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B Earth's twin planet

  1. May 17, 2018 at 3:47 PM #1
    I was watching a really bad Japanese sci-fi movie in which the writers employed a frequent plot device. The Earth had a twin planet opposite the sun which made it undetectable to earthlings.
    This, of course, would be possible if the Earth's orbit was a perfect circle, which it isn't. It is, of course, elliptical.
    Question: Given that the Earth's speed in it's orbit varies according to its distance from the sun, would a planet opposite the Earth always maintain its position behind the sun?
     
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  3. May 17, 2018 at 3:54 PM #2

    Orodruin

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    In the ideal case that the Sun's gravitation was completely dominant and the eccentricities and radii were the same and their perihelion positions were on opposite sides of the Sun, yes. Now, any perturbations to this (such as the influence from other bodies in the solar system) would accumulate over time and break this situation, not to mention that you could discover the opposite planet using spacecraft.
     
  4. May 17, 2018 at 3:59 PM #3
    Thanks for the quick reply.
    I'm new to this forum and am looking forward to future discussions, etc.
    I didn't mention the obvious about discovering the planet with satellites or spacecraft because this was a very bad Japanese movie from the 60's
     
  5. May 17, 2018 at 8:34 PM #4
    Well it might not have been as bad as you think considering that western sci fi movies at the time were concentrating on super heroes with magical powers.
     
  6. May 17, 2018 at 8:54 PM #5

    stefan r

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    I do not think circular orbits matter. Could be an extremely elliptical orbit, like a comet. Just has to be perfectly opposite.

    You can hang out at 5 Lagrange points. Only L3 is on the far side of the sun.

    There is also an asteroid called 3753 cruithne which has a 1 year orbit around the sun.
     
  7. May 17, 2018 at 10:03 PM #6

    Janus

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    The problem with the L3 point is that it is unstable. The slightest drift from that perfect balance point and the combined gravity of the sun and Earth will tend pull it even further out of position. This is unlike the L5 and L4 points, where a slightly dislodged object will tend drift back into place.
     
  8. May 18, 2018 at 4:52 PM #7
    Not to labor the point but Hollywood produced some sci fi clunkers in the 50's excluding the classic Plan 9 From outer Space.
     
  9. May 18, 2018 at 7:10 PM #8

    stefan r

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    A trip to the moon dates to 1902.
     
  10. May 18, 2018 at 8:40 PM #9
    Very interesting, though somehow I got a psychedelic 60's impression of it.
     
    Last edited: May 18, 2018 at 9:03 PM
  11. May 19, 2018 at 9:18 AM #10

    JMz

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    Back on the OP: The Earth's Twin's gravity will also perturb the orbits of the inner planets. My guess is that, even as early as the 19th Century, people would have easily been able to deduce its presence from them.

    This is the same story as the discovery of non-Newtonian effects on Mercury's orbit and of Neptune itself, both of which were indeed detected in the 19th C (though people didn't know what to make of Mercury's orbital anomalies at the time). However, I don't have the numbers for an Earth's Twin.
     
  12. May 19, 2018 at 3:29 PM #11
    Briefly, I don't have a degree in Physics. I credit Carl Sagan's Cosmos for igniting my interest in it and Cosmology. Your reference to Lagrange points got me to look it up. I had heard something about them, but that's about it.
    The material I read mentions the GAIA satellite at L2. I had heard of GAIA but not exactly what it does.
    I subscribe to a YouTube channel Space Time. Those guys are awesome. Their short lectures are captivating although a little hard to follow sometimes. And sometimes the material is a little over my head.
    Gabe's series on General Relativity is, as promised, mind blowing.
    I recently watched one on GAIA'S contribution to Astrometry. Wow is about all I can say.
    BTW, thanks for your reply.
     
  13. May 19, 2018 at 7:44 PM #12

    JMz

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    Gaia is in a (gravitationally) unstable Lagrange point. It is actively stabilized by non-gravitational means. Like being on the top of a hill, gravity works against staying there, but it's a lot easier to keep yourself in place there, with small forces, than to keep yourself in place on the side of hill, where you need much larger ones.
     
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