Astronomers may have found a way for humans to survive when the sun dies.

Humans will have to find a habitable planet with a neighboring planet that can produce tidal heat.

Tidal heat refers to the frictional push and pull of a planet and its neighboring planet on one another.

Rory Barnes, an astronomer for University of Washington, said this phenomenon can happen to exoplanets, or planets in another solar system.

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Researchers found out that the gravitational pull of an outer planet could generate enough heat to prevent internal cooling in a planet the size of Earth, further extending a planet's ability to support life.

Barnes explained that when planets are closer to a star, the gravitational field is stronger and the planet turns into a shape of an American football.

He added that if the star is farther from the planet, the field weakens and the planet relaxes into a more spherical shape.

The constant flexing causes the planet's layers to rub against each other causing frictional heat, he said.

Barnes said an outer planet is necessary to keep the orbit of a potentially habitable planet noncircular.

He explained that when a planet's orbit is circular, the gravitational pull from its host star remains constant causing its shape to remain the same and eventually stopping the tidal heat.

Researchers suggest that future discoveries of Earth-sized planets should be preceded by a search for outer planets that might improve another planet's ability to host life.

They said the combined effect of a planet's own tectonics and tidal heat generated by an outer planet can allow the planet to host some of the longest-lived surface habitats in the universe.