the Sun will expand and become a red giant.

And the Earth might be just in the way...

If humans were still around then...

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.

Maybe we could save ourselves some trouble

by moving our whole planet instead.

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.

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 only for 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.

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 be taking 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 here 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 living on those planets that can save them -

at least, not that we know about.

Maybe we'd be better off terraforming another planet to use as our new home.

But that's a story for another WHAT IF.