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calef comments on Stupid Questions December 2014 - Less Wrong Discussion
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Is there any plausible way the earth could be moved away from the sun and into an orbit which would keep the earth habitable when the sun becomes a red giant?
According to http://arxiv.org/abs/astro-ph/0503520 we would need to be able to boost our current orbital radius to about 7 AU.
This would correspond to a change in specific orbital energy of 132712440018/(2(1 AU)) to 132712440018 / (2(7 AU)). (where the 12-digit constant is the standard gravitational parameter of the sun. This is like 5.6 * 10^10 in Joules / Kilogram, or about 3.4 * 10^34 Joules when we restore the reduced mass of the earth/sun (which I'm approximating as just the mass of the earth).
Wolframalpha helpfully supplies that this is 28 times the total energy released by the sun in 1 year.
Or, if you like, it's equivalent to the total mass energy of ~3.7 * 10^18 Kilograms of matter (about 1.5% the mass of the asteroid Vespa).
So until we're able to harness and control energy on the order of magnitude of the total energetic output of the sun for multiple years, we won't be able to do this any time soon.
There might be an exceedingly clever way to do this by playing with orbits of nearby asteroids to perturb the orbit of the earth over long timescales, but the change in energy we're talking about here is pretty huge.
I think you have something there. You could design a complex, but at least metastable orbit for an asteroid sized object that, in each period, would fly by both Earth and, say, Jupiter. Because it is metastable, only very small course corrections would be necessary to keep it going, and it could be arranged such that at every pass Earth gets pushed out just a little bit, and Jupiter pulled in. With the right sized asteroid, it seems feasible that this process could yield the desired results after billions of years.
I thought this sounded familiar
Hah, thanks for pointing this out. I must have read or heard of this before and then forgotten about it, except in my subconscious. Looks like they have done the math, too, and it figures. Cool!