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The extremes of potential cryofluids
Nafnlaus
post Jul 18 2015, 09:35 AM
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Our solar system has done much to show us that water and silicate magmas are not the only things that can flow on a planet and shape its surface. Io sees flows of liquid sulfur among its silicate flows. Titan, methane and other hydrocarbons. Even places where water has been found to be sculpting the landscapes it's often quite different - for example, enceladus's geysers erupt "seawater" as basic as household ammonia. And for Pluto, scientists have been speculating about bodies of neon and eutectics of nitrogen:

http://www.planetary.org/blogs/emily-lakda.../2011/3182.html

(Although, as the link notes, they couldn't exist fully exposed to the surface, as the pressure is too low).

I started thinking, how extreme could this potentially go?

We really don't know how cold planets / dwarf planets cam get. as we have limits to how far out we can detect these sized bodies. 2012 VP113 has the highest known perihelion at about 80 AU, although Sedna is close at around 76 AU. Objects around this range have the potential for liquid hydrogen on / near the surface (requires 7kPa pressure to hit the triple point). But how much further out can they be without us seeing them? Long period comets, after all, have apohelions as high as 70000 years. It seems quite natural to expect that there would be numerous objects much further out from the sun - or even in interstellar space - which could thus reach very cold temperatures, perhaps even close to thie cosmic microwave background. This is cold enough to condense liquid helium - which can exist on the surface without any pressure at all.

But can we go more exotic?

The cosmic microwave background temperature is 2.72548K, tantalizingly close to helium-4's lambda point of 2.172K. How do we get 4He down to its lambda point? Often by evaporative cooling - a process that most definitely can occur in nature, with the caveat that the gas lost has to be actually *lost* (such as taken away by the solar wind, captured into the gravity of a mutually tidally locked companion, escaping without external help, or whatnot) in order to keep the pressure down to allow it to continue. Evaporative cooling, with perfect removal of the gas, can reach down to about 1,3K, well below the lambda point.

The problem is, my first thoughts were that no realistic gas loss rate from such a body could manage to overcome radiative exchange with the cosmic microwave background, except possibly in very deep, very well insulated situations (where the pressure would probably be too high). But then I started thinking about it more. The smaller the body, the easier it becomes in all respects - less surface area, less gravity to hold onto the gas, etc. And radiative exchange at cosmic microwave background temperatures is extremely slow. Could it be possible?

A Charon-sized body has about 4 million square kilometers surface area, so let's consider a 1 million square kilometer body, cold and dead with no relevant geothermal heating and far enough from the sun that it seems nothing more than a bright star. Let's consider a radiative heat loss rate that needs to be achieved of 5uW/mē (the cosmic microwave background exchanging with lambda point helium would on its own require only 1.8uW/mē with perfect emissivity - in the real world with lower emissivity, less, potentially significantly less). We're assuming no insulating ground cover. Helium has a latent heat of vaporization of 20.754 kJ/kg. This means that the body would only need to lose about 240 kilograms of helium per second. Now, obviously such a body wouldn't be exposed to Pluto-intensity solar wind, or anything close to it. But Pluto (which loses 500 tonnes/s of its atmosphere to the solar wind) also is losing nitrogen, a much heavier gas, and has far more gravity than the thought experiment body described above. And there's other methods to lose gas apart from the solar wind - in short, I could envision such a rate of helium loss in some scenarios. And one can both decrease the required rate of helium loss and the rate of radiative exchange simply by reducing the size of the body in question.

In short, if such a situation were to exist, the helium on the surface could theoretically hit its lambda point and exist as superfluid oceans. And that's something really crazy to envision because superfluids have all sorts of bizarre behaviors.

* Flow with zero viscosity.
* Usually exists as both a fluid and superfluid component mixed together - but the superfluid moves straight through the fluid component without resistance.
* Heat is distributed extremely rapidly throughout the entire body, and (in part) flows in waves like sound.
* Bodies of superfluid at higher elevation tend to rapidly drain themselves over the edges of their contours into lower bodies in a powerful film-flow siphon effect.
* Superfluids can leak through incredibly tiny holes, and do so at incredible speeds - micron-scale holes and dozens to hundreds of meters per second velocity in a "beam" of tiny droplets that act as quantum solvents.
* Application of tiny amounts of heat can cause a powerful fountain effect
* Rotating superfluids contain an array of evenly distributed rotating vortices (rather than rotating as a whole). These vortices exist only in quantized energy states and are arranged in patterns to evenly distribute themselves.
* Waves have extremely low dissipation and seem to be very prone to "rogue waves".

It's hard to picture a world with weirder surface properties than that wink.gif
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Daniele_bianchin...
post Jul 18 2015, 11:43 AM
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extremely extremely interesting. I am very fascinated by super fluids different from water..
You can assume dimensions and pressures for these possible Exotic worlds? or planet size does not affect?
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Nafnlaus
post Jul 18 2015, 11:55 AM
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QUOTE (Daniele_bianchino_Italy @ Jul 18 2015, 11:43 AM) *
extremely extremely interesting. I am very fascinated by super fluids different from water..
You can assume dimensions and pressures for these possible Exotic worlds? or planet size does not affect?


No pressure is required for superfluid helium to form. In a vacuum it'll drop to around 1,3K wherein the vapor pressure reduces to near irrelevance.

The size of the above body is arbitrarily chosen. It does affect things in terms of the amount of area exchanging heat with the cosmic microwave background. When you're not dealing with a small body then internal heating becomes more of a problem. The key aspects for the above to work out are "little stellar, tidal, or internal energy input" and "evaporated helium managing to escape or be captured by another body, to allow the evaporative cooling to continue". The exact details beyond this are not particularly important, but those conditions must be met.
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Nafnlaus
post Jul 18 2015, 05:00 PM
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There are all sorts of other crazy possibilities out there. For example, what can happen with radium and thorium in different circumstances. For example, there can exist natural nuclear reactors. Earth had 16 of them in Oklo, Gabon, when groundwater seeped into a rich uranium deposit 1,7 billion years ago. That can't happen any more, mind you, because natural uranium's U235 concentration has dropped too low for ordinary water to work as a moderator. Heavy water can, but while it's naturally enriched in some places in the solar system, it's doubtful you'd ever find it *that* enriched. But there is another workable moderator that's incredibly abundant: helium. Helium actually has *zero* neutron loss in moderation, it's incredibly efficient. So on a world with helium seas, if a steady supply seeped into a uranium deposit, it could really kick things off. You might even kick off some neat things with significantly radioactive liquids or gases reaching the surface (more in just a second).

Another possibility is a world with subterranean sulfuric acid - which isn't at all unrealistic, we've already found a world with a super-basic ocean (enceladus), why not acidic? Uranium is soluble in sulfuric acid. Radium isn't. So migrating fluids could strongly concentrate radium. Radium at the surface - or probably easier, radon compounds reaching the surface - again gives you the potential for concentrations of significantly radioactive liquids/gases on the surface in places. Gases bubbling out of dissolved uranium without any particular radium concentration could also get to the surface much easier than having to travel through solid rock.

What's neat about strongly radioactive gases or liquids on the surface of a cold world? Well, let's look for a second at what would happen on a cold world with radon snow/frost.

Radon has a freezing point of 202K at 1atm - not super cold, but it would at least have to be colder than Mars. Picture a body with high radon emissions per unit area and an atmospheric temperature below the freezing point of radon. After emission, one might encounter radon snow, radon rime around vents, or other such features - possibly even (diluted) liquid in the right conditions. Liquid and solid radon have an intense radioluminescent glow. Any area that deposited in even small amounts of liquid or solid radon ice or snow would glow in the dark. Liquid radon ranges in glow color from blue-green to lilac. Solid radon changes color with time, starting out blue, then yellow, then orangish-red:

https://books.google.is/books?id=T0Iiv0BJ1E...p;q&f=false

So not only would the whole landscape be lit up, but it would be lit up with different colors based on when the material was precipitated out. And it would look different every day as the radon decayed. If there was an atmosphere (such as nitrogen), it could form glowing clouds (droplets, ice crystals) that likewise change color with time. Streams of different ages would mix together in a blending of rainbow glows. The ultimate fate of any ices and liquids would be to plate out as shiny metallic lead at the end of their decay chains.
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lollipop
post Jul 18 2015, 07:47 PM
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So Pluto sheds 500 tonnes of nitrogen per hour driven by the solar wind. This means that Charon's gravitational potential energy is reduced. Because the gravitational potential energy plus orbital kinetic energy must equal zero, Charon will move outwards and orbit more slowly, tending to break the double tidal lock. Of course tidal friction will act to restore the rotation speeds to match the orbital speed. This is a mechanism whereby solar wind energy can be delivered under the crust of both bodies.
On the back of an envelope I estimate that the orbital energy lost per kilo of nitrogen stripped out is about 200KJ, almost exactly the amount needed to liquify and vaporise a kilo of nitrogen ice. Et voila, a self sustaining process.
I might have this back to front, and there may be overwhelmingly larger effects that I haven't thought about yet...
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nprev
post Jul 18 2015, 07:54 PM
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MOD NOTE: Topic moved out of Pluto section since it is not specific to Pluto nor to a current or planned mission and generally out of scope for UMSF.


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Doug M.
post Jul 20 2015, 04:54 PM
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QUOTE (Nafnlaus @ Jul 18 2015, 07:00 PM) *
So not only would the whole landscape be lit up, but it would be lit up with different colors based on when the material was precipitated out. And it would look different every day as the radon decayed. If there was an atmosphere (such as nitrogen), it could form glowing clouds (droplets, ice crystals) that likewise change color with time. Streams of different ages would mix together in a blending of rainbow glows. The ultimate fate of any ices and liquids would be to plate out as shiny metallic lead at the end of their decay chains.


It's a charming notion, but it's really hard to imagine what kind of geology could conceivably produce such a display. On Earth, radon is measured in small fractions of a becquerel per liter of atmosphere. You would have to multiply that by several orders of magnitude --seven? eight? -- before you could get visible frost.

Okay, it's interesting to contemplate. The surface geology of a planet whose geochemistry allows 100 million times Earth's concentration of radium... is left as an exercise for the student.


Doug M.
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marsbug
post Sep 18 2015, 05:13 PM
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QUOTE (Nafnlaus @ Jul 18 2015, 06:00 PM) *
What's neat about strongly radioactive gases or liquids on the surface of a cold world? Well, let's look for a second at what would happen on a cold world with radon snow/frost.

Radon has a freezing point of 202K at 1atm - not super cold, but it would at least have to be colder than Mars. Picture a body with high radon emissions per unit area and an atmospheric temperature below the freezing point of radon. After emission, one might encounter radon snow, radon rime around vents, or other such features - possibly even (diluted) liquid in the right conditions. Liquid and solid radon have an intense radioluminescent glow. Any area that deposited in even small amounts of liquid or solid radon ice or snow would glow in the dark. Liquid radon ranges in glow color from blue-green to lilac. Solid radon changes color with time, starting out blue, then yellow, then orangish-red:

https://books.google.is/books?id=T0Iiv0BJ1E...p;q&f=false

So not only would the whole landscape be lit up, but it would be lit up with different colors based on when the material was precipitated out. And it would look different every day as the radon decayed. If there was an atmosphere (such as nitrogen), it could form glowing clouds (droplets, ice crystals) that likewise change color with time. Streams of different ages would mix together in a blending of rainbow glows. The ultimate fate of any ices and liquids would be to plate out as shiny metallic lead at the end of their decay chains.



Possibly a world orbiting a neutron star, condensd from the radio-isotope enhanced debris of the spernova. Plausible or not I am totally painting that.....


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HSchirmer
post Sep 18 2015, 06:08 PM
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QUOTE (marsbug @ Sep 18 2015, 05:13 PM) *
Possibly a world orbiting a neutron star, condensd from the radio-isotope enhanced debris of the spernova. Plausible or not I am totally painting that.....


Might not be cold enough in orbit around a neutron star...
But consider the planets re-forming from that nuclear ash, they're going through a reboot of the planet formation process, mergers and acquisitions, and perhaps, ejection from the system.

Consider it "the not-so nice model"... A post supernova dust cloud, collapsing with a mix of radioisotope drenched
asteroids and proto-planets and dwarf planets and regular sized planets.

Any of those could be ejected to become a steppenwolf-world, a dense radioactive world sailing through the night.
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MichaelPoole
post Oct 14 2015, 11:01 AM
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QUOTE (HSchirmer @ Sep 18 2015, 06:08 PM) *
Might not be cold enough in orbit around a neutron star...


The discovered neutron star worlds are actually colder than Earth. Neutron stars are hot, almost a million degrees or even more, but they are dim, because the surface area is so small. Neutron stars are tiny, just 10-20 km.
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