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A New Planet

  1. Oct 27, 2007 #1
    Imagine if there were another planet similar in mass and volume to earth on a parallel orbit, on the other side of the sun.

    Would such a planet disturb the equilibrium of the solar system?

    And if there were indeed such a planet, how would its existence be known to humans?

    I believe conventional equipments, like telescopes would be useless, and even satellites would not be of any help.

    How would we know it's there?
  2. jcsd
  3. Oct 27, 2007 #2
    I have not found out how humans could detect the 'other planet'. If so, there's a very small possiility of its existence NOW.
  4. Oct 27, 2007 #3


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    I don't think we would know it is there, but it would need to be on precisely the same orbit as the earth to avoid detection from earth, which would be extremely unlikely. Also, such a thing would be unstable. Jupiter perturbs our orbit enough to make a precise alignment unlikely and temporary. So we'd need to have several simultaneous one-in-a-billion coincidences for such a thing to exist and be invisible now.

    I don't think it could evade SOHO, though (not sure).
    Last edited: Oct 27, 2007
  5. Oct 27, 2007 #4

    D H

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  6. Oct 27, 2007 #5
    Thanks Russ and Pixel

    To DH: Ok....so if I understand correctly, what you're implying is, generally speaking the paths of near-Earth asteroids would go awry, maybe even crash into the twin planet, or maybe the twin planet would mess with their trajectory enough to cause them to eventually crash into Earth, or the near-Earth asteroids would maybe end up going up somewhere where they wouldn't have.

    For a moment, let's imagine that said twin planet wasn't there and it suddenly appeared out of nowhere.

    Query: What would the chances be of near-Earth asteroids crashing into Earth and if so how much time would we have? Of course, I know it all depends on when the planet would "pop up" so let's say it popped up on December 31, 2007. What then?
  7. Oct 27, 2007 #6
    Such a planet would perturb the motion of other planets in a detectable way.

    The orbits of the planets are the way they are because of resonance. This configuration would disrupt the resonance, meaning that planets would not have the configuration they do.

    Because of the eccentricity of the earth's orbit, the earth's angular velocity is different in different parts of its orbit. I don't beileve it is possible for a planet to orbit exactly oppositte from us. There will be times during the orbit where the planet must be visible (from space, at least).
  8. Oct 27, 2007 #7


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    Absolutely no way of predicting.

    But in general, longer times are more plausible than shorter times. Perturbations tend to "nudge" rather than "throw", and tend to be cumulative, so small nudges would accumulate over years or centuries.

    OTOH, in a natural system unstable orbits are unlikely over these longer periods (because they would have already crashed or been flung or whatever).

    The upshot: if a planet popped into existence, the NEOs would begin drifting from their predicted orbits right away. We'd get increased near-misses but in the emptiness of space (even in the inner solar system) near-misses vastly outnumber hits. It could be years or centuries of increasingly frequent and increasingly close fly-bys before a hit.
    Last edited: Oct 27, 2007
  9. Oct 27, 2007 #8


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    The premise is that the other planet is exactly opposite both in radial angle and eccentricity. That would make it perfectly mirror Earth's position and velocity at all times.
  10. Oct 27, 2007 #9
    To Russ:

    What quality should the twin planet possess to near-neutralize Jupiter's alignment-perturbing ability? that is, to render the "misalignment" extremely insignificant. I'm aware this question might sound dumb. Let's say, I'm a recent convert to the fascinating world of astrophysics, but believe me you, these queries are for an important reason, and I would be very grateful for any help you provide.
  11. Oct 27, 2007 #10


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    We're guessing you're writing a story.

    Problem with sci-fi plots of this nature is that they become so tortuously contrived as to be rendered unbelieveable. What's the point on writing a story that could never happen?

    There is nothing a planet could do to cancel Jupiter's effect.
    Last edited: Oct 27, 2007
  12. Oct 27, 2007 #11
    To Mawm:

    I'm still a novice at this, but I have to ask you this, said twin planet would disturb the other planets as much as Earth does which, if I assume correctly, is trivial.

    Query: Would said disturbance of the resonance be catastrophic and if so what kind of timeframe are we talking about?
  13. Oct 27, 2007 #12
    To Dave:

    Your guess is almost right. Some of the best science fiction plots are contrived. And fiction is what it is: Fiction. I'm not going to use any cliches here, but all fiction requires a certain degree of supension of disbelief.

    But I am extremely grateful for the help that I've received, and especially from you Dave.

    Any more insights into the matter would be greatly appreciated.
  14. Oct 27, 2007 #13

    Jonathan Scott

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    See the Wikipedia entry on "Counter-Earth", especially the "Scientific Analysis" section.

    This was also part of the idea behind the 1969 film "Doppelgänger" (in which the alternate Earth was a mirror image but otherwise identical - which doesn't make any sense scientifically, but made for an interestingly confusing plot).

    I would guess that with various space probes scattered around the solar system and routine observations of asteroids and similar, if a new Earth-sized planet suddenly appeared it would not take long for the astronomical community to notice that something odd had happened (perhaps just a few weeks). Even if its orbit started off as diametrically opposite to that of the Earth, I think that disturbances from Jupiter and other planets would be sufficient to break the symmetry within a very small time on the astronomical scale.

    I guess what you'd need in order to find out more details is a solar system ephemeris computation model which allows you to add a new planet and determine the results.
  15. Oct 27, 2007 #14
    Even though the gravitational effect is small, like Dave said, it is cumulative, so it adds up. I can't be sure of the time scale, but certainly that planet couldnt have been here all along. If it just popped into existence, I can't say how long it would be before its orbit was disrupted. As others have pointed out, the first effect we would probably see is the disruption of orbits of asteriods. I'd think that would be noticable within a year or two.
  16. Oct 28, 2007 #15


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    If an identical Earth magically materialized at Earth's distance, on the opposite side of the Sun, it would be in Earth's Lagrange 3 (L3) point. Mathamatically it can stay there forever if nothing perturbs it away, just like mathamatically you can demonstrate that it's possible to balance a sharp pencil on its tip. But try balancing the pencil in real life, and you'll find it impossible to do.

    Similarly, the anti-Earth would not stay put for very long. It will roll off the L3 point towards either L4 or L5, and swing around L4 or L5 back to L3. If it crosses L3, it will next visit the L4 or L5 on the other side, and repeat this over and over again in what is known as a horseshoe orbit. If it fails to crest the L3 point, it will continue to loop around the L4 or L5 point in what is known as a tadpole or trojan orbit. In all cases it will be in a 1:1 resonance with the real Earth, and will make repeated close passes to the real Earth every few hundred years. This will cause both planet's eccentricities to rise to high values, which would have a huge effect on our climate. It would also ensure that history was filled with apparations of a mysterous planet that grew large enough to resolve with the naked eye, then retreated as quickly as it approached. To me, that would make very interesting si-fi.

    Additionally, it only takes a very small pertubation to make the system jump from a trojan state to a horseshoe state.

    As others have stated, it would be very easy to detect its presence by the way it perturbed the other asteroids or planets. The pertubations on the asteroids that DH mentions would be very noticable. And you can add to that list the Spitzer Space Telescope, whose position is extremely well known as we are constantly communicating with it. Spitzer is in a 1:1 horseshoe orbit with Earth.

    And even though its perturbations on other planets would be trivial as Blackwing points out, our ability to detect this is far from trivial. We'd notice within a few weeks that Mars and Venus were not exactly where they should be.

    Here's an animation of a Venus-mass planet placed directly on Earth's L3 point. Originally the Venus-mass planet dropped off the L3 point into an L4 trojan orbit. Later it was perturbed into a horseshoe orbit. The animation shows one cycle of the horseshoe state looped over and over again:

    Here's a link to a thread describing the simulation that made this animation: http://www.orbitsimulator.com/cgi-bin/yabb/YaBB.pl?num=1189814191
  17. Oct 28, 2007 #16

    D H

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    SOHO's halo orbit around the Earth's L1 point brings it about 6.7x108 meters away from the Earth-Sun line, a tiny bit smaller than the Sun's equatorial radius. The planet could thus still hide visually from SOHO, but the planet would need very good guidance, navigation, and control to do so. Since the L1 point is unstable, the presence of an Earth twin opposite the Sun would perturb SOHO's orbit. The planet might be able to hide from SOHO visually, but it could not hide from the havoc it wreaks on SOHO's orbit.
    Last edited: Oct 28, 2007
  18. Oct 28, 2007 #17
    Tony, that was brilliant!!

    I'd like to know if there is a software that I could get which would enable me to run simulations of an extra body added to the solar system?
  19. Oct 29, 2007 #18


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    I used Gravity Simulator ( www.gravitysimulator.com ) which is a program I wrote. Yes, you can add extra bodies and check for stability.
  20. Oct 29, 2007 #19
    This is a wonderful thing you've got here, Tony. Hats off to you!!

    I was wondering if there are any similar high-tech softwares out there. Don't get me wrong, your program is going to be of big help for the fundamentals, but I have to make an appealing presentation to some people, and frankly speaking, I don't want to involve any third-party special effects team just yet, that is, until I've got everything clear myself. Any suggestions?
  21. Oct 29, 2007 #20


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    That's exactly the kind of thing I was getting at - I wasn't sure how precise and stable SOHO's positioning was. Thanks.
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