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By Dr. Hugh Ross
For life to be possible on a planet, the planet must simultaneously reside in all the known habitable zones. So far, astronomers have identified nine distinct habitable zones. I described eight of these zones in my book Improbable Planet.1 The ninth, the electric field habitable zone, was discovered just several months ago.
The two habitable zones that have been the subject of the most research by astronomers are the liquid water habitable zone and the ultraviolet habitable zone. All physical life-forms need liquid water to exist. The liquid water habitable zone marks where liquid water conceivably could exist on a planet, depending on its distance from a star.
Ultraviolet radiation is needed for the synthesis of many biochemical compounds that are essential for physical life. Therefore, if the ultraviolet radiation from a host star is too weak, no life is possible on that planet. On the other hand, if the ultraviolet radiation falling upon a planet’s surface is too strong, DNA and other life-critical biomolecules will be damaged to a degree that wipes out all life. The ultraviolet habitable zone is the area where the ultraviolet radiation from a star is neither too weak nor too strong for the existence of life.
Other astronomical sources of ultraviolet radiation besides the host star can complicate the ultraviolet habitable zone. Such possible sources include…
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