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I've a question on Habitable zone.

Does Habitable zone represent the region where we humans or the living beings of earth can survive?

Or is it a region where life can exist?

If it is second I want to know what are the parameters that are considered for existing of life.

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Nothing that complex. Habitable zone merely defined a circumstellar volume where a planet (if any) can receive an amount of radiative energy to keep H2O in the liquid phase.

Yes, it has been based on the requirements for life from Earth, lacking any wider samples.

I encourage you to play around with interactive illustration of concept (Flash applet).

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    $\begingroup$ Hi and welcome to the site, this is a nice concise answer. Do you have any sources you could perhaps add to back up your definition? Thanks in advance! $\endgroup$ – RhysW Dec 23 '14 at 8:43
  • $\begingroup$ But it is dependent on assumptions about the atmosphere, isn't it? There's no liquid water on the Moon, which is as much in an HZ as Earth is. And Venus completely lacks water, it seems to be the very driest of all planets. $\endgroup$ – LocalFluff Dec 23 '14 at 11:16
  • $\begingroup$ @LocalFluff Its definition does include the capability of the planet to have enough mass to hold liquid water through its atmospheric pressure. I guess Venus is somewhat special case in that the atmospheric contents caused such a greenhouse effect that there is no liquid water to be found anymore, but a different starting atmosphere could have led to different current atmosphere, with liquid water. $\endgroup$ – user51 Dec 23 '14 at 12:58
  • $\begingroup$ @RhysW, if there is a demand for the complex answer, I could add an another post, but it will be a very vague one since there are numerous studies and numerous assumptions about HZ which (IMO) reduces a confidence in the whole concept. $\endgroup$ – Free Consulting Dec 23 '14 at 13:11
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    $\begingroup$ I just tend to accept it as a workable definition for now, which will presumably sharpened as insights progress. The intention is clear enough, and I don't expect its definition will limit any searches for life elsewhere (e.g. Titan). $\endgroup$ – user51 Dec 23 '14 at 20:53

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