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Featured I Were all these exoplanets a surprise?

  1. Jan 10, 2018 #1

    sophiecentaur

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    For years I have read and heard that the Solar System is there because of angular momentum issues. That is to say, the Sun itself can only rotate at some maximum rate in order to stay intact and the planets are there to equalise the angular momentum of the original nebula and produce a stable star.
    Well, that argument should apply to more or less every other star as it was formed so we should have expected there to be many extrasolar planets. I guess the 'big deal' was actually managing to detect extrasolar planets which was no mean feat. Perhaps the presence of rocky planets and Goldilox conditions is more significant to us, though.
     
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  3. Jan 10, 2018 #2
    I did a quick Google search for Drake fp (fp being the second factor in the Drake equation - the one for proportion of stars with planets). Until recently, astronomers and SETI enthusiasts seemed very hesitant to estimate fp. I did spot a 2011 article were the number 0.4 was tossed out. Of course, the current estimate is pretty close to 1.0.
    As you know, the dynamics of star formation have been sufficiently known for some time. But scientists are hesitant to officially connect the dots without being able to compute some sort of confidence level.
     
  4. Jan 10, 2018 #3

    sophiecentaur

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    That makes some sort of sense but would it not have been real really bizarre to suggest that the Solar system (along with a good engineering explanation for its structure) could have been considered a total oddity? I must say, I never considered the high probability of vast numbers of extrasolar planets myself. I feel a bit embarrassed about that aamof.
    (the year 12011 was sometime after the confirmation of Jupiter sized extrasolar planets so they damned well ought to have considered changing the coefficients)
     
  5. Jan 10, 2018 #4

    stefan r

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    No, not much of a surprise.

    Here is a Sagan lecture: [video] He says "many perhaps even most stars are accompanied by planets" at 2:54. Then writes down 1/4. Then he supposes they all have around 10 planets. I suspect he was deliberately rounding to get 1012 planets in the Milky Way.

    Emmanuel Kant proposed the "nebular hypothesis" in 1755. Kant wrote that he believed there were inhabited planets around other stars.
     
  6. Jan 11, 2018 #5

    Haelfix

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    A lot of it had to do with the numerical models of the time. Where you would model dust, stick it in a box, give it some pseudo random initial conditions and see what the computer would spit out as you modeled the formation of a star and the ensuing solar system.

    You’d get junk most of the time, and rarely did you get many large masses in stable orbits. Most of the time everything would get ejected out.

    Nowadays the models are much more sophisticated and the amount of particles and resolution of the numerics tends to produce solar systems far more readily. Still there is a lot of uncertainty and it’s easy to overtune your software. For that reason many people were skeptical that we had much of a grasp of anything.
     
  7. Jan 11, 2018 #6

    sophiecentaur

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    Considering the early models: Perhaps that would still allow angular momentum to be conserved (?) but it does assume a basic instability. But satellite (and ring) systems around planets seem to keep stable as with the 'shepherding' of the dust by larger items in the rings.
    To cause "everything" to be ejected, conditions would have to be just right, although I can see how some items could be ejected, early on.
    But they had no data to confirm their models or otherwise, I guess.
     
  8. Jan 11, 2018 #7

    mfb

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    Angular momentum is conserved when everything is blown away by the stellar wind. The two things are independent.

    You start with a disk of dust and gas and a very weak star. As soon as the star is fully formed, it blows away all the gas, and most of the dust falls into the star or gets ejected as well depending on its orbit and size. The formation of planets has a very short window (tens of millions of years) - if they don't form before the star reaches the main sequence, they don't form at all. We still don't understand how clumps larger than a few meters form, in the past it was estimated that this happens rarely, which leads to a low estimate for the number of planets.
     
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