Chlorine Atmosphere

[Red Giant]

For a sci-fi story I'm working on, I'm planning on having a world with a chlorine atmosphere. I have some questions I want answered:

1) Would the air have any other traits (what would the sky color be, etc)?

2) How would life use it?

3) Would there be any oxygen?

Thanks in advance for the answers.

[Argos]

Asimov has written a short-story on that theme. Chlorine gas is greenish yellow.

[JonClarke]

For a sci-fi story I'm working on, I'm planning on having a world with a chlorine atmosphere.

Good stuff! As Argos, said it has been done before, but only rare and wqith little contextural information

I have some questions I want answered:

1) Would the air have any other traits (what would the sky color be, etc)?

Yellow green? Murky?

2) How would life use it?

Elemental chlorine is extremely reactive so it would have to be continously generated. Biological process is one one of them. You would need a biosphere where chlorine plays the role of oxygen

3) Would there be any oxygen?

Traces perhaps (see below).

[/QUOTE]Thanks in advance for the answers. [/QUOTE]

You would need think of ways of to get a world which could have a chlorine atmosphere. It's a rare element in the universe, 17th in abundance, where oxygen is 8th. Maybe carbon planet?

Jon

[eburacum45]

This science-fictional examination of the possibilities might interest you; Chlorine Worlds Xenophotosynthesis. If anyone knows of an academic study of this subject I'd be very interested.

Chlorine, as Jon points out, is highly reactive, and would disappear from a planet's atmosphere by reacting with other elements, unless some process existed to constantly replenish it. But the same can be said of oxygen.

The process that springs to mind is life; if life processes on a world constantly produced chlorine, it could then persist in an atmosphere. I think that several highly reactive elements and compounds such as oxygen and chlorine might be produced by biological action in various diverse biospheres around the universe. Other possibilities include methane, hydrogen sulphide, carbon monoxide, even fluorine. Some of these might even act as exotic biomarkers (but like most biomarkers they will be controversial until life is confirmed).

One note of caution- chlorine is nothing like as common an element in the universe as oxygen; so atmospheres consisting completely of chlorine are unlikely. On our world the chlorine is found in the seas and oceans; but the quantity of chlorine in the sea and rocks is small compared to the amount of oxygen in the atmosphere and crust. So oxygen atmosphers may well be much more common than chlorine ones.

Here's a table of abundances for elements in the universe;
http://eg.orionsarm.com/xcms.php?r=o...=4983179dba6ac
as you can see oxygen is very much more abundant than chlorine or fluorine.

[Red Giant]

Thank you. I'll have to think of a way to concentrate chlorine then. Any ideas on how to do that?

[JonClarke]

Thank you. I'll have to think of a way to concentrate chlorine then. Any ideas on how to do that?

Some sort of atypical parental nebula composition., highly enriched in heavier elements?

Jon

[Nick Theodorakis]

I think you need to find a way for a biological process to make it.

Nick

[Nowhere Man]

A biological process is not going to create chlorine out of other elements. It simply has to be there, in one form or another.

Fred

[Nick Theodorakis]

A biological process is not going to create chlorine out of other elements. It simply has to be there, in one form or another.

Fred

I meant, to make free chlorine gas, which is reactive and needs a source to keep it in his atmosphere or it would disappear.

Maybe some kind of metabolism based on perchlorates or chloro-organics.

Nick

[Red Giant]

How about a world with abnormal levels of hydrochloric acid in the oceans? Then, photosynthesis might produce oxygen and chlorine.

[Yukmay]

Interesting idea. I have tossed around the idea of a planet with a chlorine atmosphere ever since one of my undergrad professors showed an experiment where pure chlorine gas supported the combustion of magnesium. This made me think of cavemen on some chlorine planet discovering fire. Heh.

Chlorine gas is an a strong oxidizing agent. That is to say it accepts electrons from redox reactions. Another strong oxidizing agent would be oxygen of course. In the same light one might think that an organism might use chlorine gas just as it does oxygen. However, I'm not exactly sure how this could be. Oxygen accepts electrons from NADH to create a proton gradient (energy), and then is reacted with the protons to yield water. I don't know of any elegant energy yielding reactions with chlorine such as these but they very well may exist.

As for a way to create a chlorine atmosphere...

Electrolysis of brine (NaCl) yields lye (NaOH), Chlorine (Cl2), and Hydrogen (H2).

Electrolysis of HCl should yield Chlorine and Hydrogen.

I was thinking about something like a really stormy planet with HCl droplets in the atmosphere being electrolyzed by lightening. This could make a start for the Cl2 atmosphere. Then biochemical processes could take over.

[cjameshuff]

I meant, to make free chlorine gas, which is reactive and needs a source to keep it in his atmosphere or it would disappear.

The point is that you first have to create a planet where chlorine is far more abundant than it is on Earth. There's nearly 22000 atoms of oxygen for every atom of chlorine in the universe.

One possibility...the planet's artificial, or at least its surface has deliberately been extremely modified to have an impossibly high chlorine abundance (and probably simultaneously depleted in oxygen).

[IsaacKuo]

How about a Chthonian planet where most of the oxygen blew away along with the rest of the atmosphere? But somehow a lot more chlorine survived in solid compounds like sodium chloride or PVC? I have no idea whether that's even remotely plausible...I would guess not, though.

[eburacum45]

The point is that you first have to create a planet where chlorine is far more abundant than it is on Earth. There's nearly 22000 atoms of oxygen for every atom of chlorine in the universe.

One possibility...the planet's artificial, or at least its surface has deliberately been extremely modified to have an impossibly high chlorine abundance (and probably simultaneously depleted in oxygen).

That is the option Anders Sandberg took in the original write-up for OA, nine years ago. The chlorine worlds there have all been tweaked to favour chlorine-producing biota. Possibly the long-lost race of tweakers came from a world where this had happened naturally; they proceeded to 'chloriform' lots of other worlds before dying out themselves.

I think that chlorine rich-worlds might occur naturally sometimes, as a result of astrophysical reasons rather than for geological or biological reasons. Certain stars have peculiar metal abundances- they are called 'peculiar stars', strangely enough. Perhaps a particularly rare and peculiar star might have outgassed a chlorine-rich cloud while in close proximity to the planet in question, and the local life--forms adapted to this rich source of oxidation by incorporating it into their biochemistry.

[neilzero]

In many respects chlorine behaves like oxygen, however chlorine dissolves in water to form hyproclois acid and hydrochloric acid. The first releases oxygen easily, leaving more HCl = hydrochloric acid. Oxygen and water on the other hand separate and redissolve easily, which is very important to fish. A mixture of chlorine and oxygen is possible in any ratio, briefly, but many compounds contain both chlorine and oxygen. Like the hyproclois acid, the oxygen is typically released easily. Neil

[Red Giant]

So the aquatic animals would breathe oxygen and the land based life would use oxygen and chlorine? Just want to make sure I understand that.

[Disinfo Agent]

Chlorine-breathing life seemed to be a recurring theme in early science fiction. Heinlein mentions it in some of his books, IIRC.

[tdvance]

Thank you. I'll have to think of a way to concentrate chlorine then. Any ideas on how to do that?

My first thought is the same way Earth concentrates oxygen.

Some life form liberates it. You still need something else, since it's not nearly as common as oxygen, but since it is very reactive like oxygen, even with plenty of chlorides around, free chlorine wouldn't last if it weren't continually re-freed somehow.

I.e. if we ever find a planet with lots of oxygen, or chlorine, etc. in the atmosphere, a betting man would bet there's at least unicellular life there.

[ravens_cry]

Here's an idea.An oxygen based intelligent lifeform, from an ecosystem of oxygen based life forms, uses a widespread industrial process that releases chlorine into the atmosphere, slowly poisoning the existing ecosystem, but other creatures evolve to use it, re-release it themselves, supplementing the earlier oxygen users, in a completely new ecosystem. Oxygen using life only surviving in extreme environment's toxic to the chlorine users and producers. Kind of like what happened with blue green algae and oxygen, but if blue-green algae had killed itself off in the process, and other plants took it's place as the main oxygen producers.

[IsaacKuo]

How about some sort of massive collision that vaporizes away most of the water and carbon dioxide, and throws up gobs of raw core iron into near solar orbits? These iron "meteoroids" spend the next several thousand years raining back down onto the world, locking up any remaining oxygen into iron oxide. This planet ends up somewhat like Mercury...now is there some way to get chlorine to survive this cataclysm?

[JonClarke]

How about a world with abnormal levels of hydrochloric acid in the oceans? Then, photosynthesis might produce oxygen and chlorine.

The problem is that acid-rock interactions will consume the acid, releasing sodium, calcium, magnesium, etc, and you will end up with a near neutral ocean in a geologically short period of time.

[dwmyers]

One way of having a chlorine linked biosphere would be to have an ocean rich in halogen salts. The microbes/fish/whatever could have developed protective defenses or an energy cycle based on oxidizing chlorides and creating gaseous chlorine. The halogen acids aren't likely to remain for any length of time, as they're just not stable enough, but the halogen salts are quite stable over long time scales, and very soluble.

Perhaps chloro-oxygen (chlorates, etc) compounds serve a role similar to high energy phosphates in Earth species..

The question then is, could you fill a whole atmosphere with free chlorine, and my feeling is, probably not. Nitrogen with some chlorine maybe, in earth sized planets. And there could be competition between oxygen releasing photosynthesizers and chlorine cycle lifeforms.

Downside of all that is the relative power of the chemical cycles you have. Oxygen cycles have the advantage that making water is really exothermic. Cycles that tap into that energy have a huge advantage. The formation of hydrogen chloride is, at best, a pale imitator of H2O.

Of course, there are different hypothetical rules entirely if the planet is molten hot and the "seas" are molten chloride salts.

David Myers.

[qraal]

Stephen Baxter posits a world in "Manifold: Space" which has free chlorine due to metabolism by microbes in the sea. The previous oxygen breathing biosphere adapts, more or less, to the new abundance of free chlorine, though it's a rather dangerous place, with asphyxiating amounts of chlorine close to the ground.

[timb]

One way of having a chlorine linked biosphere would be to have an ocean rich in halogen salts.

What, like ours?

The microbes/fish/whatever could have developed protective defenses or an energy cycle based on oxidizing chlorides and creating gaseous chlorine. The halogen acids aren't likely to remain for any length of time, as they're just not stable enough, but the halogen salts are quite stable over long time scales, and very soluble.

Perhaps chloro-oxygen (chlorates, etc) compounds serve a role similar to high energy phosphates in Earth species..

The question then is, could you fill a whole atmosphere with free chlorine, and my feeling is, probably not. Nitrogen with some chlorine maybe, in earth sized planets. And there could be competition between oxygen releasing photosynthesizers and chlorine cycle lifeforms.

I fail to see how. The raw materials they consume are different, and the chlorine "cycle" lifeforms are dependent on photosynthesis.