Description: The habitable zone of a star is defined as the region around it where liquid water can exist on the surface of an Earth-like planet. If Earth were much farther away from the Sun, all surface water would freeze; much closer, and all surface water would boil off. In neither case could life as we know it form or survive. Sometimes, the habitable zone concept is extended to include a planet like Venus, with its runaway greenhouse effect, where liquid water could exist even if the planet were farther away from the Sun. The galactic habitable zone is that part of our Galaxy where conditions are suitable for life-bearing planetary systems: there, heavier elements, which Earth-like planets are made of, should be sufficiently common, and life-threatening events like supernovae sufficiently rare.

It should be noted that habitable conditions may exist outside of the habitable zone. For example the possibly habitable subsurface ocean on Jupiter's moon Europa.

Related Terms:

• Astrobiology
• Extraterrestrial Life
• Greenhouse Effect
• Supernova
• Planetary System

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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