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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.

Strikers
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1 Answers1

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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).

Free Consulting
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    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! –  Dec 23 '14 at 08:43
  • 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. – LocalFluff Dec 23 '14 at 11:16
  • @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. –  Dec 23 '14 at 12:58
  • @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. – Free Consulting Dec 23 '14 at 13:11
  • @Evert Oh, a special case ;p Unlike all of the other standard planets, like... ehm. – LocalFluff Dec 23 '14 at 13:19
  • @LocalFluff What's your point? That the definition of HZ with liquid H2O is a bad one? It seems reasonable that planets like Venus can exist but with water. The concept (and zone itself) will be narrowed down as we obtain more details on exo-planets. –  Dec 23 '14 at 13:26
  • "receive an amount of radiative energy to keep H2O in the liquid phase" On the surface. Ice-moons with tidally heated inner seas, like those around Jupiter, need not fall in the Goldilocks zone in order to support life. – Wayfaring Stranger Dec 23 '14 at 16:07
  • @Evert I don't want to be obnoxious on the HZ-issue, I have no better definition myself. But I think that it should be reminded that our nearest two bodies, the Moon and Venus, show us what huge spread is possible even within the habitable zone. And how do they know that they have found any exoplanets at all? Aren't they maybe exo-dwarf-planets according to the new definitions of the IAU? And on that issue I do confess that I am a bit obnoxious, but only because they started it! – LocalFluff Dec 23 '14 at 19:02
  • @LocalFluff, the inner edge of so called "consevative HZ" (0.725AU) lies about Venus's orbit with aphelion in and perihelion out, so it's pretty marginal even without taking greenhouse effect into account (and I'd really like to avoid that, because it extends the outer edge toward ridiculous distance >2AU). – Free Consulting Dec 23 '14 at 20:30
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    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). –  Dec 23 '14 at 20:53
  • @Evert, exactly. Conservative HZ concept is practical for selecting area of interest and doesn't relies on too many assumptions... as while transit method can give us a few information about exoplanet's atmosphere, we have no tools at all for assessing exoplanet's albedo. Meanwhile, I see Titan as highly special case because it orbits near huge cyclotron. – Free Consulting Dec 23 '14 at 21:40