Habitable Zone for a Planet

Around a given star, there will be a habitable zone where the temperatures will be in a range that could support advanced life. The advanced life that we know about depends upon water, so one condition for the habitable zone is that water can exist in liquid form, so this requires a temperature range between 0°C and 100°C. That's a fairly narrow range, but this question about the habitable zone has been studied extensively, and the real required range is more like 5°C to 40°C.

Distance From a Star

To be in the habitable zone around a star a planet's orbit needs to be nearly circular and be at a distance where all three phases of water can be present on the surface of the planet.

Calculations in 1978 by Hart indicated runaway glaciation if the Earth were 1% further from the Sun and runaway greenhouse effect if it were 5% closer to the Sun. Kasting in 1993 included an additional regulatory influence called the CO₂-silicate cycle, and projected a CHZ (continuously habitable zone) of 0.95 - 1.15 AU.

A Stable Planetary Orbit is Needed for Advanced Life

To be in the habitable zone around a star a planet's orbit needs to be nearly circular and be at a distance where all three phases of water can be present on the surface of the planet.