What would happen if a planetoid with 1/2 Earth’s diameter entered orbit with the Earth and Moon?
Forgetting about the conditions and amount of energy required to successfully capture a planetoid, how would the new planetoid affect the orbits of the Earth and Moon? Would the new planetoid simply become a second satellite, or would all three bodies, being of sufficient mass to affect each other gravitationally, enter into a sort of tri-planetary situation, all three orbiting around a point in space, which would be the point which orbits around the sun?
Eventually if that planetoid crashes into the Earth like the Moon crashed into Earth 4.5 billion years ago, the Earth would speed up in its rotation again and the days will be a lot shorter or about the same length they were 4.5 billion years ago again and we’d have nearly 2000 days in our year again. Other than that, I’m just guessing. Thanks for these 2 points.
Umm. fricking ZoiKS! is how.
Half the diameter and made of rock? That’s a LOT of mass. That’s like Mars stopping by for a quick howdy in the Hill Sphere.
First of it wouldn’t obit us exactly. The two planets would get in to a sort of tango with the smaller one running a larger loop, but even with the Moon we orbit each other. Our gravity and mass would be combined as far as the sun was concerned, so to maintain orbit we would either have to speed up a lot (not going to happen, rather the opposite I’m afraid) or we would have to drift outward to where our velocity, combined mass and gravity are in balance again. Tough to predict where that would be, but probably out past mars.
Hang in there. I am going to model this in “Planets”.
My prediction is that the combined planets will enter a very elliptical orbit and get all cocked up by Jupiter at the Aphelion perhaps crashing in to it during one of its orbits.
The moon doesn’t stand a chance of remaining in the system unless by some freak coincidence it managed to enter a long orbit around both planets. (not likely) Either it:
Crashes in to one or the other planet, or it flies off in to orbit around the sun, or crashes in to the sun.
Hold on…
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Well. If I START a system with with the two masses in a stable orbit (no moon) I can get them to hold just fine. Every time I add a moon in, even if it’s in closer to Earth than ours, it just gets yanked out of orbit in a few revolutions.. Interestingly It seems to leave rather than crash in most cases.
Any time I try to add an orbiting mass to the the already stable Earth / Moon orbit. The moon crashes in to the new planetoid, increases its mass by enough to make the two planets come together (BAD I would think). If I put the new planet out far enough that that doesn’t happen, it gets stolen by Jupiter within a few hundred passes. If that happens the Earth seems to pretty much be okay with it’s moon.
If you actually chuck a planetoid at the system with the correct trajectory to make orbit.. It screws up the WHOLE inner solar system! That’s kinda fun.
You start yanking on Venus and Mercury a bit.
Planets is not especially accurate though.
I do image that there has got to be some lottery in a lottery way that can make the whole thing stable with all three bodies tidally locked, but I can’t find it with my toy modeling program here. Sorry
I can say this. Even if you hit that lottery.. The earthquakes and tides on a daily basis would make things a bit touch and go for humanity.
Tidal effects with the Sun and other planets (particularly Jupiter) would probably render the scenario rather unstable. Sooner or later (and on astronomical timescales, definitely sooner), the Moon and/or the new object would either crash into something else or be ejected into its own orbit around the Sun. The latter scenario might not be that big of an issue for us, provided the new orbit didn’t threaten our own. The former scenario would likely be a gigantic catastrophe.