Habitable Zone Evolution

Habitable zones are not static — they migrate outward as stars age and brighten. Earth has been in the Sun's habitable zone for 4.5 billion years, but the zone's inner edge has been creeping outward. In roughly 1 billion years, the Sun will be bright enough that Earth's oceans will begin to evaporate, ending surface habitability.

As the Sun brightens, the whole zone drifts outward, so Mars will move from the cold outer edge toward the warmer middle. Even then, its thin atmosphere and missing magnetic field would likely keep surface liquid water out of reach. Tracking how habitable zones evolve over a star's lifetime is key to estimating how long a planet can support life.