User:Marskell/Planetary Habitability

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Planetary habitability is the measure of an astronomical body's potential for developing and sustaining life. It may be applied both to planets and to the natural satellites of planets.

The only absolute requirement for life is an energy source (usually but not necessarily sunlight), but the notion of planetary habitability implies that many other geophysical, geochemical, and astrophysical criteria must be met before an astronomical body is able to support life. Given that the existence of life beyond Earth is currently unknown, planetary habitability is largely an extrapolation of Earth's conditions and the characteristics of the Sun and solar system which appear particularly favourable to life's flourishing.

The idea that planets beyond Earth might host life is an ancient one, though historically it was framed by philosophy as much as physical science 1. The late 20th century saw two breakthroughs in the field. The observation and robotic exploration of other planets and moons within the solar system has provided critical information on defining habitability criteria and allowed for geophysical comparisons between the Earth and other bodies. The discovery of extra-solar planets—beginning in 1995 and accelerating thereafter—was the second milestone. It confirmed that our sun is not unique in hosting planets and expanded the habitability research horizon beyond our own solar system.