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Thread: 2 Earths in one orbit around the sun, the effects?

  1. #1 2 Earths in one orbit around the sun, the effects? 
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    Hello,

    This is my first question post. And i had the idea for a short story to have two Earths rotate around the sun in its same orbit. I have absolutely no idea what kind of (magnetic) traces we leave behind in our orbit around the sun.

    Think about a clock comparison, I already checked we rotate counter clockwise around the sun. We are at 9 o'Álock. Earth 2 would be at the other side, 3 o'clock. What would the effects be?

    Are we leaving behind any traces like a wake behind us. Think about two boats that continuesly sail in a circle, like the clock comparison. In some way both boats would be effected by the wake from the other one. And at some point, they would devert slightly from their path. Though both captains would take the effort to keep them on the same place.

    Question number two and three: Example stated above is when two planets are at two opposite points having the sun inbetween them.

    2) What would happen in the same example, where Earth 2 would be placed at 12 o 'clock? Earth 2 would then be "behind" us, since we both rotate counter clockwise around the sun.
    3) What would happen in the same example, where Earth 2 would be placed at 6 o 'clock? Earth 2 would then be "in front" of us.

    I kinda like the idea as part of an sci-fi story and i think the possibilities to create a cool story from this alone are enormous.

    Bye.


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  3. #2  
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    There are no traces or wakes. The mass of the earth is not significant in relation to the mass of the sun, so the two earths would have no noticeable effect on one another, at least in the short term. I don't think this is a stable configuration, though. One or the other would start going a little slower than the other, due to meteor impacts and such and eventually they would collide.

    I don't understand your other questions. If they are on directly opposite sides of the sun, neither is ahead or behind the other. What is your reference point for determining the "o'clock" position of the planets?


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    I think he might be referring (though with the wrong angles) to the forward and behind Lagrangian points L4 and L5 (Which are not truly stable).
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    Hi, thanks for answering my question. To add some info to the other question.

    In example one, both planets would be opposite to each other with the sun in the middle. (Like the numbers 12 and 6 on the clock )
    In example 2, that distance would be shorter, placing one planet closer to each other. And back to the clock, 1 would still be on 12, but now the other would be on 3.

    By telling me that one of them would eventually collide with the other you kinda answered all my questions.

    Thank you.
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    Harold14370 is correct that the configuration would not be stable. Once either planet is slightly disturbed, such by being perturbed by other planets, etc., they will begin to drift together. However, they will not collide. Instead they will go into what is sometimes called a "horseshoe orbit", so called be cause as seen from the perspective of one planet, the other planet follows a horseshoe shaped path.

    Here's what happens:

    One planet slows down or speeds up. After a while, the two planets begin to approach each other. as they do so, their mutual gravity starts to pull on each other. The lead planet pulls forward on the trailing planet and the trailing planet pulls back on the lead planet. This adds orbital energy to the trailing planet and subtracts it from the lead planet. This causes the trailing planet to climb into a higher slower orbit and the lead planet to fall into a lower faster. The lead planet now has the faster orbit and begins to pull away from the trailing planet. Eventually, it will catch up to other planet from behind, taking on the role of trailing planet, and the process repeats.

    This is how it appears from one of the planets:

    The other planet approaches from "behind" in a slightly closer to the Sun, it gets so close, and does a U-turn climbing away from the Sun as it does so. It then travels all the way around the Sun, until it begins to approach from "in front" in a slightly further from the Sun until it does another U-turn, dropping in closer to the Sun. It travels around the Sun again in the opposite direction (it doesn't really change orbital direction, this is just relative to the first planet), until it once again approaches from behind. This is the "horseshoe".
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    And we will all die? I can imagine what each others gravity disturbances can cause...
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    Quote Originally Posted by kelleskurter View Post
    And we will all die? I can imagine what each others gravity disturbances can cause...
    No. The planet's will not approach each other any closer than the distance of the L2 Lagrange point, (at a minimum, it might not even be this close) which is ~1,500,000 km. Any gravitational disturbances that we will see will be due to tidal forces, which fall off by the cube of distance. The Earth is 81 times as massive as the Moon, but 1,500,000 is ~3.9 times further than the moon which cubed is 59.6.

    81/59.6 = 1.36, which means that the tidal forces would be only 1.36 times more than the moon's at their largest. No mass extinction of mankind, just some adaptation to higher tides.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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