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Insights Either the Sun Is Getting Smaller or Gravity Is Getting Weaker

  1. Apr 8, 2018 #1

    klotza

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  2. jcsd
  3. Apr 8, 2018 #2

    fresh_42

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    Very interesting. There's a minor LaTeX error after "77,000,000,000".
    And last but not least a good reference to quote on the FAQ "Do constants change over time or space?"
     
  4. Apr 8, 2018 #3

    JMz

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    To one point: The Solar System -- the orbital radii of the planets and other bodies -- could be getting larger as the Sun's mass slowly shrinks. However, it could also be getting smaller, due to friction from the solar wind. (Also radiation pressure, in the case of tiny bodies, especially dust.) The getting-larger effect should apply equally to all bodies, and the increase should be a simple proportionality with distance. But the getting-smaller effect(s) should be greater at smaller solar distances and for less dense bodies. Which effect is dominant, and for which bodies?
     
  5. Apr 8, 2018 #4
    Really enjoyed this Insight!
     
  6. Apr 8, 2018 #5

    mfb

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    There is also one at "1026 Watts"

    > Together, the predicted mass loss rate is consistent with the measured decreasing gravitational parameter given its uncertainty.
    So... we expect a mass loss, and we see the effect of the mass loss in the expected amount. Nothing surprising, unlike the topic would suggest.
     
  7. Apr 8, 2018 #6

    Drakkith

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    Some would hope the Earth's gravity is getting weaker. It would certainly make people feel better after the end of year holiday dinners. :biggrin:
     
  8. Apr 9, 2018 #7
    Well isn't the momentum of the solar wind directed, for the most part, directly away from the sun? So it would contribute to an expansion overall, yes? Perhaps when the charged particles interact with magnetic fields of (some) planetary bodies and they're deflected? But still seems like an "outward" directed force.
     
  9. Apr 9, 2018 #8

    mfb

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    A uniform outwards force does not increase orbits, it gives them a different period. It acts like a slightly lower (but constant) solar mass. What is left is some sort of friction, which decreases the orbital radius of objects over time.
     
  10. Apr 11, 2018 #9

    Chronos

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    Isn't sixty parts per quadrillion decrease in gravity per year smaller than the uncertainty in the gravitational constant given by CODATA?
     
  11. Apr 11, 2018 #10

    mfb

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    Yes. So what?
    What astronomers measure is not the gravitational constant, but the product of the gravitational constant and the mass of objects, GM. This product can be measured much more precisely than either G or M.
     
  12. Apr 12, 2018 #11

    JMz

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    Yes. So in principle, the title of this thread is misleading: The product is decreasing, but (a) it could be either or (b) it could be both or (c) one could be increasing slightly but the other decreasing more.
     
  13. Apr 20, 2018 #12

    fluidistic

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    I'm curious if they took into account the momentum of the EM field (or photons) created by the Sun exerted on the planets (and the black body radiation of the planets and cosmic background blackbody radiation). By intuition, even though Mercury is a small planet, it's very close to the Sun and might be the most affected to it.
     
  14. Apr 20, 2018 #13

    JMz

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    This is covered by @mfb's post #8 here (even though that was stated in the context of the solar wind).
     
  15. Apr 26, 2018 #14

    Chronos

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    It is very difficult to draw any meaningful conclusions about individual factor variance based on the product of individual factors across cosmological time scales.
     
  16. May 1, 2018 #15

    fluidistic

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    Does this mean that if the Sun was, say, so shiny that the outward force more than counteract the gravitational force between the Earth and the Sun, the Earth would still have its orbit intact?

    I do not understand how the Earth could stay with the same orbit if the photons hitting them from the Sun were so much more numerous than they are now that the outward force would be so great that there should not be any stable orbit. Am I missing something?
     
  17. May 2, 2018 #16

    mfb

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    No, of course not. These particles are not in an orbit at all. That only affects particles smaller than ~500 nm, however.
     
  18. May 2, 2018 #17
    Has anyone calculated the loss of energy from the gravitational waves emitted by the Sun and Jupiter, or the Sun and the other gas giants?

    For the Sun and Jupiter,

    m1 = 1.989 × 10^30 kg (Sun) ~ 2 × 10^30 kg
    m2 = 1.898 × 10^27 kg (Jupiter) = 0.0009543 m1 ~ 2 × 10^27 kg
    R = 778.5 million km = 7.785 x 10^11 m ~ 8 x 10^11 m

    The best reference I could find with a quick Google search was:

    http://www.physics.usu.edu/Wheeler/GenRel2013/Notes/GravitationalWaves.pdf

    but I'm not familiar enough with the formulas to be confident that I'm applying them correctly.
     
  19. May 2, 2018 #18

    mfb

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    About 200 W for Earth/Sun, a bit more for Jupiter. Wikipedia has formulas where you can just plug in masses, distances and eccentricities (use e=0 for a good approximation).
     
  20. Jun 4, 2018 #19

    TZT

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    Some of you likely already know some of the following, but it was a very interesting point, about the Sun, when I heard it.

    Jupiter is massive, and so is the Sun. Given the mass of Jupiter it has great total gravitational force. That force also is exerted noticeably on the Sun itself.
    Due to the gravitational force of Jupiter it actually affects the Sun's position in our solar system, such that the Sun is not in a constant epicenter where all the planets form their orbits around that constant point. Rather, Jupiter's gravity pulls on the Sun such that the Sun also has an "orbit", and it's orbit is around an imaginary point that the sun orbits around. So, the Sun itself is also pulled towards Jupiter as Jupiter is pulled towards the sun, and their respective gravity creates both Jupiters's orbit as well as giving the Sun an "orbit" that is around the "center" of the solar system.

    Very cool. And it demonstrates the massive gravitational power of Jupiter.

    Question:
    As the Sun's mass lessens, and with that it's gravitation force lessens, then at what point in the future will Jupiter's gravity have a greater effect on the planets between it and the Sun? IOW, at some future point, will Jupiter's gravitational effect become stronger on the Earth as the Sun's gravitational effect becomes lesser? And, when, or if, that happens, will the Earth's orbit change? Will the effect of Jupiter's gravitational pull slow the Earth's orbit around the sun? Or, can it create an effect of a slow orbit during certain Earth to Jupiter orbiting positions, and then speed up the orbit during different relative positions?

    This of course is predicated on the idea that the Sun's mass is lessened due mainly to fusion and mass coronal ejections, while Jupiter's mass remains constant over this same period.
     
  21. Jun 4, 2018 #20

    PeterDonis

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    This is true of all the planets, not just Jupiter. Jupiter's effect is by far the largest, but I don't think it's the only detectable one. The strictly correct statement is that all of the objects in the Solar system orbit its barycenter, which can be thought of as the "center of mass" of the system as a whole, and this barycenter does not coincide with the center of any of the objects, including the Sun.

    Never. The rate of mass loss of the Sun is much, much too small. The sun is over 1100 times as massive as Jupiter, and the mass loss rate is roughly 6 parts in ##10^{14}## per year, so even after 5 billion years more, when the Sun is expected to become a red giant, the Sun will have lost only about 1 part in 100,000 of its current mass, so it will still be over 1100 times as massive as Jupiter.
     
  22. Jun 4, 2018 #21

    TZT

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    Soooo, you're sayin there's a chance!? LOL.

    Thanks for the answer.
     
    Last edited: Jun 4, 2018
  23. Jun 4, 2018 #22

    TZT

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    Well now, of course Jupiter's gravity affects all the planets, as all the planets can affect each other. But now, that wasn't the point, and that's not what I was asking or talking about.

    [Moderator's note: rest of post deleted as it was off topic.]
     
    Last edited by a moderator: Jun 4, 2018
  24. Jun 4, 2018 #23

    PeterDonis

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    It appears that I did address what you were asking and talking about. So the rest of the argument about this subthread is pointless, and I am deleting it.
     
  25. Jun 5, 2018 #24

    mfb

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    Both Jupiter and Saturn contribute notably to the position of the Sun relative to the barycenter of the Solar System. Saturn has a smaller mass but the larger distance means it still plays a relevant role.

    Wikipedia has an image - the 12 year period comes from Jupiter and the perturbation of that cycle comes from Saturn, with smaller contributions from other planets.
     
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