So I was reading this article recently, titled Stellar Outburst Brings Water Snow Line into View: http://www.eso.org/public/news/eso1626. In short it's about a protoplanetary accretion disc around a young star. The closer the disc is to the star the hotter it gets. But on the farther side of the disc it can get cold enough for water/snow to collect. See the article for details.

First of all, holy wow! Secondly, that gave me an idea for something similar to Larry Niven's Smoke Ring from his Integral Trees books.

There must be an area in the accretion disc where the water/snow line is warm enough for the water to remain liquid, just between too hot and too cold. I know I'm stretching here and it would take all kinds of handwave. The speed the disc is spinning at is probably too great to allow for it; The disc itself is probably too turbulent; All the stuff in it probably mixes up chaotically; It all gets pulled into the star; Radiation, etc. etc.

But in the article it reads that the outer edge of the disc (the water/snow line) was as far away from its star as Pluto is from our sun. At that distance maybe the conditions of all that turbulence are lessened. Move that area in closer to the star, say to the goldilocks zone, and you might get a water/snow "zone/ring" that is warm enough and stable enough for the conditions I'm looking for.

Could that band be large enough that creatures who could breathe water could live and swim around in it?

Sub question: What with all that stuff in the disc being the matter that later creates life could life originate in that area?

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  • $\begingroup$ Len I think you may need to focus your question down a bit. Can you provide a proposal and ask either, "what am I missing" or "why won't this work?" $\endgroup$
    – James
    Commented Mar 29, 2018 at 19:46
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    $\begingroup$ @James, I gave it a shot. I hope that helps. If not please let me know what you have in mind. Thanks! $\endgroup$
    – Len
    Commented Mar 29, 2018 at 20:00
  • $\begingroup$ Larry NIven's books Smoke Ring and Integral Tree are about this is I am not mistaken. $\endgroup$
    – John
    Commented Jun 29, 2018 at 13:47

3 Answers 3


I'm going to science this question up, with graphics and links to research!

This is the phase diagram for water.

Phase diagram for water

As you can see, it takes pressure for water to be a proper liquid. In a vacuum, it goes straight from solid to gas and vice-versa.

It would take approximately 0.6% atmospheres to allow for liquid water. As low as that seems, it is still much more than what you would get in space.

But don't give up just yet!

Interstellar Ice Acts Like a Liquid in Ultraviolet Light

When exposed to ultraviolet light, interstellar ice may act more like a liquid than a solid, a new study has found.

Researchers discovered this effect while re-creating the conditions of our early solar system's planet-forming disk in a laboratory environment, revealing how organic chemistry might react to the deep freeze of the system's outer regions and how the seeds of planets accumulate material.

And what is the biggest UV source in our solar system? Why, the sun itself!

Any lifeforms developing in your environment would probably be slow compared to us. But that's just a detail. The important thing is that life always finds a way.


No, this isn't realistic.

I'm considering the same issues for a D&D outer-plane-of-elemental-air campaign setting. Luckily, fantasy is made of handwavium.

In real life, the problems won't just be temperature - to begin with, you're talking about two very different kinds of pressure.

Consider that at the top of Mount Everest, the air pressure is low enough for water to boil at 71 degrees Celsius. A proto-planetary disk is still very close to a vacuum relative to our atmosphere, so even if it's warm enough for humans - say, 25 degrees Celsius - any liquid water is still going to boil off into vapor. And by "liquid water," I'm also including blood. Without a pressurized environment, the gasses that are soluble in blood will boil off first, giving you the bends, followed by your plasma.

Then there's the pressure the star is exerting on the disk. Light and radioactive solar flares will actually blow gases away from the star itself, toward the too-cold region.

Speaking of radioactivity, you'd have to construct a magnetic shield to keep human-based lifeforms alive. I remember The Integral Trees had the rocky core of a gas giant; if it generates enough magnetism, you might be able to construct some kind of space station around that?

But yeah, this requires lots of hand-waving, as you said.

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    $\begingroup$ As Darth Vader said: "NOOOOOOOO!!!" Alright, I give up. $\endgroup$
    – Len
    Commented Mar 29, 2018 at 20:59
  • $\begingroup$ Couldn't water itself serve as an effective shield against radiation? $\endgroup$ Commented Mar 29, 2018 at 23:52
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    $\begingroup$ If it was a container of liquid water, yes. In fact, liquid heavy water is one of the things used to contain nuclear wastes here on Earth. However, in this case, we're talking about water vapor dispersed in a vacuum. That's not going to be enough to protect most lifeforms. $\endgroup$ Commented Mar 30, 2018 at 2:52

Just a quick note that it's important to realize that there is no liquid water in a protoplanetary disk because the pressure is too low. There's just water vapor where it's hotter than about 150 K (a little colder than -100 degrees Celsius), and ice where it's colder than that.

No liquid anywhere I'm afraid.

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    $\begingroup$ As Darth Vader said: "NOOOOOOOO!!!" Seriously though, not even allowing for hand wavium? $\endgroup$
    – Len
    Commented Mar 29, 2018 at 20:57
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    $\begingroup$ @Len Fundamental physics I'm afraid. As pressure drops the melting and evaporation points move closer and closer together until eventually it starts sublimating directly from solid to gas and you never get a liquid phase. You need something to create pressure. $\endgroup$
    – Tim B
    Commented Mar 29, 2018 at 21:21

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