Planets that could sustain alien life much rarer than thought

Discussion in 'Science, Tech, & Space Exploration' started by Spaceman spiff, Jun 12, 2019.

  1. Dejan Corovic

    Dejan Corovic Celestial

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    One of of modern scientific theories about life creation is called "rubbish bag" theory. There are these strange organic molecules, which look like cucumbers or like thick sticks. These 'cucumber' molecules have one end electrically positive and the other negative, so they tend to arrange themselves into larger cylindrical shapes that look like bags. They naturally occur in a shallow sea water with lots of sunlight, like little paddles of water on rocks along the shoreline. These bags capture inside, purely by chance, various organic molecules that are floating in these ponds on rocks. When calculated, probability of accidentally grabbing a bunch of organic amino acids that can form self-replicating chains, aka primitive DNA, is relatively high. Once amino acid chains start replicating, you've got the life.

    British-American scientist Stanton Freedman wrote an excellent book about it, that one can get on Amazon.
     
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  2. Shadowprophet

    Shadowprophet Truthiness

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    Is that a variation of panspermia? or something radically different? I don't think i've heard this one.
     
  3. CasualBystander

    CasualBystander Celestial

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    You need supervillians to get rid of 2 million feral cats. Normal people don't keep that huge a supply of poisoned sausages.

    Still amazed that marsupials don't eat poisoned sausage.
     
  4. CasualBystander

    CasualBystander Celestial

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    The "100 monkeys with 100 typewriters for 100 years could write Shakespeare" theory.

    Infinite monkey theorem - Wikipedia
    Also known as the infinite monkey theory.
     
    Last edited: Jun 14, 2019
  5. pigfarmer

    pigfarmer tall, thin, irritable

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    A friend lives near a feral colony and incomprehensibly attempts a catch & release neuter program. Crazy feel good nonsense. I say kill them. In his area you could literally whack a bunch every day while having coffee.

    But poisoned sausages .... I get it but it sounds weird. Beyond marsupials and feral cats there must be all sorts of other critters that’ll chow down
     
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  6. Dejan Corovic

    Dejan Corovic Celestial

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    Exactly, that's how whole natural world works.

    Here is the book if anybody wants to read it: Origin of Life. The "rubbish bag" is well known among biologists, but relatively unknown by public, although there are few videos on YT with info-graphics.
     
  7. CasualBystander

    CasualBystander Celestial

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    Dyson eh???

    I like his sphere and his vacuum, perhaps I should read his book.
     
  8. CasualBystander

    CasualBystander Celestial

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    A point that is frequently missed in the "6 million stars" argument is the Sun is an old generation 3 star.

    Stars that formed sooner wouldn't have enough heavy elements to support life as we know it.

    The Chemical Composition of Green Plants

    Things like:

    In addition to the carbon, hydrogen and oxygen that make up the vast majority of both plant and animal cells, plants will contain nitrogen, phosphorus, potassium, calcium, magnesium, zinc, sulfur, chlorine, boron, iron, copper, manganese and molybdenum. Some of these are found in only very trace amounts, and the composition may vary between different types of plants.


    Life formed around earlier generations of stars would have less of these elements.

    Given that the Sun is considered an old generation 3 star, we may be one of the first to have life.

    This also argues against life around the 88+ percent of stars that are red dwarfs.

    Red giants, or white dwarfs (another 5.5%) won't have life either.
     
    Last edited: Jun 16, 2019
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  9. pigfarmer

    pigfarmer tall, thin, irritable

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    Sometimes I think that intelligent life on this planet is just a persistent rumor
     
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  10. Dejan Corovic

    Dejan Corovic Celestial

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    There is much more to the evolution of life in the Milky Way and highly metallic stars. That article is too brief and too much focused on another subject.

    If you want to know more, here is a good source to find out more:

    The Age Distribution of Potential Intelligent Life in the Milky Way
    by Daniel Legassick, University of Exeter
    We investigated the habitability of the Milky Way, making use of recent observational analysis on the prevalence of Earth - sized planets, in order to estimate where and when potentially habitable star systems may have formed over the course of the Galaxy’s history. We were then able to estimate the age distribution of potential intelligent life in our Galaxy using our own evolution and the age of the Sun as a proxy. To do this we created a galactic chemical evolution model and applied the following habitability constraints to the Sun - like (G - type) stars formed in our model: an environment free from life - extinguishing supernovae, a high enough metallicity for Earth - sized planet formation and sufficient time for the evolution of complex life. We determined a galactic habitable zone as the region containing all the potentially habitable star systems in our model. Our galactic habitable zone contains stars formed between 11 and 3.8 billion years ago at radial distances of between 7 and 14 kiloparsecs. We found that most potentially habitable star systems are much older than the Sun and located farther from the galactic centre. By comparing the ages of these systems we estimated that ~77% of potentially habitable star systems are on
    average ~3.13 billion years older than the Sun . This suggests that any intelligent life in the Galaxy is likely to be incredibly more advanced th
    an we are assuming that they have evolved under similar timescales than we have. Implications and limitations of our study are discussed.
    https://arxiv.org/ftp/arxiv/papers/1509/1509.02832.pdf
     
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  11. CasualBystander

    CasualBystander Celestial

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    When running our simulations we found that the SNIa rate was approximately an order of magnitude higher than the SNII rate, when in fact observational data has shown that the SNIa rate is about an order of magnitude lower than the SNII rate

    When you read through the paper, they had some model problems that they used handwaving to overcome.

    Having look at this a bit more - the limitation seems to be nitrogen.

    Nitrogen is rare in the crust - about .000020 (20 PPM) or 0.002%.

    Carbon is about 1180 PPM.

    The nitrogen in the atmosphere is thought to come from a late cometary bombardment.

    Nitrogen in the sun is about 0.1%.

    Inside the orbit of Jupiter nitrogen isn't common (the asteroids are basically nitrogen free), since it is a volatile and gets cooked off. Venus has roughly the same amount of nitrogen as earth (3% of an atmosphere that is 93 bar).

    You need water, carbon, and nitrogen for amino acids.

    Your study estimated 1.4 million potential planets. It also mentions that 90% of them were sterilized at some point in their history.

    So we are talking about 140,000 planets.

    That is less than two orders of magnitude above my estimate.

    So I would accept it as a good starting point.

    Still don't understand why Venus has retained a 90+ bar atmosphere. The earth's original atmosphere is a matter of a lot of dispute but I tend to think it was at least 10 times as dense.
     
  12. Dejan Corovic

    Dejan Corovic Celestial

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    As I understand, vertebrae are only about 500 million years old, out of 4.5billion.

    If Earth was sterilized before vertebrae came to be, than it wouldn't matter too much. Microbes would be less affected by explosion of a nearby super-novae and life would spring back quickly. It's more likely that planets get hit by super-novae sterilization earlier in their lifespan, than later, because over the time number of super-novae is diminishing as more and more nebulae gas is converted into stars.

    Paper reported on limitations of their model, imposed to restriction of the allocated resources. But model benefited from increase in astronomical knowledge over last 40-50 years. That's why paper is providing very reasonable estimate.
     
  13. CasualBystander

    CasualBystander Celestial

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    It is interesting that all these studies say the best change for life is in the arms and don't predict much life in the core.
     
  14. Dejan Corovic

    Dejan Corovic Celestial

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    That is really reflecting in the number of species of alleged visitors. Estimates vary from 5 to 50. I am inclined to go for 5.

    But both 5 and 50 are extremely small numbers for a galaxy with 250 billion stars. For argument sake, if we accept that FTL is possible, and traveling between stars is regular thing, still traveling between galaxies would be definitely hard or almost impossible, because inter-galactic distances are millions of times bigger than inter-stellar.

    So it's safe to be inclined to say that both 5 and 50 species are coming from our galaxy.

    Maybe the reason they haven't killed us is because life in Milky Way is so rare, that aliens feel lonely.
     
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  15. Thomas R. Morrison

    Thomas R. Morrison Administrator

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    "Based on a statistical analysis of all the Kepler observations, astronomers at UC Berkeley and University of Hawaii, Manoa now estimate that one in five stars like the sun have planets about the size of Earth and a surface temperature conducive to life.

    Given that about 20 percent of stars are sun-like, the researchers say, that amounts to several tens of billions of potentially habitable, Earth-size planets in the Milky Way Galaxy."
    Astronomers answer key question: How common are habitable planets?
     
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  16. CasualBystander

    CasualBystander Celestial

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    3.5% of stars are G-type stars.

    Stars closer to the galactic center get scrubbed periodically.

    The F type and K type stars you are lumping in with the Sun would have either gone nova by now or have inferior (redshifted light).

    The sun's peak energy is in the yellow band. Photosynthesis only harvests down to about 720 nm.

    A K type star (20% solar output) would have to have planets much closer and the chance of a solar flare "scrubbing" would be much higher. There may be life but at a temperature that matches earth there would be less available food.

    If your theory was right - the various planet surveys would have turned up dozens of earths from the 4000+ they have spotted. In fact we can do the math: 20% * 4000 * 1/5 = 160. So one of them should be more or less an exact duplicate.

    Please enlighten me with the best "earthlike" planet from the survey.
     
  17. CasualBystander

    CasualBystander Celestial

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    Anyway - your 140,000 planets assuming 8 trillion light year volume would be one inhabited star per 57000 ly3 of volume.

    So the nearest inhabited star is about 46 ly away.

    Your paper's claim of 1.4 million planets (including the scrubbed one) says an earthlike planet should be 22 ly away and we should have already found it.

    They have detected gas giants up to 13000 ly away.... They have discovered rocky (or believed to be rocky) planets up to 226 ly away. So they should have found another earth by now.

    According to your paper within 226 ly they should have discovered 8482 habitable planets.

    The reason I am skeptical, is that given the distances they are finding planets, these claims of "earthlike planets" should be turning up in dozens or hundreds of near duplicates and they just aren't.

    But I'll grant that the techniques are getting better and this might change.
     
    Last edited: Jun 16, 2019
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  18. Thomas R. Morrison

    Thomas R. Morrison Administrator

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    False. We've been over this. Earth-sized worlds orbiting Sun-like stars in the habitable zone are nearly impossible to detect with our current technology: the only way we have a chance of detecting them is if their orbital ecliptic is perfectly aligned with the Earth so we can see them transit in front of their parent stars.

    That's why your argument is a failure of logic: given the limits of our detection capabilities only a rigorous statistical analysis can provide a reasonable understanding of the prevalence of Earth-like worlds in the habitable zones of their parent stars.

    But the Kepler Mission is having some success detecting Earth-sized planets that orbit very close to their parent stars:

    "Bottom line: With another 18 Earth-sized exoplanets found hiding in Kepler data, astronomers continue to confirm that not only does this kind of rocky world exist elsewhere, but also that they are rather common. How many of them may turn out to be habitable for some kind of life is still unknown, but these discoveries are bringing us closer to finding the first evidence for life outside of our solar system."
    Astronomers find 18 more Earth-sized exoplanets in Kepler data | EarthSky.org
     
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  19. Dejan Corovic

    Dejan Corovic Celestial

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    As far as wishful thinking goes, we want life to be rarer, rather than ubiquitous. If there was only 10 advanced hight-tech civilizations in Milky Way, that would be plenty. More life there is, around us, more wars and destruction there would be and more chance there would be for us to be blown up by aliens.

    If @CasualBystander 's most pessimistic projections are right, there still should be a small number, say bellow 100, of advanced civilisations in Milky Way.
     
  20. CasualBystander

    CasualBystander Celestial

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    Well...

    Morrison is good at defending the conventional scientific view. He is right that planet detection is difficult.

    But they are getting much better at it. They have detected a 1.9 earth radius planet at 226 LY.

    But the numbers he quotes are easy to test:
    6 million habitable planets (his number) means that there should be a habitable planet within 13.6 LY of earth.

    Out to 42 LY they have discovered about 30 planets. They list 10 as "conservative habitable zone" and 11 as "optimistic habitable zone" .

    Only Trappist has about as many planets as the Sun.

    All the "conservative habitable zone" planets out to 40 LY (and further) are Red Dwarfs.

    The "optimistic habitable zone" within 42 LY includes two G stars Tau Ceti, 82 G. Eridani, and two K stars, HD 219134 and HD 40307 (the rest are all red dwarfs). In these cases the planet is the problem more than the star.

    Realistically they haven't found a single planet in 40 LY that really looks habitable.


    True Fs would expand before life got intelligent. Ks and Ms don't produce enough light that can force electrons into the conduction band (photosynthesis) so they have a food shortage, and slower evolution.

    No intelligent life developed in Alaska. It takes a lot of food to feed a large neural network.

    My position is there is about 5000 planets in the galaxy that might currently have intelligent life. The 140,000 number is close enough that I can't discount it - but the lack of anything within 40 LY let alone 22 LY makes me think it is optimistic.

    And we haven't even started discussing star variability, the need for water, a nitrogen atmosphere (for amino acids) etc. etc.
     
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