Title: Planetary habitability - Wikipedia
Headings: Planetary habitability
Planetary habitability
Contents
Earth habitability comparison
Suitable star systems
Spectral class
A stable habitable zone
Low stellar variation
High metallicity
Planetary characteristics
Mass
Radius
Orbit and rotation
Geology
Geochemistry
Microenvironments and extremophiles
Ecological factors
Alternative star systems
Binary systems
Red dwarf systems
Size
Other factors limiting habitability
Longevity and ubiquity
Massive stars
Four classes of habitable planets based on water
The galactic neighborhood
Other considerations
Alternative biochemistries
"Good Jupiters"
Life's impact on habitability
The role of chance
See also
Notes
References
Bibliography
Further reading
External links

Content: Planetary habitability - Wikipedia
Planetary habitability
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"Habitable planet" redirects here. For a list of potentially habitable planets found to date, see List of potentially habitable exoplanets. Extent to which a planet is suitable for life as we know it
Understanding planetary habitability is partly an extrapolation of the conditions on Earth, as this is the only planet known to support life. Planetary habitability is the measure of a planet 's or a natural satellite 's potential to develop and maintain environments hospitable to life. Life may be generated directly on a planet or satellite endogenously or be transferred to it from another body, through a hypothetical process known as panspermia. Environments do not need to contain life to be considered habitable nor are accepted habitable zones the only areas in which life might arise. As the existence of life beyond Earth is unknown, planetary habitability is largely an extrapolation of conditions on Earth and the characteristics of the Sun and Solar System which appear favorable to life's flourishing. Of particular interest are those factors that have sustained complex, multicellular organisms on Earth and not just simpler, unicellular creatures. Research and theory in this regard is a component of a number of natural sciences, such as astronomy, planetary science and the emerging discipline of astrobiology . An absolute requirement for life is an energy source, and the notion of planetary habitability implies that many other geophysical, geochemical, and astrophysical criteria must be met before an astronomical body can support life.