Okay, I’ve got a moderately large scale spatio-civil engineering project I’d like some advice on.
Say I wanted to add another planet to our solar system—basically, a duplicate of Earth in size, composition, and habitability.
Now, assuming I can teleport it to our solar system instantly, at any location and velocity required, is there any good place to put it where it could remain habitable, and not screw up the orbits of any other planets or astronomical bodies (the principal aim being avoid Earth-shattering kabooms)?
I’m not sure if the Trojan points (60 degrees in front of or behind the Earth) are stable when both bodies are of the same size or not. I seem to recall they aren’t. But it might work if you put two planets in. Put a very large Jupiter-like one in Earth’s orbit and have the Earth and its twin 60 degrees in front and in back.
If it’s “a duplicate of Earth in size, composition, and habitability,” then it would have to be in Earth’s orbit . . . probably exactly opposite us, on the other side of the sun. Otherwise it would fail the “habitability” test.
IIRC, orbiting on the other side of the Sun isn’t actually stable.
It might work if you put it next to Mars, with them orbiting around each other. Especially if you are willing to tweak the definitions of “size, composition, and habitability” a bit; as I understand it the orbit of Mars is thought to be on the edge of the potentially habitable range, if Mars was a bigger planet. You might be able to end up with a cold but life bearing terrestrial planet, with some extra carbon dioxide say.
True. I recall the SF flick from 1969, Journey to the Far Side of the Sun aka Doppelganger, a film that didn’t age well. Wikipedia has a nice article on the Counter-Earth, a concept first proposed in the 5th century BC.
Followup question: is there a cheat? Could an earth-sized object circle the sun at about 1/3 the distance to Mars (or Venus) without messing up our orbit? Presumably we could tamper with CO2 levels or ocean volume at the margin to create a more temperate climate. We could also limit settlement to certain latitudes.
What you want is to have the planet be co-orbital with the Earth. That is, put the other planet (let’s call it Planet P) in an orbit that’s slightly further from the Sun, say about 50,000 km. The Earth will orbit slightly faster and eventually catch up to Planet P. When it does, its gravity will pull back on P, which will move P into a lower orbit. P’s gravity will pull the Earth forward, which will move it into a higher orbit. Presto, the planets have swapped orbits. Now Planet P is moving faster and it will eventually catch up to Earth and things will repeat.
I suspect you’d have to make the Earth’s orbit almost perfectly circular in order to make this a stable system. But if you have the capability to teleport a planet, nudging their orbits around should be a piece of cake.
There’s also the possibility that perturbations by the other planets could eventually destabilize the orbits, so some long term monitoring would be desirable.
Note that the planets won’t actually get very close to each other during the orbit swap, so you don’t have to worry about earthquakes or unusual tidal effects. Unless of course it was done by Hollywood, in which case Civilization will be in danger of collapsing every time a swap takes place… (don’t worry, I’m sure Bruce Willis will be available to save the day).
The Lagrange point on the exact opposite side of the orbit from the Earth (or any other) planet is not stable so perturbations would not likely let such an arrangement last. The Lagrange points 60 degrees ahead and behind the Earth (or another planet (the so called Trojan points) are stable at least for much smaller third bodies.
IIRC stable is a relative term. IIRC our solar system as currently configured is only good for a few billion years (maybe even just a fraction of that) before something crashes into something else or get flung sunwards or starwards.
Or, in other words, how long does it have last?
I think the coorbital answer is the best so far…but the earths moon is probably going to screw that up. With tweaking, coorbital with mars or venus is probably a better bet.
Yeah, it probably will. From a far enough distance, you can treat the Earth-Moon as if all its mass is located at its barycenter, and things will be copacetic. But get close enough, and that doesn’t work. I don’t know how close a coorbiting planet will get, but it’s almost certain to be too close. So you have a 4-body problem (Sun, Earth, Moon, Planet P) which is likely to be unstable.
OK, so the Moon has to go. Sorry old Moon, but you know how it is – got to move with the times. Hey, now don’t be feeling glum. We had a whip-around among the other Solar System bodies and got you this nice watch. Plus we put an ad in the Galactic Times to see if some other star system has an open position that you qualify for. I’m sure we’ll be getting a reply to it any day now…
I’m not sure I’d want to live on a planet at either of those distances from the Sun. Mars is a nice place to visit, but…