<p>From your first link, the definition is:</p>

<blockquote>
  <p>"The circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.[1][2][3][4][5] The bounds of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun."</p>
</blockquote>

<p>but as you will see further down in that same article:</p>

<blockquote>
  <p>"In subsequent decades, the CHZ concept began to be challenged as a primary criterion for life, so <strong>the concept is still evolving</strong>. Since the discovery of evidence for extraterrestrial liquid water, substantial quantities of it are now thought to occur outside the circumstellar habitable zone. The concept of deep biospheres, like Earth's, that exist independently of stellar energy, are <strong>now generally accepted</strong> in astrobiology given the large amount of liquid water known to exist within in lithospheres and asthenospheres of the Solar System. Sustained by other energy sources, such as tidal heating or radioactive decay or pressurized by non-atmospheric means, <strong>liquid water may be found even on rogue planets</strong>, or their moons."</p>
</blockquote>

<p>So really, it's just historical - it is accepted now that it is a limited view, and there is just as likely to be liquid water elsewhere. That doesn't necessarily mean life is as likely, as with lower solar radiation, there may be insufficient energy to support life even with liquid water.</p>

CC BY-SA 4.0
2019-02-14T20:27:55.627Z
2019-02-14T20:27:55.627Z
Rory Alsop
<p>According to <a href="https://en.wikipedia.org/wiki/Circumstellar_habitable_zone" rel="nofollow noreferrer">Circumstellar habitable zone</a></p>

<blockquote>
  <p>In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure</p>
</blockquote>

<p>But then you have moons in the solar system such as Titan, Europe, Enceladus where some scientists believe life could be possible. </p>

<p><a href="https://www.theguardian.com/science/2018/jun/17/the-most-likely-cradles-for-life-our-solar-system-mars" rel="nofollow noreferrer">The most likely cradles for life inside our solar system</a></p>

<p><a href="https://en.wikipedia.org/wiki/Life_on_Titan" rel="nofollow noreferrer">Life on Titan</a></p>

<p>Why the CHZ is defined as it is, if life could be possible outside of it? Is it pourly defined or scientists believing there could be life outside the CHZ in the solar system are having too much wishful thinking?</p>

<solar-system><habitable-zone><titan><europa><enceladus>
Why the Circumstellar Habitable Zone is defined as it is, if life could be possible outside of it?
Pablo
# Why the Circumstellar Habitable Zone is defined as it is, if life could be possible outside of it?

(Asked by: username_0 on 2019-02-14)

According to [Circumstellar habitable zone](https://en.wikipedia.org/wiki/Circumstellar_habitable_zone)

> In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure

But then you have moons in the solar system such as Titan, Europe, Enceladus where some scientists believe life could be possible.

[The most likely cradles for life inside our solar system](https://www.theguardian.com/science/2018/jun/17/the-most-likely-cradles-for-life-our-solar-system-mars)

[Life on Titan](https://en.wikipedia.org/wiki/Life_on_Titan)

Why the CHZ is defined as it is, if life could be possible outside of it? Is it pourly defined or scientists believing there could be life outside the CHZ in the solar system are having too much wishful thinking?

**Tags:** solar-system, habitable-zone, titan, europa, enceladus


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## 1 answers

### Answer by username_1 on 2019-02-14. Score: 9 | Accepted answer

From your first link, the definition is:

> "The circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.[1][2][3][4][5] The bounds of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun."

but as you will see further down in that same article:

> "In subsequent decades, the CHZ concept began to be challenged as a primary criterion for life, so **the concept is still evolving**. Since the discovery of evidence for extraterrestrial liquid water, substantial quantities of it are now thought to occur outside the circumstellar habitable zone. The concept of deep biospheres, like Earth's, that exist independently of stellar energy, are **now generally accepted** in astrobiology given the large amount of liquid water known to exist within in lithospheres and asthenospheres of the Solar System. Sustained by other energy sources, such as tidal heating or radioactive decay or pressurized by non-atmospheric means, **liquid water may be found even on rogue planets**, or their moons."

So really, it's just historical - it is accepted now that it is a limited view, and there is just as likely to be liquid water elsewhere. That doesn't necessarily mean life is as likely, as with lower solar radiation, there may be insufficient energy to support life even with liquid water.


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