Habitable zones around parent stars do not always remain at the same distances from the stars.

As the latter evolve over time, the radius of the stars and their overall luminosity also change.

Earth will no longer remain in the habitable zone in around one billion years’ time

Indeed, it is expected that our sun’s habitable zone will also change, moving further out as the sun’s overall luminosity increases with time.

Even before the sun reaches its red giant phase in five billion years’ time, as the sun’s luminosity slowly but inexorably increases, Earth will no longer remain in the habitable zone in around one billion years’ time. This will occur when the sun’s luminosity would have increased by an estimated 10 per cent over its current total luminosity.