In half a billion years, the sun will swell up like a blowfish and cause the Earth to become a parched moonscape, devoid of all but microbial life. But don't worry about it. Scientists have a plan for moving the Earth to a more habitable zone. And all it'll take is ten million years.

Moving the Earth may be the only way to save humanity, once the sun's outer layers expand. If the Earth doesn't get out of the way, its water and atmosphere will boil away into space, and then our planet will fall into the sun itself. That's not going to work for us — so sometime before then, if we want to keep using the Earth as a home base, we're going to have to move it back a bit. Working from the theory that you should never put off for a billion years what you can do today, scientists came up with a plan.


The good news is that the principle behind this plan has not only existed but been in use since the 1970s. It's called a gravity assist, and we've been using it to get satellites to change their trajectory, and speed up or slow down, since then. The first major use was when Voyager 2 got a boost from Jupiter to get to Saturn, then got an assist from Saturn and Uranus to make its way outward. This principle has been used to slow down satellites — Galileo was slowed down by Io so it could pass by Jupiter — and to get satellites that have mistakes in trajectory, like a geosynchronous satellite that didn't quite sync up, to the right speed and position. Gravity assists provide maximum bang for the buck, and can get satellites going at speeds far greater than any actual fuel could.


The idea is simple. Get a satellite close to a planet and the planet's gravity will grab hold of it. If the satellite is heading straight towards a planet, it will just fall right into the planet and go splat on the ground. (Or whoosh through the gas, or sizzle near the center, or crack on the ice, depending on the planet in question.) If it's moving at an angle to the planet, though it'll still get pulled by gravity, which will add to its momentum — but it'll fall around the curve of the planet, and escape back into space. It would be a little like grabbing hold of a friend as they ran by you. You might be able to pull them towards you, changing their direction and even speeding them up, but then they'd tear free and speed away from you again.

Since the satellite is gaining new direction and more momentum, the planet is also changing direction and momentum. Since the planet is so much bigger than the satellite, we won't much notice the planet's change. The plan is to increase the size of the satellite, to rope in a big asteroid, and sling it around the Earth. The asteroid would be the size of Long Island and have solar powered rockets. The asteroid's nearby flight will cause the Earth to change momentum, tugging it away from the sun and out of the danger zone.


The bad news is this is neither a fast nor an easy process. It would have to be repeated no less than six thousand times. Some estimates say it could take up to a million times. In between passes, the asteroid would have to go to Jupiter or Saturn, which would gravity-assist the asteroid back to Earth. Each pass would take the asteroid between 16,000 and 10,000 miles away from the Earth. Any mistake would either lose the asteroid, or would cause the asteroid to hit Earth, killing every single thing on it, with the possible exception of microbes. Still, compared to a fall into the sun, it's gotta be the best option, right?


Not if you live on the coast. The asteroid's pull on the tides would be ten times the pull of the Moon. It would cause storms, tsunamis, and chaotic seasonal changes. We'd also have to calculate its passes, so it wouldn't change the rotation of the Earth and give us, say, a twenty-three-hour day. Even if we did move the Earth, ideally to about where Mars is right now, we'd have a different orbit around the sun, and we'd have Mars as a freaky new neighbor, which might also play hell with our own orbit. What's the possible up side? Another five billion years of habitability on Earth. Right now, it looks like we might have, at the outside, about three billion — with things getting bad at the half a billion mark. I don't know about you, but five billion more years on Earth seems like it would be worth, say, forty million years' work. Who wants to get started on those solar powered rockets?

Top Image: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

Galileo Image: NASA

Asteroid Image: NASA/JHUAPL

Via NASA twice, CNN, and How it Ends.


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