to the resulting organism being biologically 'complex' ...in his own words:

Biological complexity was recently defined by Adami et al.[8] as a size of functional and non-redundant genome.

.. which is the same definition he goes on to use.

Agreed, and this paper: ”Darwinian evolution in the light of genomics” discusses more what we know and what we might discover; I think it's a good companion piece.

.. Another very interesting read .. it'll take me a while to consume this one (and the other paper you posted on the other thread, also).

Yes, I agree there’s much yet to be learned but I suspect (for what it’s worth) ideas like this are in the right direction.

Sounds a little prescriptive for me ... however, the seeming specificity of the standard genetic code from amongst an astronomically proportioned possibility space, is the really big question. Durations greater than Earth's estimated age, would be a convenient explanation. (Pity convenience doesn't count in science, eh ?)

Thanks for taking the time!

Well, thank you for the interesting reference material ... much better to spend time consuming such material than arguing about opinions !
Regards

[nikkoo]

How would one actually know whether the planet/moon under study was pre- or post-biotic ?.