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I am a writer and I'm building a paradigm wherein the planet Theia did not strike the Earth, but settled into a orbit around the sun a third of the distance between the Earth and Mars. I wanted to ask people in the astronomy field how that might affect the climatic development here on Earth.

I have designed the paradigm where Theia is in a slower rotation around the sun causing periods of time when the two planets will be separated by the sun due to the Earth's faster orbit to being near each other in orbit as the Earth "laps" Theia.

I'm curious how the "waxing and waning" of Theia's proximity to Earth might affect our planet's climate, especially in the near periods. In the story, I assume the development of sentient life and consider how they would experience the possible climatic events when Theia is near. I am wanting to understand the possible range of effects this would have. Would they necessitate alterations in daily life? Would they be dangerous at all? Or would they be cataclysmic in nature?

Also, wondering if anyone would know of a good model to follow describing the actual time between periods of near proximity between Earth and Theia assuming a similar elliptical orbit.

To anyone who responds, I appreciate your time. I want to make sure I get this right or as close to right as possible. I just don't know the physics beyond what I imagine might happen. Thank you all.

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    $\begingroup$ Hypothetical questions like this might be better on worldbuilding stackexchange. $\endgroup$ – antlersoft Jul 28 '20 at 16:11
  • $\begingroup$ Quick back-of-the Wolfram Alpha calculations indicate a close-approach gravitational force at about a third of the gravitational force Venus currently exerts at its closest approaches,which would be pretty much negligible. $\endgroup$ – notovny Jul 28 '20 at 16:12
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    $\begingroup$ I’m voting to close this question because this has been crossposted to Worldbuilding and received answers there. $\endgroup$ – user24157 Jul 28 '20 at 18:26
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    $\begingroup$ There is a nice orbit simulator online that will let you add (or delete) objects in our solar system. Using the size of Mars for Theia and a semi major axis of 1.25 AUs with low eccentricity, you can get a pretty stable orbit but it'd need to run for a long time to see if all else remains stable. The download version crashes for me so I use the browser version. orbitsimulator.com/gravity/articles/what.html $\endgroup$ – AstroShannon Jul 28 '20 at 18:36
  • $\begingroup$ Earth would be more like the Venus. There would be no Moon, no magnetic field. Solar wind had evaporated nearly all the water. $\endgroup$ – peterh - Reinstate Monica Jul 28 '20 at 20:43