 Circumstellar habitable zone

A circumstellar habitable zone is an orbital region in which a specified planetary and atmospheric model can maintain surface liquid water. A simple radiative scaling gives distance $a\propto \sqrt{L_{\star }/S_{\mathrm{eff}}}$, where $L_{\star }$ is stellar luminosity and $S_{\mathrm{eff}}$ the incident irradiance at a chosen climate boundary. The required irradiance depends on the stellar spectrum and atmospheric opacity.

Model inner limits involve water loss or a runaway greenhouse; a maximum greenhouse outer habitable-zone limit is a common outer criterion. Published one-dimensional estimates explicitly depend on water and carbon dioxide absorption and on their treatment of clouds.^[ref] The zone is therefore a conditional climate calculation, rather than a guarantee that each planet within it is habitable.

The circumstellar habitable zone (CHZ), often referred to as the "Goldilocks Zone," is the region around a star where conditions might be just right for liquid water to exist on the surface of a planet. This zone is critical for the potential habitability of planets, as liquid water is a key ingredient for life as we know it.