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I am 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. Thanks, all.

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    $\begingroup$ Hi, there are hypotesis (based on the different amount of isotops distribution in the solar system) that most of Earth water was broght by Theia, which formed in the outer regions. If that were true then it would change massively the climate of Earth making it much drier. But I'll let someone with more knowledge in Astronomy answer this. $\endgroup$ Jul 28, 2020 at 16:51
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    $\begingroup$ Welcome to Worldbuilding! When you have a moment, please take our tour and review our help center to better understand how our site operates. As you might imagine, planetary climate is enormously complex, making this question very broad (as in, it would take volumes of books to answer it in any meaningful way you could select as a "best answer"). Worse, this is a near-duplicate of this question. For both reasons, this question has a high probability of being closed. $\endgroup$
    – JBH
    Jul 28, 2020 at 16:52
  • $\begingroup$ @JBH, I appreciate the welcome and the suggestion. I'll go through the tour presently! I saw that question and thought this was distinct enough to warrant its own answer considering it is adding a new planet-sized celestial body into the mix as opposed to removing a satellite, but I'm new here. I'll leave it for the powers that be to determine. Thank you again! $\endgroup$
    – WeDissent
    Jul 28, 2020 at 17:07
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    $\begingroup$ You want Theia on an orbit at about 1.175 AU. This is dangerously close to Earth, but, assuming the orbits are stable, any effect on Earth climate would be minuscule. $\endgroup$
    – Alexander
    Jul 28, 2020 at 20:34
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    $\begingroup$ Earth not having a moon would have far more impact than Theia being in a solar orbit. As for the relative orbits, any basic orbital mechanics program should give you that. Long-term (that is, billions of years) stability is a more difficult question to answer, as it's to some degree "chaotic" in the sense that actual orbits are subject to sensitive dependence on initial conditions. (And slight perturbations, such as near passes by asteroids & comets/) $\endgroup$
    – jamesqf
    Jul 29, 2020 at 1:35

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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.

On the short term, absolutely not at all. Over the long term, it would affect the precession of the Earth's rotational axis... but you've just removed the Moon by implication, and that's gonna have a much bigger effect, and the alterations in global climate due to changing obliquity and direction of the axis would not be obviously associated with the phases of Theia, occurring on a much, much longer timescale.

For all practical purposes, the presence of Theia in the sky would be utterly irrelevant to climate on Earth. Much more significant are all of the knock-on effects of Theia not having crashed into the early Earth. No Moon. Less mass. Less gravity. Different spin.

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.

You've placed Theia at about 1.175 AU, which will give it a year of about 1.273 Earth years. That's not a whole lot slower, so it will take a long time for Earth to lap Theia in its orbit. The time between closest approaches (the synodic period) end up being about 4.7 Earth years.

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  • $\begingroup$ Do you have an idea on how close Theia would need to be to start having an effect on the Earth and still maintain its own individual orbit around the sun? I had toyed with it skimming the Earth as well in order to keep the moon, mass, and water. $\endgroup$
    – WeDissent
    Jul 28, 2020 at 18:13
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    $\begingroup$ @WeDissent: "How close Theia would need to be to start having an effect on the Earth and still maintain its own individual orbit around the sun?" Not physically possible. Sorry. $\endgroup$
    – AlexP
    Jul 28, 2020 at 18:18
  • $\begingroup$ Earth's climate is influenced on all levels by orbital parameters, short term and long term. Fot example Milankovic cycles. These parameters would be different than present day. So, yeah, there would be differences, possibly drastic. $\endgroup$
    – user78828
    Dec 6, 2020 at 10:13
  • $\begingroup$ I also thought This colliding with Earth was responsible for its current tilt of its axis. This tilt creates or seasons and distributes heat more evenly. That might have a dramatic effect on climate alone. $\endgroup$ Dec 6, 2020 at 14:23
  • $\begingroup$ And by "This" I meant Theia (auto-correct fail). $\endgroup$ Dec 6, 2020 at 14:41
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I asked a similar question about if Theia and Earth orbited each other. Simply, assuming that Theia orbited at the Moon’s distance, it would take 27 days to complete an orbit, and Earth would experience about 4.7 times as much tidal force. That would create tides that exert energy into Earth, causing more tectonic activity, which would increase the frequency of volcanic eruptions and earthquakes. The high tides would flood regions of the globe, while drying out other regions and creating a bit if variety with atmospheric pressures.

The days and nights would last longer, due to tidal locking, and solar eclipses will cast shadows over a larger area. And Theia, with its weaker gravity, will have a more extreme environment. However, the tidal forces will churn liquid iron in the depths of the Earth more, creating a stronger magnetic field. Life there would adapt to the extreme environment, being either able to withstand the conditions for long periods of time, or being agile enough to escape the constant natural disasters.

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