What will happen to us when the Sun turns into a red giant?

Some 5 billion years from now, the Sun will expand and become a red giant. And the Earth might be just in the way… If humans were still around then, would we leave the Earth? Or would we move it?

What is the Sun’s problem anyway? Like any other star, it has an expiration date.

The beginning of its end will feature our Sun swelling into a red giant, wiping out everything that happens to be orbiting it too closely. Like the Earth.

If we wanted to survive, we’d need to take action long before the Sun started going on a rampage. It would take a billion space shuttles to evacuate about 7.5 billion Earthlings.

Even if we could launch 1,000 space shuttles every day, it would take over 2,700 years to move everyone off the doomed planet. After that, we’d spend maybe millions of years finding a new home and terraforming it into a livable place. Maybe we could save ourselves some trouble by evacuating our whole planet instead?

That’s actually quite possible. We’d only need to give the Earth one big boost in the right direction – and keep it on course. And there are a few ways to do that.

Every time we launch a rocket into space, it moves the planet into a slightly different orbit. Lucky for us staying on Earth – and unlucky for the purpose of moving it – this effect is barely noticeable.

To move the planet out of danger, we’d have to change its velocity by 1,200 meters per second (3,937 feet per second). That would require about 7,000 of the most powerful rockets ever built.

But this plan has one big flaw. To escape the Sun’s expanding flames, we’d need to escape pretty far – at least move into the orbit of Mars.

Moving something as bulky as the Earth to a safe zone there might take us billions of years. And for every billion years that passed, we’d use up about a third of the Earth’s mass as propellant. That’s not very efficient, is it?

To move the Earth more efficiently, we’d have to consider electric propulsion. Unlike the chemical one used in most rockets, electric propulsion doesn’t require a lot of mass. We could get away with sacrificing only 2% of the Earth’s mass every billion years. You’d hardly notice the difference.

But this option would require a lot of power – about 800 times more than what’s produced here on Earth right now.
Plus, it would take some careful engineering to make this work.

Because the Earth is spinning, a rocket placed in one location would not always point in the right direction. We’d need to place rockets all around the Earth, and have each of them fire for only a certain amount of time. That would keep the Earth on course.

It would take a billion years to move the planet out of the danger zone. Any miscalculation could mean extinction.

There is a better way. And it involves asteroids.

Aerospace engineers use something called a gravitational slingshot to alter a spacecraft’s path without using too much propellant. When a spacecraft approaches the Earth, and then leaves its gravitational pull, it receives some of the Earth’s orbital energy.

We could use the same effect to redirect our planet. First, we’d have to make comets or asteroids pass close to the Earth, transferring some of their energy in the process.

Next, engineers would redirect the asteroids close to Jupiter and Saturn, where they would pick up some of the gas giants’ energy. From there, the asteroids would bring that energy back to Earth. We’d repeat the process over and over again until it got us to a safe orbit.

Of course, that would be quite dangerous too. The slightest miscount might redirect a gigantic asteroid right into the planet, and destroy all life as we know it.

We wouldn’t take the Moon on our road trip around the Solar System. Most likely, we’d ditch our celestial partner the moment we pushed Earth’s orbit away from the Sun.

The big risk is that moving Earth might disrupt the whole planetary system. It could easily destabilize Mercury or Venus, setting them on the path of destruction. And there is no one there to save those planets – at least, not that we know about.

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