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The title is fairly self explanatory. A pocket inside a comet, able to have liquid water and similar pressures to earth. I want a realistic and science based way to achieve this.

requirements:

  • Must have liquid water
  • Must have light for photosynthesis
  • Must reoccur every orbit, if possible it can stay even at the aphelion, but that isn’t required.
  • It must be internal, not on the surface.

Things up to you

  • Any type of star is fine
  • Orbital parameters can be whatever, but they must still be reasonably a comet.
  • The chemical makeup can be anything, but it must contain at minimum all basic parts of life.
  • It can be caused by any method, as long as it happens repeatedly, and is non artificial. It does not have to be likely in any individual comet though.

When answering this question you should evaluate the possibility of the described conditions being met. Any parameters not specified can be assumed to be changed.

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  • $\begingroup$ Natural or artificial? Natural is difficult, because the required heat source will eventually melt the comet. Also, there aren't any natural heat/light sources that fit the bill. Artificial is practical with a fusion reactor, but you'll also need refrigeration to keep from melting the comet. $\endgroup$ Nov 7 at 19:24
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    $\begingroup$ Please edit that into the question, since it's an important limitation on answers. $\endgroup$ Nov 7 at 19:29
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    $\begingroup$ You're being very obstinate. I told you what a google search produced and yet you still think it's an obvious term. Put those big boy pants on and edit your post to clarify a non-standard term. $\endgroup$
    – JBH
    Nov 7 at 19:46
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    $\begingroup$ Yes, STP is a common abbreviation for standard temperature and pressure, if one is a chemist. It is also a common abbreviation for shielded twisted pair or Spanning Tree Protocol, if one is a network engineer. It is also a semi-well-known brand of motor oil, an abbreviation for sodium triphosphate, and many others. This is a common problem with TLAs... $\endgroup$
    – AlexP
    Nov 7 at 19:51
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    $\begingroup$ Oh good grief. You deserve what happened here. $\endgroup$
    – JBH
    Nov 8 at 0:47

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There is reason to believe that large enough comets may contain liquid under their ice shell -- in that a large enough comet becomes a Kuiper belt object like Pluto, Eris, or Haumea, any of which could have acquired a molten layer and, via various mechanisms, retained such a region for a geologically long time (a billion years or so?).

Initial heating can come from accretion energy -- that is, the small "snowflakes" and dust particles impacting on the comet as it forms over a period of eons will each contribute energy that can only be lost by radiation from the surface of the composite body. Later, radioactivity of the denser material at the core will contribute and can lead to the heat persisting for millions of years (there is a current hypothesis that Ceres may still have a molten salt water layer like Europa's subsurface ocean, and it's been proposed that Pluto might as well -- the insulating power of kilometers of anything shouldn't be underestimated).

If such a sub-ocean does form, however, there won't be any light inside and nowhere will the pressure be as low as "Standard Temperature and Pressure" -- not with kilometers of ice on top, even under less than 1% gravity. Therefore such a pocket would have to be artificial, and as such can be anything your worldbuilding heart desires.

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