An objective Bayesian analysis of life’s early start & late arrival

  • #1
jim mcnamara
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Summary:

Using Bayesian methods, authors find 9:1 odds in favor of the existence of extraterrestrial life

Main Question or Discussion Point

Article:
https://www.pnas.org/content/early/2020/05/12/1921655117
Phys.org link
https://phys.org/news/2020-05-odds-life-intelligence-emerging-planet.html

An issue I see is Mars and Venus. Mars may have had some life forms, and may still. Venus never got that far. So, in a sense, we are 1 for 3 in getting a planet to survive all the nastiness associated with being a planet in a solar system, in order to evolve some level of intelligent life. We would need vast numbers of rocky planets in the Goldilocks zone of middle aged stars (stars in the middle part of main sequence) to get past the all the disasters we have posited for Mars and Venus. And Earth, too: asteroid impacts that changed life on Earth without completely removing it. So far we have been able to detect at most a few Earthlike exoplanets close to stars. Most are smaller stars not like ours (G star) and are given to nasty outbursts, like CME's. And the Goldilocks Zone for them is close to all the fireworks.

So, is Earth a remarkable one off, or just part of a horde of life encrusted planets? Or because our sample of exoplanets needs a lot of improvement to establish they are out there, we are not sure.

Or I may misunderstand analysis.
 

Answers and Replies

  • #2
anorlunda
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Isaac Asimov wrote about non-carbon based life chemistries. That might broaden the range of Goldilocks zones.

Isaac Asimov "Not as We Know it – the Chemistry of Life". Cosmic Search. North American AstroPhysical Observatory (9 (Vol 3 No 1)).​

Asimov also wrote about chemistry that could make places like Titan candidates.
https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#cite_note-asimov-42 said:
Isaac Asimov, the biochemist and science fiction writer, suggested in 1981 that poly-lipids could form a substitute for proteins in a non-polar solvent such as methane. Lakes composed of a mixture of hydrocarbons, including methane and ethane, have been detected on the surface of Titan by the Cassini spacecraft.
But is your interest in intelligent life, or just life?
 
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  • #3
BillTre
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Many now consider the goldilocks zone to be overly limiting to where life might have arisen.
  • Large moons around large planets (like Jupiter and Saturn) can be warmed by gravitational tidal forces which in essence creates an additional goldilocks zone around some of these large planets.
  • Some have also postulated ice covered planets with interior areas kept warm by radioactive decay in their cores. These could in theory be flying around independent of a star.
 
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  • #4
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But is your interest in intelligent life, or just life?
... or just life like us?

I imagine somewhere in the universe with its trillion galaxies there are places inhabited by sentient gasbags or something that would consider Earth to be covered in a slightly interesting thin layer of motile carbon slime.
 
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  • #5
sophiecentaur
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Summary:: Using Bayesian methods, authors find 9:1 odds in favor of the existence of extraterrestrial life

So, is Earth a remarkable one off, or just part of a horde of life encrusted planets? Or because our sample of exoplanets needs a lot of improvement to establish they are out there, we are not sure.

Or I may misunderstand analysis.
I think that the state of our actual knowledge makes fanciful suggestions far too attractive. Just as soon as some form of extraterrestrial life is detected / recognised than the situation will change radically.
Until then we are just speculating and that could very easily take us into the realms of SciFi. To avoid disappointment, I think there are other far more fruitful channels for interest.
I'm not just being a grumpy old man but PF tries to keep things down to Earth for good reason.
 
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  • #7
sophiecentaur
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22% of sun like stars have a planet in the habitable zone. Should be around 11 billion of them in the Milky Way.
OK, so we can say that it is not impossible that we may find traces of extraterrestrial life. It's quite important to ask what we should do about this. How much of our resources should we expend on research. How important is this research (into a double negative, even), compared with dealing with climate change, poverty and the dreaded virus?
It could be said that the ship is sinking. Should we all be pumping or is it justified that someone is still painting the name on the stern?
Why is the topic of extraterrestrial life so appealing?
 
  • #8
sophiecentaur
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There's something else that may be of interest and that is the evidence of the time line of life on Earth. Fairly recent evidence indicates that eukaryotic life on earth only started up as recently as 1.5Byears. Life before that (billions of years worth of it) would have been bacterial and of much less interest to the public than possible little green men.
Any estimates about the likelihood of coming across 'really interesting' life forms is even less than popular opinion would like it to be.
 
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It could be said that the ship is sinking. Should we all be pumping or is it justified that someone is still painting the name on the stern?
Someone should be on the lookout for other ships.
 
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  • #10
sophiecentaur
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Haha. Hoist by my own analogy! 🧐
 
  • #11
sophiecentaur
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The presence of a nice chunky sized Moon and a tilted spin are factors to encourage an improved rate of evolution. Those factors should perhaps be included in the probability calculations too.
 
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  • #12
256bits
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The presence of a nice chunky sized Moon and a tilted spin are factors to encourage an improved rate of evolution. Those factors should perhaps be included in the probability calculations too.
Something along the lines of "necessary and sufficient " conditions.

1590738796402.png
 
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  • #13
sophiecentaur
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Something along the lines of "necessary and sufficient " conditions.
It's just adding more parameters into the Drake Equation. Personally, I resist getting too excited in anticipation of any 'treat' so I can always think of reasons why discovering life may be way in the future. Grumpy old devil, perhaps.
 
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