The silence is deafening....

As simpleisbetter said, the ancient Greeks not only knew the earth was a sphere, but also measured its size. Columbus' contemporaries knew this, and correctly criticized Columbus' proposal to sail west to India. More information here.

The SETI questions will likely not be answered for 100, 1,000 or more years. It is simply too early to make any suppositions one way or another.

I can realistically see somebody 1,000 years from now posting a similar comment on whatever form of social information networking is used at the time.

It is absolutely NOT too early.
We now perfectly know the appropriate conditions, chemical and physical, for Life to occur and many chemical reactions that were still mysterious in the 70's have been identified. No steps are particularly improbable. In short, a computer program fed with these priors could simulate the event for an exoplanet.
To go back to the example I used before, it's like we now know that if we take an acid in acqueous solution, therefore in water liquid, and mix it with a base in the same conditions, then a reaction MUST occur. Then do it, If nothing happen then reconsider the theory of acid/base.
Similarly, the biggest and best known requisite for life is WATER, liquid. That's not the only one but it's the most stringent filter in the 'simulation' mentioned above.
So, IF and When an exoplanet with liquid water is discovered, and no signs of life are detected, you'd better prepare the arguments to save the current theory of life.
One failure might be OK, but the theory won't survive two.

The problem, as someone mentioned earlyer, is that there is no rush to study the best candidate exoplanets known so far (which is not Kepler 22, according to this site:
http://phl.upr.edu/p...planets-catalog )
But maybe it's because none of these exoplanets are really THE best possible case scenarios, and nobody wants to invest an entire observation campaign in something with less than 100% of success.
Can you publish "Spectral study of Gliese 581g doesn't reveal any markers compatible with biological activity" ?
Some observatory seems to be capable, but maybe they want the glory without the risks?

"...The main facility at Paranal is the VLT, which consists of four near-identical 8.2-metre Unit Telescopes (UTs), each hosting two or three instruments. These large telescopes can also work together, in groups of two or three, to form a giant 'interferometer', the ESO Very Large Telescope Interferometer or VLTI, allowing astronomers to see details up to 25 times finer than those seen with the individual telescopes. The light beams are combined in the VLTI using a complex system of mirrors located in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres. With this kind of precision, the VLTI can achieve an angular resolution of milliarcseconds,..."
http://en.wikipedia.org/wiki/ESO

In short, a computer program fed with these priors could simulate the event for an exoplanet.

No, it couldn't. We can't even properly simulate the folding of a single protein molecule using only the 20 amino acids found in life on earth.

Just finding water is nowhere near enough to prove that a planet could support life. It is certainly one of the requirements for life like us, but definitely not sufficient. Salts and organic molecules are certainly required, as well as a reasonable pH range (I doubt we will find life in extreme acid or base, although it can certainly tolerate some departure from pH 7), but we don't have good criteria yet for exactly what ranges of salt, pH, etc. can produce life.

There is also the aspect of time. The earth did not start out with life - it took a billion years or so. How do we know that a water-bearing planet just isn't "ripe" yet? Some people have postulated that the moon started out much closer to the earth, causing mega-tides which eroded rock and resulted in the oceans becoming salty, which may have been a critical step for life. What if the planet doesn't have a suitably large and close moon for that process?

And most importantly, as several people have pointed out, we couldn't detect life on earth from the distance of Alpha Centauri right now. So until we get sufficient technology to detect a lot more detail about exoplanets than we can now, we can't say that there isn't life there.

Jarad

We now perfectly know the appropriate conditions, chemical and physical, for Life to occur and many chemical reactions that were still mysterious in the 70's have been identified. No steps are particularly improbable.

Not quite true. We know the conditions necessary for life to sustain itself. And that's a very broad range of conditions. What we don't know is all the conditions, steps, sequences, and events required for life to develop spontaneously from abiotic organic chemicals. And there's no indication that those steps allow for a broad range.

Water is certainly a necessary condition, but by no means sufficient. Protein chirality alone is a huge problem, and even though there are hints of progress on that one, it and many other issues are not yet resolved.

" We can't even properly simulate the folding of a single protein molecule using only the 20 amino acids found in life on earth.."

Jarad, not with a 100% certainty or accuracy, but models exist that can get you pretty close. Like for any simulation, total accuracy is impossible and some simplifications must be made, otherwise the model could take as long as the real thing to occur. Conditions that depends on the orbital parameters can be estimated by observation, again with more or less accuracy. The age of planetary system/dust rings have been mentioned too, i donno how they do it though.
But yes, the presence of the Moon seemed, if not critical, at least a very important event in Life's history. IMO, the big tides it created acted more like a catalyser which means that in abscence of a (big) moon, prebiotic chemistry would occuur but on a much longer time scale.

I am puzzled by your statement that we could not detect 'life' at about 4-5 light years. I think that several years observing a putative Earth orbiting a Sun at that distance with big mirrors in interferometry mode (milliseconds arc resolution as mentioned above), could yield some 'compatible markers', like Oxygen, some greenish hint in the spectra, maybe some specular reflection from the oceans directed to us.
That would not be definitve proof but that would encourage to build the only tool that can bring the final verdict:
Space Interferometer with very long base, nulling and all the hoopla.

Ilanitedave, yes, we don't know all the details. I could evade the problem like evolutionarist do: 'with enough time...'.
How can we reproduce in laboratory reactions that, when combined, start to look like prebiotic chemistry only after a million years?

No you can't evade it with time. We aren't talking about biological evolution, we're talking about the origin of life. They are two different sets of processes, with two different dynamics. That's one of the biggest reasons people mislead themselves on this topic, by conflating the two.

There's no known necessary requirement for long time periods for the origin of life. It might be required, it might not. We don't know. As for the combining of laboratory reactions, that's the other problem. We don't know what laboratory reactions to apply, regardless of the amount of time involved. We know some of the basic steps, but the details of those steps we do know, and other entire steps that are just as basic, are still not settled.

And that is coming from an optimist.

The idea you just articulated, Dave...it is as if it has been in my head for ages, but your clear articulation just made the issue...the n=1 issue so very clear to me. Though we understand some of the conditions under which evolution occurs, we cannot say we know the conditions under which the origin of life occurs.

Otto

Like for any simulation, total accuracy is impossible and some simplifications must be made, otherwise the model could take as long as the real thing to occur.

The real thing in terms of protein folding occurs in fractions of a second.

Conditions that depends on the orbital parameters can be estimated by observation, again with more or less accuracy.

Observation of what? If we had a set of planets with life and a set without, we could observe the orbital parameters and see if there are consistent differences. But with an N of 1, we can't.

I think that several years observing a putative Earth orbiting a Sun at that distance with big mirrors in interferometry mode (milliseconds arc resolution as mentioned above), could yield some 'compatible markers', like Oxygen, some greenish hint in the spectra, maybe some specular reflection from the oceans directed to us.

We don't have any scopes that could resolve any of those things right now.

And just seeing green won't mean anything - there are plenty of inorganic chemicals that can look green, and alien life won't necessarily use a green protein in their photosynthesis - they could evolve around a molecule that captures a different wavelength. Neither will seeing reflections - things other than water can be reflective.

More importantly, not seeing those things doesn't mean that life does not exist there. We can't even rule out life under the ice sheets of Europa, which is much closer. How could we rule out life on an exoplanet based on not seeing green from many lightyears away? What if their chlorophyll equivalent molecule is more efficient, and looks black (absorbing all visible wavelengths)?

Jarad

There is a gap in our understanding of the origin of life.

We can simulate in the lab early conditions with simple compounds, hit them with static discharges, and see the production of complex organic molecules that could be the precursors for life.

Once we have a self-replicating cell, we can drop it in that soup and watch it replicate and evolve.

But between the two there are at least 2 big steps that are not yet well understood: the generation of simple self-replicating molecules, and the leap to an enclosed system with a membrane to keep all the required parts together for self-replication.

There are lots of hypotheses about how these steps occurred (surface chemistry on clays, etc.), but these are all speculative. We don't know exactly how it happens or how long it "typically" takes.

As for declaring out current "theory of life" dead if we find 2 exoplanets without life, I would say that is false for 2 reasons:
1 - one or two examples isn't enough to disprove such a theory.
2 - we don't really have a developed theory to disprove.

Jarad

2 - we don't really have a developed theory to disprove.

And that's a biggie.

It may well be that there are a number of processes that can lead to life from nonlife. There may be only one. If we do succeed in doing it the lab, my first guess will be that we've stumbled on one of several.

This is one of those situations where it seems to me that theory is not primary to observation, probably something that Popper would have disputed. We're creating the theory as we do our experiments, one local hypothesis at a time.

Oooooo! I can finally add something scientific.....

You two wrote, "I think that several years observing a putative Earth orbiting a Sun at that distance with big mirrors in interferometry mode (milliseconds arc resolution as mentioned above), could yield some 'compatible markers', like Oxygen, some greenish hint....We don't have any scopes that could resolve any of those things right now. And just seeing green won't mean anything - there are plenty of inorganic chemicals that can look green..."


A half century ago...possibly before you two were born...necessity required me at age 15 to make my own telescope...the whole thing...grind/polish/cut/mount/cast iron weights...two years later, I ended up with an 8 inch F8 Newtonian with 1/2 wavefront error...maybe even a whole wave error...it was so bad when I got it back from Clausing who coated it for me, they put in a note disclaiming responsibility for all the sleeks. Seems one is suppose to clean the former grinding slurry away before going to the next finest grade. (would be a quarter century later when I stopped it down to an F11 6 inch that I discovered I could see the Cassini division)....

anyway, I digress....I turned this behemoth at Mars one summer, and I saw GREEN. I saw a definitie gray-greens. I can only think of three reasonable explanations:
1. a contrast effect of the darker areas against the reddish area
2. there's green cholorophyll on Mars
3. there were so many sleeks on the mirror, it was prismatic

Compared to me....you are mere theoreticians. I did real science!

Otto

There is not one theory, you are right, but many, BUT the thing is that they all converge toward a necessary autocatalytic molecular entity. Once this tipping point is reached, with autocatalytic molecular replicators trapped into oily vesicles, the transition from prebiotic to biotic is, i would say, not completely crazy.

Just following wikipedia links, you' ll see the hypothesis of a pre-RNA world: the PAH-World, (Polycyclic Aromatic Hydrocarbon, believed to be abundant on early earth, and even in the martian meteorit ALH, if i recall) that would promote the pre-RNA world through the steps explained in http://en.wikipedia....orld_hypothesis
A transient pre-RNA world would probably be short-lived, as it cannot compete well with the first really autocatalytic RNA forms.
http://en.wikipedia....orld_hypothesis
So now the RNA/TNA/GNA-replicators World trapped with amino-acids inside lipid vesicle is considered as the critical step, and I guess we can call this assembly THE 'protocell'. The emphasis is not anymore how do we get to this protocell but how do we get to the TNA/GNA/RNA replicator. In addition to the PAH, a pre-rna Lipid World has also been proposed.

Perhaps the ESA will some day revive the Darwin Array project. Using multiple satellites (to create a long baseline, essentially one big instrument in multiple parts) the ideas is to do spectographic analysis of "goldilocks zone" candidates around other stars. It would look for dynamic atmospheres with oxygen and water and trace elements that hypothetically require input from a biosphere to exist (ala Lovelock/Margulis etc).

" 2 - we don't really have a developed theory to disprove."

Hmm, yes, let's say we have a range of possibilities, instead. If the Moon is that much critical, for example, well, we might never find an earth-like exoplanet couple in our galaxy, so in this case I agree than NOT finding life in an exoplanet otherwise well situated in the goldilock zone would prove nothing.
But it's the WE, almost 6PM, clear skies, time to setup the scope. Clear sky guys.

Three hours, and no response by you mere theoreticians to my sage comments about doing actual science with exquisite astronomical equipment?

Just for that….I will now add a word of philosophy. (“A word” of philosophy, Otto? That’ll be the day!)

The ancient Greek language was more flexible than English. For example, its common verbs each had between two hundred and three hundred forms whereas in English our verbs have between fifty and a hundred forms. This flexibility allowed the speakers of Greek to articulate issues with fine and helpful degrees of nuance, conducive to displaying truth.

This degree of nuance can be seen in how the Greek language handled two topics we are addressing here, life and theory (life, as in "extra-terrestrial life" and theory, as in "you mere theoreticians"). In fact, the Greek language connects the two concepts of life and theory in an interesting way.

Greek has two words for life, bios (pronounced “bee-ohss”) and zoa (pronounced “zoh-ay”). Zoa was used to refer to the word life in the sense we have been discussing it here; i.e. living things. Bios was often used to refer to the type of life a person lived. The difference, then, between these uses of zoa and bios was similar to the distinction we have in English between “life” and “a life” as in the trite phrase, “get a life”. Bios was often attached to other words such as politikos as in bios politikos (the active/public life) and, relevant to our second topic, theoretikos as in bios theoretikos (the thinking/contemplative life).


But…I digress……


...we, you and I, stargazers and scopists all, we who consider looking through a telescope for hours on end getting bitten by mosquitoes, getting frost bite on our toes, and/or going without sleep, to be having just a fine time...the rest of the non stargazing world is pretty sure we, you and I, do not have, bioi (pronounced bee-oy; the plural of bios).

Oooooo! I can finally add something scientific.....

You two wrote, "I think that several years observing a putative Earth orbiting a Sun at that distance with big mirrors in interferometry mode (milliseconds arc resolution as mentioned above), could yield some 'compatible markers', like Oxygen, some greenish hint....We don't have any scopes that could resolve any of those things right now. And just seeing green won't mean anything - there are plenty of inorganic chemicals that can look green..."


A half century ago...possibly before you two were born...necessity required me at age 15 to make my own telescope...the whole thing...grind/polish/cut/mount/cast iron weights...two years later, I ended up with an 8 inch F8 Newtonian with 1/2 wavefront error...maybe even a whole wave error...it was so bad when I got it back from Clausing who coated it for me, they put in a note disclaiming responsibility for all the sleeks. Seems one is suppose to clean the former grinding slurry away before going to the next finest grade. (would be a quarter century later when I stopped it down to an F11 6 inch that I discovered I could see the Cassini division)....

anyway, I digress....I turned this behemoth at Mars one summer, and I saw GREEN. I saw a definitie gray-greens. I can only think of three reasonable explanations:
1. a contrast effect of the darker areas against the reddish area
2. there's green cholorophyll on Mars
3. there were so many sleeks on the mirror, it was prismatic

Compared to me....you are mere theoreticians. I did real science!

Otto

Dudley Leroy Clausing! Ah memories! Yes, clean up between grades of abrasive! Sam Brown!

-drl

Yes, yes....Sam Brown...and what was that nearly unreadable red 3 volume mirror grinding set called?

There is not one theory, you are right, but many, BUT the thing is that they all converge toward a necessary autocatalytic molecular entity. Once this tipping point is reached, with autocatalytic molecular replicators trapped into oily vesicles, the transition from prebiotic to biotic is, i would say, not completely crazy.

No, not crazy at all. Just not fully understood, so we don't know all of the requirements. Therefore we can't say that because we don't see it on one or two planets that it's wrong - those planets may just be missing one or more of the unknown requirements.

Jarad

There is not one theory, you are right, but many, BUT the thing is that they all converge toward a necessary autocatalytic molecular entity. Once this tipping point is reached, with autocatalytic molecular replicators trapped into oily vesicles, the transition from prebiotic to biotic is, i would say, not completely crazy.

Just following wikipedia links, you' ll see the hypothesis of a pre-RNA world: the PAH-World, (Polycyclic Aromatic Hydrocarbon, believed to be abundant on early earth, and even in the martian meteorit ALH, if i recall) that would promote the pre-RNA world through the steps explained in http://en.wikipedia....orld_hypothesis
A transient pre-RNA world would probably be short-lived, as it cannot compete well with the first really autocatalytic RNA forms.
http://en.wikipedia....orld_hypothesis
So now the RNA/TNA/GNA-replicators World trapped with amino-acids inside lipid vesicle is considered as the critical step, and I guess we can call this assembly THE 'protocell'. The emphasis is not anymore how do we get to this protocell but how do we get to the TNA/GNA/RNA replicator. In addition to the PAH, a pre-rna Lipid World has also been proposed.

I agree 100%. Protocells, or at least the vesicles that house them, are easy, you can make them in your kitchen. Turning them into self-sustaining replicators, well that hasn't been done by humans as far as I know. It's that "critical step" that is probably a combination of many steps, steps that may require clay, or calcite, or ice, or evaporation, or acids, or bases, or some combination of several. It may require that the products of a clay reaction interact with products of an ice + evaporation reaction, or some other intricate chains of circumstance to assemble just the right molecules in just the right sequences.

We simply don't know at this point. Of course it's not crazy, it happened at least once. The question is, and will be for the forseeable future, in what set of natural environments can it happen again? And how broad or narrow are the circumstances that allow it?

Doesn't the actual ocean and atmospheric chemistry itself depend on a complex chain of events, just as unlikely as life? That is, there's iron and nickel in the water, but there are microbes that use nickel and emit methane, which however declines because a type of iron oxide scrubs the water of nickel and the microbes die, so now oxygen can accumulate in the atmosphere etc. etc. etc. - it's extremely complicated and specific. Can these events happen in a different order leading to the same result?

-drl

Three hours, and no response by you mere theoreticians to my sage comments about doing actual science with exquisite astronomical equipment?

Just for that….I will now add a word of philosophy. (“A word” of philosophy, Otto? That’ll be the day!)

The ancient Greek language was more flexible than English. For example, its common verbs each had between two hundred and three hundred forms whereas in English our verbs have between fifty and a hundred forms. This flexibility allowed the speakers of Greek to articulate issues with fine and helpful degrees of nuance, conducive to displaying truth.

This degree of nuance can be seen in how the Greek language handled two topics we are addressing here, life and theory (life, as in "extra-terrestrial life" and theory, as in "you mere theoreticians"). In fact, the Greek language connects the two concepts of life and theory in an interesting way.

Greek has two words for life, bios (pronounced “bee-ohss”) and zoa (pronounced “zoh-ay”). Zoa was used to refer to the word life in the sense we have been discussing it here; i.e. living things. Bios was often used to refer to the type of life a person lived. The difference, then, between these uses of zoa and bios was similar to the distinction we have in English between “life” and “a life” as in the trite phrase, “get a life”. Bios was often attached to other words such as politikos as in bios politikos (the active/public life) and, relevant to our second topic, theoretikos as in bios theoretikos (the thinking/contemplative life).

That's interesting, actually, although knowing the history of our current word meanings doesn't do anything to change those current meanings. And yes, it does appear at first glance as if modern English doesn't support the nuances of meaning and categorizing that ancient Greek did. It might also be the case, however, that some of those old categories were artificial and superfluous? Or that the terms that are passed down to us via scholarly works of the ancients were perhaps their own versions of specialized jargon, and not used in the same way by lay contemporaries? Or more likely, that English is just as expressive, but simply using different lexical and grammatical methods?

I tend to think that all human languages are capable of rich expressions of narrative, poetry, and even technical description if skillfully and flexibly used.

But…I digress……

Hey, that's your second confessed digression in the same thread. I'll have to check to see if there's some sort of rule against that. (Or it may be a requirement, who knows?)

...we, you and I, stargazers and scopists all, we who consider looking through a telescope for hours on end getting bitten by mosquitoes, getting frost bite on our toes, and/or going without sleep, to be having just a fine time...the rest of the non stargazing world is pretty sure we, you and I, do not have, bioi (pronounced bee-oy; the plural of bios). \

Just goes to show you that simply because one may have the vocabulary doesn't mean they have the understanding. This zooid wouldn't trade his bios with any of 'em.

Doesn't the actual ocean and atmospheric chemistry itself depend on a complex chain of events, just as unlikely as life? That is, there's iron and nickel in the water, but there are microbes that use nickel and emit methane, which however declines because a type of iron oxide scrubs the water of nickel and the microbes die, so now oxygen can accumulate in the atmosphere etc. etc. etc. - it's extremely complicated and specific. Can these events happen in a different order leading to the same result?

-drl

The thing about that interaction is that it's mediated by life. So it's unlikely only in the sense that it could never happen in the absence of biological influence, and it may well be historical happenstance that the particular set of relationships came about at all. Now that they exist, though, they're sustained by feedback mechanisms. Whether them happening in a different order would have led to the same result, or a different but still self-sustaining result, is a worthy question for exploration.

It's an interesting thing that there are several possible forms that photosynthesis can take, which do not result in free oxygen as a byproduct. Had some non-oxygen-producing photosynthesizer become dominant early on, it's quite possible that an ecosystem similar to the one we know might never have become possible.

Almost everything about life can be thought of as contingent, accidental, and extremely unlikely taken on its own. But what's even more mindblowing to me is that the range of possibilities is so high that even if none of the unlikely events that led to us occurred, there would have been other, equally unimaginably improbable events that happened in the alternative, that would have led to far different communities than the ones we know, but nevertheless just as diverse and rich as our own. And they might consider themselves the most natural and inevitable result of life's development.

That was very good, Dave! Ouch! Touche! Oh my!

About us thinking freezing our **** off is a hot time...I've had a bunch of psychological tests done on me over the years of all sorts...I would enjoy getting a whole bunch of stargazers and scopists together....maybe the entire crowd at a starparty like NEAF or stellafane...and do a good old fashioned MMPI on all of them and see if there are common neuroses. I think that would be interesting.