Drake Equation: Estimating Life Supporting Planets & Detecting Life

[wolram]

http://en.wikipedia.org/wiki/Drake_equation

This equation is quite dated now, i wonder if it is still in the ball park, if not
what are present day estimates for possible life supporting planets?
And what about the detection of life forming chemicals, are they out there
in the right ratios, in the right places?

 

[Dr.Brain]

Drakes equation is vague. It is more of a logic rather than a real quantitative analysis.Anyways one of the thousands of SETI scientists had to do something.

BJ

 

[wolram]

Drakes equation is vague. It is more of a logic rather than a real quantitative analysis.Anyways one of the thousands of SETI scientists had to do something.

BJ

Agreed, but is there any better estimate, based on chemical evolution or
other observations?

 

[Dr.Brain]

Better estimates keep on getting worse.There are loads of things to be considered including the callowness of scientists.First we need to find stars around which we can expect the life-sustaining planets, then we need habitable-planets, then we need life to exist on them at the right time of planet-life, then we need to see if the life is intelligent and can communicate using good technology, then we need to consider : will that particular civilisation catch our signals? ... Or if they have the same or similar technology to decipher our signals.The chances of communication and replies from other intelligent civilisations are like 1 in a billion. We haven't been able to decipher something theoretically about extra-terrestial life, thinking of quantitative equations is certainly like commination to our knowledge.

BJ

 

[wolram]

Im not sure if Earth is unique, i doubt it with all that mass out there, but why
is it our planet has a, seemingly uncommon orbt, was there a special case for
the evolution of our slolar system?
If we could predict that special formation, if any, could we narrow our seach?

 

[Dr.Brain]

What type of uncommon orbit does our planet have? , Moreover we have seen the Earth as a planet with life but considering the fact that 1/100000000's of Earth's life has seen life on it , and all other years have been all without life, even a planet perfect as per its location for life will sustain life for only part of its life.Another Problem.

BJ

 

[wolram]

What type of uncommon orbit does our planet have? , Moreover we have seen the Earth as a planet with life but considering the fact that 1/100000000's of Earth's life has seen life on it , and all other years have been all without life, even a planet perfect as per its location for life will sustain life for only part of its life.Another Problem.

BJ

Well i am sure i am talking to the right person, someone who has knoledge of the
subject, may i suggest sir ,that you lead the way, maybe some insight as to our
finding a relative?

 

[turbo]

Moreover we have seen the Earth as a planet with life but considering the fact that 1/100000000's of Earth's life has seen life on it , and all other years have been all without life, even a planet perfect as per its location for life will sustain life for only part of its life.Another Problem.BJ

If you divide the 4.5Gy lifetime of the Earth by 100M as you suggest, we will get 45 years. Some of us are already considerably older than that. It is commonly accepted that life (as demonstrated by the microfossils) arose when the Earth was a billion years old or even younger, so the Earth has supported life for over 75% of it existence. If you believe that man as a sentient being is the only test of "life" and you believe that homo erectus emerged about 2 million years ago, then sentient life has been on Earth for 1/2250th of the Earth's existence. Life established itself here very early, though, and if our planet is not truly one-of-a-kind, there must be a lot of life out there.

 

[ohwilleke]

Drake's equation is a classic case of garbage in, garbage out. Until we have more data points it is impossible to get key parameters within even order of magnitude correct answers and the ultimate answer will be hopelessly corrupt.

 

[Andre]

You're not going to believe this but aliens not only exist, they also have caused global warming.

http://www.crichton-official.com/speeches/speeches_quote04.html on the effect of Drake on the scientific method is not very mild.

 

[Chronos]

Indeed, we cannot properly constrain all the Drake equation parameters. Crichton is, however, unduly pessimistic in saying
"...The problem, of course, is that none of the terms can be known, and most cannot even be estimated."
[thanks to Andre for that link] There is enough data to reasonably constrain all but a couple terms. In particular, up to and including the abundance of Earth like planets. While I suspect some form of life is highly likely to emerge on any very earthlike planet, that is purely speculative until there is at least one confirmed case - though even fossil evidence of life on Mars would, IMO, be compelling. Anyways, here are some of the plug ins to flesh out the Drake equation:

http://arxiv.org/abs/astro-ph/0306524
Title: What Fraction of Sun-like Stars have Planets?
The radial velocities of ~1800 nearby Sun-like stars are currently being monitored by eight high-sensitivity Doppler exoplanet surveys. Approximately 90 of these stars have been found to host exoplanets massive enough to be detectable. Thus at least ~5% of target stars possesses planets... [there is other evidence] suggesting that this estimate is still a lower limit to the true fraction of Sun-like stars with planets, which may be as large as ~100%.

http://arxiv.org/abs/astro-ph/0209383
Title: How common are Earths? How common are Jupiters?
A more difficult question to address is: How common are Earths? However, much indirect evidence suggests that wet rocky planets are common.

http://arxiv.org/abs/astro-ph/0103142
Title: Cosmological Constraints on Terrestrial Planet Formation
I attempt to piece together a consistent scenario based on current estimates of the evolution of the star formation rate of the Universe, the metallicity evolution of the star-forming regions of the Universe and the most recent observations of extrasolar planets. The precision of all of these data sets is improving rapidly, but they can already be combined to yield an estimate of the age distribution of earth-like planets in the Universe.

http://arxiv.org/abs/astro-ph/0012399
Title: An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect
The analysis done here indicates that three quarters of the earth-like planets in the Universe are older than the Earth and that their average age is 1.8 +/- 0.9 billion years older than the Earth. If life forms readily on earth-like planets - as suggested by the rapid appearance of life on Earth - this analysis gives us an age distribution for life on such planets and a rare clue about how we compare to other life which may inhabit the Universe.

And here is one example of how we might reasonably detect extrasolar life:
http://arxiv.org/abs/astro-ph/0503302
Title: Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants

 

[Dr.Brain]

If you divide the 4.5Gy lifetime of the Earth by 100M as you suggest, we will get 45 years. Some of us are already considerably older than that. It is commonly accepted that life (as demonstrated by the microfossils) arose when the Earth was a billion years old or even younger, so the Earth has supported life for over 75% of it existence. If you believe that man as a sentient being is the only test of "life" and you believe that homo erectus emerged about 2 million years ago, then sentient life has been on Earth for 1/2250th of the Earth's existence. Life established itself here very early, though, and if our planet is not truly one-of-a-kind, there must be a lot of life out there.

That was an estimate , you took it way too seriously.What I tried to point out is that , even planets perfect to sustain life will not experience life for most of the time they exist in the same form of lump.

Take Mars, life , might have existed there way back , we now see the planet as lifeless, even though it might have sustained life for the period Earth was in its lifeless stages.

BJ

 

[turbo]

That was an estimate , you took it way too seriously.What I tried to point out is that , even planets perfect to sustain life will not experience life for most of the time they exist in the same form of lump.

On the contrary, the Earth has supported life in some form for 3.5 billion years, which is more than 75% of its existence.

Take Mars, life , might have existed there way back , we now see the planet as lifeless, even though it might have sustained life for the period Earth was in its lifeless stages.

If Mars supported life a billion or two years ago, then life existed on two adjacent planets (Mars and Earth) at the same time.

 

[Dr.Brain]

Couldnt it have been possible that a 'billion or two' years ago Sun's radiational energy had more intensity as of now ? and Earth being closer to Sun didnot had conditions to sustain Life and Mars being a bit colder than Earth could sustain some life?

BJ

 

[Andre]

Indeed, we cannot properly constrain all the Drake equation parameters. Crichton is, however, unduly pessimistic in saying
"...The problem, of course, is that none of the terms can be known, and most cannot even be estimated."

Well, the question could be how much data you need of the unknown before it's scientically sound to abarrate into hypotheses. I see a number of reoccuring early -and obviously wrong- hypotheses that were very hard to abandon again, if at all. It would be better to wait judging until sufficient information is available. But this is against human nature.

For instance:

http://arxiv.org/abs/astro-ph/0209383
Title: How common are Earths? How common are Jupiters?
A more difficult question to address is: How common are Earths? However, much indirect evidence suggests that wet rocky planets are common.

How common are Venusses? If we were ever to increase the observing resolution to disthinguish the Earths from the Venusses, what would we find? 50-50? 99-1? 1-99? The latter is my guess. But should I guess or wait and see?

 

[wolram]

Thanks everyone

How many Earth like planets that exist is only part of finding life out there,
What about the mixtures of chemicals needed to make RNA, how would we
know if plant life is common but not human type life?

 

[Nereid]

Couldnt it have been possible that a 'billion or two' years ago Sun's radiational energy had more intensity as of now ? and Earth being closer to Sun didnot had conditions to sustain Life and Mars being a bit colder than Earth could sustain some life?

Yes, of course it could have been possible.

The problem with the kind of discussion we're (almost) having is, as ohwilleke pointed out early on, we have but a single datapoint. Actually, it's much worse than that ... we don't even have any null datapoints (e.g. there never was life on Venus; there never was life on the Moon; there is no life today on Jupiter; ...).

Chronos has given us a list of references to work which may be constraining some of the parameters, but (as ohwilleke also already said) the Drake equation is so tunnel-like that as to be almost garbage.

For example, the Earth, some 10 to 20 km down in hard rock, is a nice cosy place for several species of bacteria and archaea. Their cosy life has but the most tenuous connection to the Sun (and possibly none at all), as the source of their comfort is the rocks (food, energy) and the rocks (warmth). Do similar conditions exist, deep inside Ganymede? Titan? Triton? Could there be life in the crust of a 'rogue Earth', a rocky body adrift in interstellar space, free of the tyranny of a star?

{I could go on for several pages; I'd better stop here.}

 

[wolram]

By Neried

{I could go on for several pages; I'd better stop here.}

Well i for one am interested in the many possibilities, restrictions, for life on
other worlds, and i am sure you have a wealth of knowledged on the subject,
we all know most of this is guess work, so maybe a word or two more?

 

[Chronos]

...The problem with the kind of discussion we're (almost) having is, as ohwilleke pointed out early on, we have but a single datapoint.

There is no dissent on that point [unless SETI gets lucky]. But the fact there is no fewer than one example of life like us raises a not so trivial [IMO] question. The universe tends to let anything that can happen to happen as often as conditions permit. This leads to a question, which is not so easily answered. What feature [or combination thereof] of this particular planet is so rare there is a vanishingly small probabability of it having occurred elsewhere in the history of the universe? While we have not confirmed the existence of other Earth's like ours, we certainly not confirmed there is anything the least bit unusual about this particular solar system. Jupiters are quite common, and evidence continues to mount that smaller, more earthlike planets are equally prevalent. While the evidence is still pretty sparse, none of it to date suggests Earth's are exquisitely rare. If you are willing to concede that earth-like planets are not exquisitely rare, it's pretty tough to take the position that life is. And if life is relatively common, it smacks of anthropocentric conceit to think we are the cream of the crop.

 

[Nereid]

Up to here

And if life is relatively common, it smacks of anthropocentric conceit to think we are the cream of the crop.

I agree with you (except that, without any data worth its salt, we cannot put much confidence in 'earth-like planets may be common, so life too should be').

How life develops (evolves?) on an 'earthlike' planet with a history different from our own is purely speculative. Catling et al., in their recent paper, argue that an oxygen atmosphere is (very likely) essential for complex, carbon-based life to arise (interestingly, they define 'complex' to mean 'macroscopic animals'). We know that there were two 'bursts' of oxygen in the Earth's atmosphere, the first around 2.4 Ga, the second around 0.6 Ga. Only the second coincided with the appearance of animals. We have not a {insert your favourite expletive here} clue as to how such atmospheres can arise, whether they may take, on average 200 Gyears or 200 Myears (or whether their formation on Earth was astronomically rare). We know nothing about how life may evolve in the (long term) absence of an oxygen atmosphere, about the evolution of complexity in terms other than multicellularity, about the possibility of abundant oxygen in submarine 'water worlds' (such as Europa), ... {it's a very long list wolfram}

My particular favourite speculation is plants. Multicellular plants may well have existed since the first oxygen burst (the fossil record hasn't been examined all that closely), or even before. If multicellular animals never got started (for whatever reason), would 'intelligent plants' have evolved?

 

[turbo]

Is there any reason to suppose that prokaryotic organisms are less "alive" than more complex organisms? Certainly, the rate at which bacterial infections can kill us is an indication that these "primitive" forms of life are still kicking. The fact that eukaryotic life might have contributed to the "oxygen poisoning" of the prokaryotic organisms is illustrative of the success of plant life on earth. It may also be interesting to note that plants have been the source of many nice medicines that help control the simpler organisms that attack us vulnerable humans.

 

[Chronos]

Absolutely, Nereid. More observational evidence is required before any such hypothesis deserves any credibility. I'm betting on the not-so-rare Earth scenario because I find nothing to suggest earth-like planets are improbable. And given the appearance of life on Earth almost as soon as conditions permitted suggests life is highly probable under favorable conditions. Oxygen abundance is not much of an issue to me. Plants had plenty of time to oxygenate the atmosphere before critters arose and discovered they were delicious.

 

[Dr.Brain]

One more thing to be concerned about. Dont you think that finding planets is one thing, exoplanets.org claims that we have discovered like 150 so planets outside our solar system, but traveling to them is still a near impossible job .?... 15 light years is mammoth distance , we need to breed 20 generations inside a single spaceship ..

BJ

 

[wolram]

From NERIEDs link.
Since four billion years is almost half the anticipated life-time of our sun, life on other planets orbiting short-lived suns may not have had sufficient time to evolve into complex forms. This is because levels of oxygen will not have had time to develop sufficiently to support complex life, before the sun dies. Professor Catling said: "This is a major limiting factor for the evolution of life on otherwise potentially habitable planets."

So even if all the properties for life are abundant, there may not be time for the
evolution of inteligent beings, on some of these otherwise ideal planets.

 

[Nereid]

Since four billion years is almost half the anticipated life-time of our sun, life on other planets orbiting short-lived suns may not have had sufficient time to evolve into complex forms. This is because levels of oxygen will not have had time to develop sufficiently to support complex life, before the sun dies

(extract)
However, there is no a priori reason to accept the “Rare Earth” view of Ward and Brownlee (2000) that the oxygenation time on inhabited planets elsewhere will be about the same as the Earth’s or prohibitively longer so that habitable planets are generally baked by their parent star’s red giant phase before complex life gets the chance to arise. We could imagine that some planetary parameters elsewhere may be even more favorable than Earth’s for allowing the accumulation of atmospheric O2

IOW, read the paper, not the press release from the marketing department!

PS, I have read the paper, and have four pages of densely written notes and comments on it ... mostly critical.

 

[wolram]

This paper 30 pages suggests to me, that the road to intelligent life is by no
means straight forward, or without hazards.
http://lgmacweb.env.uea.ac.uk/esmg/papers/Chapter06-FINAL.pdf

It seems to me that finding ideal planets for life, is only the tip of the
ice berg