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: 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. In its astrobiology roadmap, NASA has defined the principal habitability criteria as "extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism ". In August 2018, researchers reported that water worlds could support life. Habitability indicators and biosignatures must be interpreted within a planetary and environmental context. In determining the habitability potential of a body, studies focus on its bulk composition, orbital properties, atmosphere, and potential chemical interactions. Stellar characteristics of importance include mass and luminosity, stable variability, and high metallicity.