Habitability properties of circumbinary planets:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jan 19, 2017.

  1. paddoboy Valued Senior Member

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    https://arxiv.org/pdf/1701.03475.pdf

    Habitability properties of circumbinary planets
    12 Jan 2017


    Ivan I. Shevchenko∗
    Pulkovo Observatory of the Russian Academy of Sciences,
    196140 Saint Petersburg, Russia



    Abstract:
    In this article, it is argued that several habitability conditions (in fact, at least seven such conditions) appear to be fulfilled automatically on the circumbinary planets of main-sequence stars (CBP-MS), whereas on the Earth these conditions are fulfilled only by chance. Therefore, it looks natural that most of the production of replicating biopolymers in the Galaxy is concentrated on CBP-MS of particular classes, and life on Earth is an outlier, in this sense. In this scenario, Lathe’s (2004) mechanism for the PCR-kind (polymerase chain reaction) tidal abiogenesis on the Earth is favoured as generic for CBP-MS. Unsolved problems of the scenario are also discussed.


    Conclusions:
    Circumbinary planets are generic: indeed, a lot of circumbinary planetary systems have been discovered up to now, and cosmogonical simulations show that the formation of such stable systems is a natural process (see, e.g., ref. [25] and references therein). On the other hand, double planets are nongeneric: the probability for the Earth-like planet to acquire a large Moon-like satellite, from the cosmogonical viewpoint, is extremely low [51]. As we have seen, striking analogies exist between the habitability conditions on CBP-MS and on the Earth. In fact, in favouring the habitability conditions, the Earth seems to mimic a typical CBP-MS. CBP-MS, especially, CBP of M-dwarf twins, seem to be generic in providing such conditions (i.e., the conditions arise automatically), whereas the Earth is not (i.e., the conditions arise accidentally). Therefore, the revealed multiple analogies between CBP-MS and the Earth may indicate that life on Earth is a low-chance outlier of a generic global chemical process (massive production of replicating biopolymers) concentrated on CBP-MS. In this scenario, Lathe’s mechanism [4, 46] for the PCR-kind tidal abiogenesis on the Earth is favoured as generic for CBP-MS
     
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  3. paddoboy Valued Senior Member

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    Wow! that is certainly an eye opener, interesting scenario!
    While Earth obviously having a relatively large Moon, that was a lot closer in the past, which probably was conducive to "Tidal abiogenisis", yet still an accidental, low chance scenario, when compared to the more favourably induced circumbinary planets.
     
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  5. paddoboy Valued Senior Member

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    A couple of interesting excerpts from the paper.......
    "Most of the observed CBP-MS are indeed close to the habitability zone [16]. As we have just seen, this is not a mere coincidence, but an inevitable consequence of generic dynamical and physical effects"

    and......
    Tides
    " The importance of tides for abiogenesis is at least twofold: first, they produce periodic wetting and drying of beaches, and this process is favourable for life in several respects [4]; second, they provoke plate tectonics, also favourable for life in several respects, in particular, by letting important chemicals produced deeply in planetary interiors to come to its surface [6]. According to ref. [4], life on Earth has, in fact, a tidal origin. As discussed in Section 1, most observed CBP-MS reside in resonance cells delineated by the chaotic bands corresponding to the 5/1, 6/1 and 7/1 mean motion resonances with the central binary. Therefore, the typical ratio of the orbital periods of the planet and the binary is ∼6. Since the stellar binary components usually have comparable masses, the Fourier expansion of the time-varying gravitational potential acting on the planet possesses a dominating term with the doubled frequency. If the masses are equal, then the period of neap/spring tides on the planet effectively doubles, i.e., the ratio of the tide frequency to the planet orbital frequency is ∼12, analogous to what we have (at present) on the Earth subject to the Lunar tides. The repeatedly drying-wetting tidal pools are thought to be a possible place for originating of self-replicating biopolymers, as such pools provide favourable conditions for concentrating organic molecules (see ref. [4] and references therein). Lathe proposed a theory [4, 46, 47] of abiogenesis, based on a tidal “boosting” of the biomolecules production in near-shore lakes and ponds. The essence of the theory consists in the hypothesis that periodic concentration/dissociation of complex molecules leads to a “chain reaction” in production of specific nucleic acids. An open question with this theory is that it postulates frequent and high tides, not characteristic for the modern Earth and, presumably, for the early Earth as well [47, 48]. Besides, the rates of concentration/dissociation are not determined quantitatively. The rates of evaporation in modern lakes are of the order ∼1 cm/day maximum [49]. They are controlled by the processes of the Solar energy storage in the lakes’ water. Therefore, much more time than just several hours, as in Lathe’s original theory [4, 46, 47] might be needed to concentrate the “bio-soup”
     
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  7. youreyes amorphous ocean Valued Senior Member

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    You are replying to yourself?
     
  8. paddoboy Valued Senior Member

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    I'm expressing my thoughts on an article I find highly interesting.
     
  9. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    Interesting stuff.
    I understood that the energy that circumbinary planets receive will vary quite consdiderably during its year, causing many more "seasons" than on Earth (assuming a similar length of year), due to the relatively quick orbit of the two Suns around each other. If so, would the environment not be too dynamic for abiogenesis to take hold, especially if the tidal system is being seen as quite important?
    That said, the point of evolution is that it effectively filters out all those that can't adapt, or adapt quickly enough, so life on such a planet might be either supremely adaptable or simply viable in a wide range of conditions.
     
  10. paddoboy Valued Senior Member

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    That seems a good point to make.
    Perhaps though a happy medium would though probably be more favourable for abiogenisis to take hold.
    It wasn't so long ago that most scientists would have thought that multiple star systems were far less likely for abiogenisis.
    It also illustrates if their premise is valid, how important our Moon is.
     
  11. iceaura Valued Senior Member

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    I doubt their rate of evaporation of lakes is reliably meaningful or extrapolated - wind, for one thing, would have many more and often considerably stronger drive regimes, with implications for waves etc. as well as evaporation. Splash zones would do for tides. As far as seasonal variability, most of the earth doesn't have much or feel it at all, with gradation to the more affected regions - and that gradation would presumably hold for a multiple season regime.

    Where too much variability might kick in hardest might be the transition to multicellularity, or large size. Once over the hump though, if it's there, size and complexity would presumably be an advantage in dealing with variability.

    This entire hypothesis startles.
     

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