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I'm curious what it would take to get a planet with so much free fluorine that you can have an atmosphere of predominantly or purely fluorine. I realize how improbable a planet like this is, so I'm looking for the long set of perhaps contradictory conditions that would lead to a hellscape planet like this. How do I get a planet sized ball of fluorine ash products and an atmosphere of fluorine to go with it?

Planet parameters:

  1. Earth-like in mass.
  2. Surface atmosphere of one bar
  3. Atmosphere is >70% fluorine

Points in a good answer :

  1. Organization and evolution of the proto planetary disk.
  2. Processes required to concentrate enough fluorine in one place to get a fluorine planet and fluorine atmosphere.

Out of Scope

  1. Questioning the question :) I know this planet is crazy and highly improbable. Don't tell me why it can't work. Tell me why it can and what it would take.
  2. Life. Whether this planet will support life doesn't matter to this question.
  3. Evolution of the planet past initial formation.
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    $\begingroup$ Oxygen is very reactive, but fluorine is so crazy reactive that it even reacts with the "completely" nonreactive noble gasses. Thus, it won't work. $\endgroup$ – RonJohn May 11 '17 at 4:02
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    $\begingroup$ See How to Make a Monster by Ben Bova $\endgroup$ – JDługosz May 11 '17 at 6:49
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    $\begingroup$ @green I'm sure it somehow ends in a planet with a fluorine like atmosphere ;) $\endgroup$ – Totumus Maximus May 11 '17 at 13:40
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    $\begingroup$ @TotumusMaximus Wouldn't that dissolve the turtles, tho... $\endgroup$ – kingledion May 11 '17 at 13:45
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    $\begingroup$ You can't question the question as Green already questioned the question in this question, making further questions of the question in question both circular AND redundant. $\endgroup$ – Gio May 11 '17 at 18:57
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Here goes nothing

Firstly, fluorine is not particularly abundant in the universe so you need a large source in order to get an atmosphere of it. Additionally, fluorine is easily consumed in stellar nucleosynthesis so it's hard to encounter a significant concentration for your planet forming. Anyway, let's begin!

A Star Dies

In a Red Giant star at the end of its life, it's inside is stratified with different layers of fusion occurring. In these different layers, you get different elements.Lighter in the outer layers, heavier in the center. The Star Dies in a core collapse supernova or Type II blasting its layers outward and releasing a ridiculous amount of neutrinos.

really, you should enter image description here

Deadly Neutrino Radiation

Relevant XKCD comic. Now the outflow of neutrino radiation is so great that it may be enough to knock a proton off Neon or Neutron to make Neon-19 which decays into fluorine. This process is currently speculation. The result is an expanding fluorine rich shell of gas. For the sake of argument, let's say there is a whole bunch of it. The whole system falls into a disk around the supernova remnant.

Planet-forming

Planets start forming during your standard process: accretion. These planets form in the heavy element-rich layers with no abnormalities. Except two relatively large planetesimals form and collide with each other. These two planets were not so dissimilar from Earth during the early Haden Eon. So violent is the collision that the metal-rich cores of the planets are knocked out and form a new planetesimal rich in metal.

The burning

Our new planet drifts out into the fluorine rich part of the disk and begins gathering it due to its gravity. The planet has a surface rich in nickel and iron with much fewer silicates than earth. As the planet begins to gather fluorine the surface burns. But the metal rich surface reacts with the fluorine and produces a nonreactive passive layer. The silicates burn and react and form their own layers or there is not enough silicate to react with the fluorine. As such the planet is able to keep a fluorine atmosphere for a geological period of time.

Results

A dense (why not venus atmospheric density for good measure) fluorine rich atmosphere with a whole bunch of other nasty compounds on its surface. Even More Hardcore it's also orbiting a neutron star or black hole.

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  • $\begingroup$ See my edit: don’t fake breakheads by using an all-bold paragraph. Use the header markup, which you can see on the toolbar. $\endgroup$ – JDługosz May 11 '17 at 6:44
  • $\begingroup$ Regarding "the metal rich surface reacts with the fluorine and produces a nonreactive passive layer", I don't think you are going to get that. Iron III flouride is hygroscopic and Iron II flouride readily forms a tetrahydrate. If there is any water at all on your planet, then you will end up with a souply HF ocean saturated with dissolved iron. The dissolved iron would be constant precipitating out of solution and falling to the sea floor, while other iron would be getting dissolved by the HF. $\endgroup$ – kingledion May 11 '17 at 12:21
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    $\begingroup$ @kingledion HF oceans are the clearest indicator, from space, that "here there be dragons". A foolhardy explorer wouldn't even make it to the lower atmosphere. $\endgroup$ – Green May 11 '17 at 13:43
  • $\begingroup$ @JoeKissling could you clarify what you meant by "metal-rich cores of the planets were knocked out"? Knocked out to where? $\endgroup$ – Green May 11 '17 at 13:50
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    $\begingroup$ @kingledion that is why I chose this method of planet-forming to keep the amount of water on the world very low. The hot cores of planets should have very little to begin with and residual heat should bake off most of what arrives back during re-accretion. The ocean, (lake) of HF will be small and the iron, HF reactions will get to an equilibrium between what's on the floor and what is dissolving in. Or the shores of said lake are nickel. I mean the passive layer as an average for the whole surface, as in the surface is not going to consume the entire atmosphere. $\endgroup$ – Joe Kissling May 11 '17 at 14:49
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Problem

The problem here is not the reactivity of fluorine - you can make a planet out of fluorine compounds that will be stable wrt fluorine by definition. The problem is how we concentrate enough of the stuff in one place to make it dominant.

Concentrating F

Now, what we could imagine is a highly magnetic object acting as a particle accelerator and also banding the paths of released particles - not dissimilar to a mass spectrometer on earth. So imagine a spinning neutron star ploughing through a cloud of dust released by a supernova, throwing off atoms at different angles according to their mass. These particles then impact a dense region of dust and gas, forming zones of differently concentrated elements.

Making a Planet

Now we have a freakishly fluorine-rich area, which collapses into a star and protoplanetary disk by the normal mechanisms; there is further differentiation within this disk - because the F-rich minerals have chemical properties that have them condensing at a certain distance from the new star (just as the solar system has an ice line) so we concentrate the F-containing compounds into a smaller band; this turns into a planet with a very high percentage of fluorine. We can also deliver more fluorine from icy objects outside of this band.

Planet Composition

Common elements such as silicon, carbon, and hydrogen wil be present; we'd want to minimize oxygen. We might propose that there is an iron core and silicate layer at depth in this planet, with a fluorosilicate layer above that, an ocean of HF and an atmosphere of F2.

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Read until the end, I do has he asks.

Sorry but this is in a real danger of becoming bad fiction. You don't let a baby win the Olympic marathon in a book either. Fluorine isn't created in large quantities by stars so you won't find large quantities in space. In addition to that, fluorine reacts with basically anything - even some noble gases. It's way more reactive than oxygen. Look, you not only need a rare element to form a planet, you also need common elements to be absent from said planet - like hydrogen for example (or else you would have an hydrogen fluoride atmosphere). Let's not say it was created like oxygen on this planet because 70% is way too high for that. I had a whole passage about why life can't exist on that planet and this option is out of the question, but I deleted it - felt out of place. Basic thing is: It can't happen.

Just wanting it to work doesn't make it a good idea. So here are possible solutions:

The planet has been created by a super advanced civilization as a joke and any possible life has been designed by them as well with materials we do not know of yet.

The planet was inhabited by a civilization that created fluorine as industrial waste, even collecting it throughout their star system. This ended in catastrophe.

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  • $\begingroup$ Just because we're so fascinated with non-carbon and non-oxygen based lifeforms is IMHO enough for our own civilization to try it out when we'll have the means to do so. $\endgroup$ – Agent_L May 11 '17 at 10:59
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    $\begingroup$ @Agent_L your comment ignorantly implies that life on Earth just randomly used carbon & oxygen, and that -- for example -- silicon, fluorine & arsenic would do just as well. That is far from true. Carbon's four valence bonds allow for stupendously rich chemistry, and both carbon and oxygen are stable enough to not instantly react (like fluorine does) but reactive enough to allow for the reactions we call "life". $\endgroup$ – RonJohn May 11 '17 at 15:33
  • $\begingroup$ What would be wrong with a hydrogen fluoride atmosphere in this example? It'd be 90% fluorine, just bound with hydrogen. It'd definitely make a hellscape! $\endgroup$ – Doktor J May 11 '17 at 18:54
  • $\begingroup$ By your definition, HGttG is "bad fiction". $\endgroup$ – Gio May 11 '17 at 19:03
  • $\begingroup$ @Glo in the universe there is 10^4 more carbon and oxygen than there is fluorine. But that has no bearing on my comment. $\endgroup$ – RonJohn May 11 '17 at 19:17
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Related to Raditz_35's answer:

There is a superadvanced race that is able to manipulate space to build what is in effect a cavatron that can process a whole star at once (Obviously it's working on something other than an electric current!) They haul the machine to stars that are just about to die and toss them in, the matter is scattered across space by it's charge and atomic mass.

They scoop up everything of value. They do not consider the fluorine of value.

(For those who haven't heard of them: You ionize the input material, subject it to a fixed voltage, deflect it with a magnet and catch it. The deflection is based on charge/mass, so long as you are precise enough and the buckets are placed appropriately it's quite capable of doing things like U-235/U-238 separation--and with a machine a good engineer might be able to build in his garage. We aren't buried in engineers building nukes because the power requirements are incredible--we even tried that route in the Manhattan project, it was abandoned as impractical.)

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Highly reactive species, like oxygen or fluorine, need to have some sort of cycle freeing them back in the atmosphere.

Therefore if there was some form of life which used oxydation by fluorine as energy source and some sort of plants using photosynthesis based on fluorine instead of oxygen, you could get quite some free fluorine in the atmosphere.

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  • $\begingroup$ In this question, the answer provided by Andrew Dodds takes a good poke at that. $\endgroup$ – Gio May 11 '17 at 19:05
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Ionizing radiation can release fluorine from rocks. CF "Stinking Fluorite" which is Fluorite contaminated with Uranium, in which beta particles break apart fluorite into calcium and fluorine.

https://en.wikipedia.org/wiki/Antozonite

So your hellscape just got more hellish. To keep fluorine in the atmosphere there has to be enough beta emitters in the crust and fluorites comingled to trigger its release.

So its not just poisonous but radioactive too.

The necessary beta particles could also come solar wind. Maybe the planet has a dead core and weak magnetic, so solar radiation impinges the surface unheeded.

Even more hellish.

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    $\begingroup$ Hi Daniel, welcome to Worldbuilding! Your answer doesn't really answer my question though. While I appreciate the additional information about how to make the fluorine hellscape more hellish, I'd like to hear what you have to say on how such a planet might form in the first place. $\endgroup$ – Green May 12 '17 at 0:18
  • $\begingroup$ Welcome Daniel! You can edit your answer with the little grey "edit"-button. If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus May 12 '17 at 7:19
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First problem is to get a fluorine rich planet at all. Stellar nucleosynthesis is working against this, and the remaining possibility is an engineered planet with unusual elemental composition. So as a starter, you have an advanced civilisation that builds a fluorine rich planet as kind of laboratory for planet evolution.

Second, what will the atmosphere of fluorine rich planet contain? Most probably, predominantly HF. $CF_4$ will polymerise over time given solid teflon. Probably some $SF_6$ and some $NF_3$ will be in the atmosphere, too. They are a very strong greenhouse gases leading to heating up the planet: Your hell will probably have Venus-like temperatures!

I don't expect free $F_2$ to be a major component of the atmosphere unless there is some biological activity on the planet. It will be very strange and unlikely lifeforms, but I can imagine exotic life based on carbofluorides.

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