The Goldilocks Zone

The habitable zone (HZ) is the orbital band around a star where temperatures allow liquid water on a planet's surface — not too hot, not too cold. For the Sun, this zone extends from roughly 0.95 to 1.67 AU (astronomical units). Earth sits comfortably inside. Venus orbits just inside the hot inner boundary, while Mars sits out at the cold outer edge.

The habitable zone shifts depending on the star. Red dwarfs, which are cooler and dimmer, have habitable zones much closer in — sometimes as close as 0.1 AU. That closeness brings problems: a planet that near tends to become tidally locked, keeping one face toward the star forever, and it sits in the path of powerful stellar flares that can strip away its atmosphere.