In a billion years, the sun will start to run out of fuel and expand to become a red giant. Earth’s oceans and atmosphere will be burned away, and Earth will likely be engulfed by the sun altogether. The sun will then shrink to a dim white dwarf, and all light and warmth in the solar system will diminish. In a hundred trillion years, the galaxy’s ability to produce stars will be exhausted, and everything will turn dark. However, there’s a way for life to escape this fate—and what’s more, we wouldn’t need to leave the planet to do it. We just need to build some safeguards.

First problem—the sun. To block it out, we can place a large sunshade at the Lagrange point 1 (a gravitational balancing spot between the sun and Earth). We’d need to cover a huge 70-degree area of the sky to ensure the red giant would be eclipsed.

To reduce the required area of our sunshade, we can place a weight at Lagrange point 1, attach a long cable and place the shade close to Earth, just outside the moon’s orbit. We could mine 40% of the dwarf planet Ceres to produce a carbon tether 2 million km (1.2 million miles) long, and 0.01% of the moon to produce an aluminum sunshade 350,000 km (217,000 miles) in radius.