Old Joke

[james_davis_nicoll]

which this reminded me of:


Q: What can the atmosphere of a planet with thousands of bars of abiotically produced oxygen oxydize?

A: Anything it wants to.

Comments

[anzhalyumitethe.livejournal.com]

Going up on the Dragon's Gaze next week.

[james-nicoll.livejournal.com]

Sorry, didn't mean to bigfoot you.

[anzhalyumitethe.livejournal.com]

oh no worries. 9 & 10 have a bunch of habitability posts going up.

[anzhalyumitethe.livejournal.com]

Better make that the 8, 9 & 10th now.

[neowolf2.livejournal.com]

O2 on Earth is ultimately pulled out by reaction with reduced rocks and volcanic gases. Overall, the Earth is very reduced, with just a (very) thin skin of more oxidized material at the surface. So I wonder how long it would take for a planet to soak up 100-1000s of bars of O2. This might depend on the rate of weathering of the planetary surface and the rate of volcanism.

[graydon saunders (from livejournal.com)]

If the authors think there are going to be false positives for "life bearing world" due to an oxygen-rich atmosphere being detected, they must think the hypothesized atmospheres are going to stay oxygen-rich for long periods of time.

[neowolf2.livejournal.com]

I think the time constant for absorbing the O2 from Earth's atmosphere is around 10 million years (if all photosynthesis were to end), so the question is how would that rate scale up if O2 partial pressure were much higher. Billions of years isn't out of the question.

[graydon saunders (from livejournal.com)]

Earth's crust is about half oxygen, isn't it? 46% or so?

Given the mechanism being proposed, it doesn't seem implausible that a planet with no hydrosphere (because it's all been disassociated away...) and a low rate of volcanism because it doesn't have much plate tectonics (because it doesn't have much of a hydrosphere) would wind up with a completely oxidized surface.

Gotta say this is totally changing my mental images for "oxygen-rich atmosphere", too. From "oh, there's life, how convenient for our protagonist" to "don't land there, you are flammable, protagonist, flammable!"

[bruce munro (from livejournal.com)]

1000 bars of oxygen - that's sort of a "concrete burns" scenario, isn't it?

[beamjockey.livejournal.com]

I wonder what Hal Clement might have done with a setting like this.

[neowolf2.livejournal.com]

People could live on airships at the 0.3 bar level.

[neowolf2.livejournal.com]

Yes, the Earth's crust is something like 46% oxygen; when I say part of the Earth is "reduced" I mean "has some atoms not in highest oxidation states". In particular, I mean there is ferrous iron, sulfur and sulfide, as well as some other transition metals in somewhat reduced oxidation states.

Reaction with oxygen oxidizes (some of the) the ferrous iron to ferric, and the sulfide/sulfur to sulfate. Things like silicon remain in the same oxidation state (+4).

I wonder if extreme high pressure oxygen might lead to formation of unusual compounds, like perchlorates.

EDIT: BotE scribbles make me think perchlorates could be thermodynamically favored at sufficiently high pressure, if the temperature isn't too high. This could place an upper limit on the atmospheric pressure. But the near-surface carbon is going to be in the planet's atmosphere too, as CO2, so the surface is probably going to be toasty.

[bunsen-h.livejournal.com]

Fond memories...

Capt. Jonathan Archer: I understand there's an inhabited planet a few light years from here.

Lieutenant Malcolm Reed: We've detected it, sir. Sensors show a nitrogen sulfide atmosphere.

Me: You... don't know a lot of chemists, do you?

[owlmirror36.livejournal.com]

I wondered how exactly all this oxygen was supposed to have accumulated . . .

The paper says:

M dwarfs are extremely active (Reid & Hawley 2005; Scalo et al. 2007), emitting large fractions of their luminosity in the X-ray and extreme ultraviolet (jointly referred to as XUV, corresponding to wavelengths of roughly 1-1000 Å ). XUV photons are not only biologically harmful, but can drive fast atmospheric escape that leads to the erosion of planetary atmospheres

So your putative protagonist would have to worry about rather severe sunburn/radiation burn as well as catching-on-fire burn.

[neowolf2.livejournal.com]

XUV/EUV photons will not make it down to a pressure level people could live at.

[w. dow rieder (from livejournal.com)]

Heh. "Captain Daring, what are our protective suits made out of?"
"Kevlar, why?"
"Um, maybe we should talk to a chemist back at Patrol HQ before we land..."

[johnreiher.livejournal.com]

I think blocks of quartz burn level...

[ilya187.livejournal.com]

Quartz is already an oxide, so no, it won't burn no matter what the pressure is.

[johnreiher.livejournal.com]

My bad, I thought quartz was pure silicon.

[monte davis (from livejournal.com)]

There's a ClF3 gas giant nearby for that.

[tandw.livejournal.com]

I don't know; what does the oxygen activity need to be to make silicon peroxide stable?

[owlmirror36.livejournal.com]

Given that the oxygen is supposed to result from XUV radiation interacting with water (per the paper), I wondered how an ozone layer would affect this scenario. The paper doesn't mention ozone at all -- is this an oversight, or is there an obvious reason why ozone wouldn't form or wouldn't provide enough protection to slow or stop the runaway formation of the described super-oxygenated atmosphere?

[neowolf2.livejournal.com]

XUV photons are absorbed above the level of an ozone layer, and are absorbed strongly by more ordinary molecules, like water or molecular oxygen. Ozone is important only because it absorbs UV photons that are too low in energy to be absorbed by O2 or N2.

[w. dow rieder (from livejournal.com)]

"Welcome to the Thousand Bar Oxygen Bar, where everything's rock, water, or on fire!" 8-)

[scott-sanford.livejournal.com]

"For this week's exciting installment of Flashpaper Gordon!"