When the Sun expands into a red giant about 5 billion years from now, the Earth will be dragged into its atmosphere.

Three astronomers suggest moving Earth to the orbit of Mars, allowing Earth to receive about as much sunlight as it receives today. That could be accomplished by changing the orbits of icy bodies in the distant solar system so they would pass close to the Earth, transferring some of their orbital energy to the planet.

Another possibility: a free-floating solar sail, 19.2 times the Earth’s diameter, at a point beyond the Moon where the pressure of solar radiation essentially balances the Earth’s gravitational pull, increasing the Earth’s orbital energy and accelerating the center of mass of the system outwards, away from the Sun.