Is it possible for humankind to divert Earth off its orbit around Sun?
August 7, 2013 10:18 AM   Subscribe

I know it is a funny thought but I am curious. For instance, the mega-quakes can speed up or slow down self-rotation of Earth, albeit minutely. So in a similar vein would it be possible for a group of wacko scientists to get Earth off its orbit around the Sun to freezing cold in outer space by means of technology and materials? Can this idea be proved to be possible or not? Or maybe it was discussed earlier somewhere on Intertubes and you can help me find it.
posted by raphael19 to Technology (12 answers total) 1 user marked this as a favorite
Best answer: The short version, no, nothing that is known to be within the capabilities of human beings will have a meaningful impact on the Earth's orbit.

The longer version is, well, sure, anything that pushes on the Earth will have an impact - every tiny meteorite that hits the Earth pushes it a tiiiiny bit. That's basic physics. So, if you want to imagine some kind of MagicMegaBomb, you could just detonate that anywhere on the Earth's surface, direct the blast "down," and see the Earth move.

The physics of "how do I move the Earth" is very straightforward; absolutely any force upon the Earth does it; for every action there is an equal and opposite reaction. There's really no need to prove that; it's very basic Newtonian physics. But the amount of energy required is so far beyond current human capabilities that it's absurd, even setting aside the difficulty of doing it in a way that wouldn't wreck the continents, end all life on Earth as we know it, heat things up too much for the ecosystem to function, etc.
posted by Tomorrowful at 10:26 AM on August 7, 2013 [1 favorite]

Best answer: This will be a question of imparting sufficient kinetic energy to the Earth in order to significantly change its orbit.

The current consensus is that the Moon was formed by a collision of another planetary body with the Earth that broke off a Moon-sized chunk of the Earth's mass. That impact event did not throw the Earth off its orbit. I do not know the kinetic energy of that impact, but it would have been sufficient to remelt the Earth.

To use a more measurable example, the Chicxulub Crater that is believe to be the result of the impact event that caused the mass extinctions of 65 million years ago was 5e23 joules. That did not knock the earth off its orbit, but it was 1,000 times more energy than annual worldwide energy consumption and 10 times more than world fossil fuel reserves.

So no, no scientists could do this. It would need to be a planetary impact event that would have more than enough energy to melt the earth. Freezing cold is the opposite of the problem you would have.
posted by Tanizaki at 10:32 AM on August 7, 2013 [3 favorites]

Best answer: 1 J in... is equal to...
SI base units 1 kg·m2/s2

Weight of the earth is 5.972E24 kg

So to accelerate the earth at only 1m/s away from its orbit requires 5.972E24 joules. So basically 6 yottajoules. Annual global energy consumption is half a zettajoule (5E20) give or take a few exajoules. So you'd basically need 1,000 times the amount of energy in a year applied in a single direction. So maybe a meteor?

Assume a meteor strikes at about 150m/s. E=mv^2 so solve for m. M is 2.6E20 kg. So something about 1/300th the size of the moon could send the earth out at 1m/s on its orbit. Which probably wouldn't be enough to notice still.
posted by Talez at 10:37 AM on August 7, 2013

Best answer: This sounds like a perfect question for this guy.
posted by pibeandres at 10:47 AM on August 7, 2013 [1 favorite]

Best answer: A closely related question has been addressed by XKCD's What If. Maybe he'd address this one as well if you submitted it.
posted by jeffjon at 10:49 AM on August 7, 2013

Best answer: You might enjoy this thing.
posted by box at 10:53 AM on August 7, 2013

Best answer: I know this may count as a "jokey" answer, but this is basically a major plot point of the first season of Frisky Dingo (spoilers), as Killface wants to push the earth out of its orbit (in the other direction -- into the sun) with his Annihilatrix.
posted by dhens at 11:53 AM on August 7, 2013 [1 favorite]

Best answer: That impact event did not throw the Earth off its orbit.

We don't actually know that. Jupiter contains more mass than all the rest of the solar system combined (not counting the sun) and its gravitational influence controls the shapes of all the orbits of the other planets.

The impacting body that created the Moon began as a collection of mass in one of Earth's trojan points, and eventually grew to be about the size of Mars. When a body is that large, the gravitation trick that holds things in trojan points ceases to work, and the body began to wander. That would have placed in in nearly the same orbit as Earth, so when it eventually came too close and hit the Earth the difference in speed wasn't all that great

But it was somewhat different, and it should have affected the orbit of the combined mass to some extent. However, in the intervening time Earth's orbit would have been regularized again by the gravitational influence of Jupiter.

As to the Dinosaur Killer, its ecological consequences were enormous but the amount of kinetic energy involved, compared to the kinetic energy of Earth in its orbit, was miniscule. There would have been some small change, but again over time Jupiter would have regularized it again.
posted by Chocolate Pickle at 12:14 PM on August 7, 2013

Best answer: If my googled formulas and back of envelope math are correct, accelerating Earth from its current orbit to a circular orbit at the perihelion of Mars's orbit would take 2.4E+55 joules.

Which is a lot of joules. Again applying back of envelope math that's almost certainly at least a few orders of magnitude off, if you used the entire energy output of the sun and magically converted it into into extra kinetic energy of Earth, you still could not move Earth from its orbit to Mars's orbit within the sun's life. Not by a longshot; the numbers I got were that it would take about two billion trillion years.
posted by ROU_Xenophobe at 1:36 PM on August 7, 2013

Best answer: A relevant paper: Korycansky, Laughlin, and Adams. Astronomical engineering: a strategy for modifying planetary orbits. arXiv:astro-ph/0102126. The discussion section, starting on page 17, is fairly accessible, as is this later conference presentation (?) by the first author, and this very nontechnical McSweeney's interview. (The conference presentation also cites prior occurrences of the idea in science fiction.)

They consider gradually enlarging the Earth's orbit by 50% over the next few billion years, using "a Kuiper Belt object or main belt asteroid" to transfer orbital energy from Jupiter to Earth via gravity assist maneuvers. The billion-year timescale is (as far as I understand) only because their purpose is to keep Earth getting the same amount of insolation from the changing sun, not because of any limitation of the method; their plan has one encounter every 6000 years, but I guess you could have an encounter every time the planets are lined up right, which they say happens "every 13 months or so", though doing that would require more objects (or more energy, if you use one object in a smaller orbit than they propose).

In their plan, the change in Earth's orbital energy is on the order of 1040 ergs, and "an optimistic minimum energy expenditure is about 1036 ergs", i.e., 1029 J. See Wikipedia's Orders of magnitude (energy) for some reference points: 1029 J is about 1% of the Sun's daily output, but about a billion years' worth of our current worldwide energy consumption.

So you'd have to suppose your mad scientist had invented some amazing new energy source. Then you'd have to give them a reason not to use the energy more directly to cause havoc; say, you could assume the energy source only works in shallow gravity gradients, so you have to build it far from the sun, like out in the Kuiper Belt. But then you'd have to come up with a reason that the mad scientist wants to threaten us with a slowly changing orbit, when with their assumed capabilities it'd be just as easy for them to make far more conclusive threats, such as sterilizing the planet by arranging a collision with a big Kuiper Belt object...
posted by stebulus at 2:49 PM on August 7, 2013 [1 favorite]

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