Atmospheric possibilities?

[WhiteWeasel]

Just a few questions about atmospherics. I want to know if it is plausible or at least believable from a medium-hard sci-fi perspective.

Is it possible for...

-An atmosphere to be very deep (Distance from surface to space) but thin (low pressure)?

-Vice versa, very dense but low?

-With a really close moon can it's SOI be even the outermost edges of it?

-How common is O₂ in random planets?

[Warhorse]

In order: 1) Not sure, maybe with a large but low-gravity world?

2) Should be possible with a high-gravity world that has either lost most of its atmo, or never had much of one to begin with.

3) Probably not, due to the Roche Limit.

4) Technically, the answer would be "we don't know;" theoretically, the only way to get significant amounts of O2 is to have it continually be produced by life. Initial supplies tend to get quickly used up by oxidizing the local rocks and such like.

[lajoswinkler]

- depends on the planet size, star type and distance from it during the early formation. There can be some variations, but no extremes.

- same thing

- KSP doesn't model gravitational interactions as they exist in real world. In KSP, when you enter a body's SOI, the universe stops existing. It's just you and the body, which is unrealistic.

- traces in the form of ions and radicals are extremely common, almost a rule. They form by photolysis of water under ionizing radiation and parts of UV spectra. Abundant molecular oxygen is extremely reactive and exists just because there are autotrophs on the planet. It will not form otherwise, there isn't any simple spontaneous chemical mechanism for that.

If all organisms would vanish today, oxygen would be depleted probably in less than 200 years or so. It would oxidize various stuff like rocks, volcanic gases, methane, etc.

In fact, it took billion(s) of years for autotrophs to produce free oxygen until its concentrations in the atmosphere started rising. It was being spent on reductive planet surface. After most of it got oxidized, the concentrations started climbing.

[K^2]

Keep in mind that surface pressure is (roughly) the weight of the atmosphere per surface area. So if you have a lot of atmosphere, but at a very low pressure, the only thing that can be happening is that gravity is very low. And vice versa. If you have just a little bit of atmosphere, to get high pressure, there has to be very strong gravity.

In practice, however, worlds with low gravity won't be able to keep much atmosphere, and worlds with a lot of gravity will have a very thick atmosphere. So while there can be significant variation, like lajoswinkler said, no extremes.

[WhiteWeasel]

Keep in mind that surface pressure is (roughly) the weight of the atmosphere per surface area. So if you have a lot of atmosphere, but at a very low pressure, the only thing that can be happening is that gravity is very low. And vice versa. If you have just a little bit of atmosphere, to get high pressure, there has to be very strong gravity.

In practice, however, worlds with low gravity won't be able to keep much atmosphere, and worlds with a lot of gravity will have a very thick atmosphere. So while there can be significant variation, like lajoswinkler said, no extremes.

Say a 500 km planet with 1.3 ATM with a 55 km atmosphere? We could also assume the planet is rich in heavy gasses. (Say, Fluorine, Neon, Chlorine, or compounds: Ozone, Carbon Dioxide, Carbon Monoxide, Nitrous Oxides, Formaldehyde, Methane, etc). Because I was thinking of ideas for some interesting planets/moons in the discussion thread and wanted to make sure that they were at least plausible.

[K^2]

A 500km planet would have an escape velocity roughly equal to speed of sound on Earth. That's typical velocity for molecules in air. So at 300K, atmosphere is going to boil off the planet almost instantly. And if you cool the atmosphere enough to keep it around for a little bit, every single one of the gases you've mentioned are actually going to be liquid or solid.

[lajoswinkler]

Say a 500 km planet with 1.3 ATM with a 55 km atmosphere? We could also assume the planet is rich in heavy gasses. (Say, Fluorine, Neon, Chlorine, or compounds: Ozone, Carbon Dioxide, Carbon Monoxide, Nitrous Oxides, Formaldehyde, Methane, etc). Because I was thinking of ideas for some interesting planets/moons in the discussion thread and wanted to make sure that they were at least plausible.

Let me just add that, unless we're talking about traces (mineral inclusions, ephemeral occurences like ozone right after lightning strike, etc.), fluorine, chlorine and ozone will not be able to exist just like oxygen. Fluorine and chlorine are very reactive and will react with water very fast. Any free halogen is out of the question, that's why the notion that Eve has iodine atmosphere is preposterous.

Ozone exists in small amounts just because there's oxygen that's pounded by hard UV rays, so if there's no oxygen, there's no ozone. NOx is just like ozone.

Carbon(I) oxide can exist in reductive atmospheres on planetary bodies with high volcanic activity, and is in an equilibrium with carbon(II) oxide.

Formaldehyde can exist in small amounts on planetary bodies. It's an aldehyde, a type of organic compound that's quite reactive and tends to get oxidized or reduced, depending on the environment.

Methane is abundant in reductive atmospheres. You can't go wrong with nitrogen and methane.

Edited December 13, 2013 by lajoswinkler

[brdavis]

If all organisms would vanish today, oxygen would be depleted probably in less than 200 years or so. It would oxidize various stuff like rocks, volcanic gases, methane, etc.

Whoa. Really? Do you have a source, or a BotE calc for this? There's a whole lot of oxygen in the Earth's atmosphere… and not a lot of reduced stuff like methane or reduced sulfur compounds being produced by volcanoes. Yes, the atmosphere will eventually go from oxidized to natural (or even reduced), but a timescale of a couple centuries seems *amazingly* short - I would have guessed a couple million to several tens of millions of years, minimum. Rocks aren't going to oxidize - they already are. The same for the current sulfur compounds and iron compounds in the surface and crust (oxidizing those in the first place is where the bulk of photosynthetic O2 went… but those reservoirs have been fully oxidized, which is exactly why we managed to build up an oxygen-rixh atmosphere after. source? Help a Kerbal out.

[lajoswinkler]

Whoa. Really? Do you have a source, or a BotE calc for this? There's a whole lot of oxygen in the Earth's atmosphere… and not a lot of reduced stuff like methane or reduced sulfur compounds being produced by volcanoes. Yes, the atmosphere will eventually go from oxidized to natural (or even reduced), but a timescale of a couple centuries seems *amazingly* short - I would have guessed a couple million to several tens of millions of years, minimum. Rocks aren't going to oxidize - they already are. The same for the current sulfur compounds and iron compounds in the surface and crust (oxidizing those in the first place is where the bulk of photosynthetic O2 went… but those reservoirs have been fully oxidized, which is exactly why we managed to build up an oxygen-rixh atmosphere after. source? Help a Kerbal out.

Huh, it was in one of my college textbooks. Don't take it literally, it's on the order of few hundred years, not exactly 200 years.

Consider oceans, which would be anoxic below few metres if there wasn't any vertical mixing. They are a source of reducing agents such as methane, seeping from the depths.

If all life on Earth would vanish in one single moment, only geological processes would slowly reduce oxygen to compounds and that would last longer. Maybe couple thousands of years, hundreds of years give or take?

If all autotrophs would vanish, with heterotrophs remaining, remaining oxygen consumption (mostly bacterial decomposition after they die during few years or less) could really suck up O2 in an amazingly short time.

The rotting of organic materials and release of hydrogen sulfide and methane would gulp up oxygen like a charm.

[WhiteWeasel]

What about laythe? It has oxygen and no life on it.

[lajoswinkler]

What about laythe? It has oxygen and no life on it.

I don't know, maybe because Laythe is a part of a computer game and not a real world planetary body?

[Nuke]

well lathe has oceans, it could be full of some kind of oxygen producing bacteria, perhaps living off of geothermal vents on the sea floor. i can understand how the surface is totally uninhabitable due to radiation. but a few meters of water is all you need to shield any organisms that might be living below. then comes the question how is laythe keeping its atmosphere. magnetic field? and if so, how is it interacting with jool's?

but we have plenty of real world examples of a moon around a gas giant having an atmosphere, but we dont know of any that have liquid water. whatever lathe's oceans would be made of, it would need to be something fairly inert.

Edited December 14, 2013 by Nuke

[WhiteWeasel]

I don't know, maybe because Laythe is a part of a computer game and not a real world planetary body?

I probably should have made this clear from the start: I was exploring possibilities for the planets discussion and I wanted to see if it's plausible in the KSP universe, not necessarily real life. Although bonus points for being more probable.

Edited December 14, 2013 by WhiteWeasel