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View Full Version : How can planets have methane atmospheres. Why doesn't it just explode & burn away?


astro
10-07-2006, 03:56 PM
Like Titan (http://www.astrobio.net/news/article1402.html)

Methane is flammable why doesn't a spark set it off?

Titan wiki (http://en.wikipedia.org/wiki/Titan_(moon))

The thick atmosphere blocks most visible wavelength light from the sun and other sources from reaching Titan's surface. It is so thick, in fact, and the gravity is so low, that a human could fly through it by flapping "wings" attached to his arms (but it would be much too cold.) The Huygens probe was unable to detect the direction of the sun during its descent, and although it was able to take images from the surface, scientists say the process was like photographing asphalt at dusk [10].


Layers of haze seen in a colorized ultraviolet image of Titan's night-side limbThe atmosphere is 98.4% nitrogen the only dense nitrogen-rich atmosphere in the solar system aside from our own with the remaining 1.6% composed of methane and only trace amounts of other gases such as hydrocarbons (including ethane, diacetylene, methylacetylene, cyanoacetylene, acetylene, propane), argon, carbon dioxide, carbon monoxide, cyanogen, hydrogen cyanide and helium.[11] The hydrocarbons are thought to form in Titan's upper atmosphere in reactions resulting from the breakup of methane by the Sun's ultraviolet light, producing a thick orange smog. Titan has no magnetic field and sometimes orbits outside Saturn's magnetosphere, directly exposing it to the solar wind. This may ionize and carry away some molecules from the top of the atmosphere.

The nitrogen ratio of 14N to 15N is 183 compared with the Earth's average of 272.[11] In the methane the isotope ratio of 12C/13C is 82.3 compared with the earth standard of 89.9.[11] The isotope ratio of H/D is 3.6 x 103 compared with 3.0 x 103 on earth. The depletion of the lighter isotope of nitrogen indicates atmospheric escapes where as the carbon and the hydrogen are far less depleted. The ratio of argon to nitrogen is 100 times less than in earth atmosphere. [11]

thirdname
10-07-2006, 04:01 PM
My WAG is that they don't have loose oxygen floating around; without an oxidixer the methane can't burn.

picunurse
10-07-2006, 04:04 PM
Because combustion has three components, fuel, igntion source (heat) and oxygen.
Since the methane atmosphere is icy cold and doesn't contain sufficent oxygen it can't combust.

Canadjun
10-07-2006, 04:12 PM
Jupiter's atmosphere (http://starryskies.com/solar_system/Jupiter/jupiter_atmoshere.html) is 82% hydrogen, and it doesn't burn for the same reason.

kanicbird
10-07-2006, 05:53 PM
BTW Titan is not a planet

(still bitter about Pluto)

Polycarp
10-07-2006, 06:24 PM
There was an interesting gimmick in an Arthur Clarke book(Imperial Earth IIRC) where someone on Titan had set up a torch effect, but instead of a jet of natural gas burning in oxygen-bearing air, as on Earth, it was a jet of oxygen burning in the hydrocarbon-complex atmosphere of Titan.

susan
10-07-2006, 06:29 PM
This should remind us not to set up our floating, oxygen-rich habitat bubbles on Titan.

Q.E.D.
10-08-2006, 12:39 AM
Because combustion has three components, fuel, igntion source (heat) and oxygen.
Since the methane atmosphere is icy cold and doesn't contain sufficent oxygen it can't combust.
Well, there may be lightning (http://adsabs.harvard.edu/abs/2001eab..conf..155L) on Titan, which would be an adequate ignition source in the presence of oxygen. As you note, however, the lack of the latter prevents combustion.

JohnT
10-08-2006, 12:42 AM
This should remind us not to set up our floating, oxygen-rich habitat bubbles on Titan.

Naw, we'll be OK as long as we don't have heat. :D

susan
10-08-2006, 12:58 AM
Though apparently lightning is not in short supply. And you just know somebody will sneak into an airlock to smoke an illegal cigarette, and just at that moment someone will ignore the telltale and manually vent the lock, and then we're all done for.

Quartz
10-08-2006, 06:53 AM
I do hope we send another probe to Titan - some sort of dirigible, perhaps.

Quartz
10-08-2006, 06:56 AM
Though apparently lightning is not in short supply.
Could lightning be a source of oxygen in Titan's atmosphere? With the immense energy in lightning dissociating oxygen from molecules?

Q.E.D.
10-08-2006, 10:26 AM
Could lightning be a source of oxygen in Titan's atmosphere? With the immense energy in lightning dissociating oxygen from molecules?
Dissociate it from what? Looking at the list posted in the OP of gasses in the atmosphere, there's none that I can see which contain any oxygen. There might be some water vapor, but not enough to make much of a difference. Any oxygen liberated by lightning will quickly become bound up again with one of the other gasses before the concentration of O2 becomes significant.

chrisk
10-08-2006, 11:16 AM
There was an interesting gimmick in an Arthur Clarke book(Imperial Earth IIRC) where someone on Titan had set up a torch effect, but instead of a jet of natural gas burning in oxygen-bearing air, as on Earth, it was a jet of oxygen burning in the hydrocarbon-complex atmosphere of Titan.

There was also an Asimov mystery where the murderer was an inorganic chemist who just got back from doing important experiments on Titan, and he set the explosive catalyst on a pure oxygen tank instead of the hydrogen tank, because he was so used to working in hydrogen-methane.

yabob
10-08-2006, 11:48 AM
BTW, the molecular weight of methane (16) is substantially less than oxygen (32) or nitrogen (28). LTA craft are going to be that much less efficient in a methane atmosphere. Nonetheless, it is a possibility for exploring Titan. In theory, you could lift a balloon with methane in Earth's atmosphere - I never heard of anybody doing it, but I wouldn't be surprised if somebody provided a link.

Squink
10-08-2006, 11:52 AM
I wouldn't be surprised if somebody provided a link.
Methane Balloon (http://jchemed.chem.wisc.edu/HS/Journal/Issues/2005/Feb/abs248.html)

yabob
10-08-2006, 12:00 PM
Methane Balloon (http://jchemed.chem.wisc.edu/HS/Journal/Issues/2005/Feb/abs248.html)
OK. I was think more along the lines of a transportation-sized balloon, not a toy balloon in a lab experiment, but it illustrates that the methane filled balloon floats.

Q.E.D.
10-08-2006, 12:22 PM
BTW, the molecular weight of methane (16) is substantially less than oxygen (32) or nitrogen (28).
Given the Titan's atmosphere is 98.4% nitrogen, I don't see this as an issue.

yabob
10-08-2006, 12:29 PM
Given the Titan's atmosphere is 98.4% nitrogen, I don't see this as an issue.
Whoops, sorry. Didn't look closely enough.

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