Talk:Atmosphere of Venus

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An entry from Atmosphere of Venus appeared on Wikipedia's Main Page in the Did you know? column on 15 August 2006.

I made some minor changes to references; I also deleted a sentence that mentioned the albedo of Venus is 0.76, since one sentence later it stated that Venus reflected 90% of the incident sunlight. The alternative to deleting this sentence would have been a long discussion of the different types of albedo (which varies with wavelength), which would have been rather off topic; people actuallly interested in albedo can look at the albedo entry.

Geoffrey.landis 15:13, 12 September 2006 (UTC)Geoff Landis

[edit] hydrogen can easily be extracted

"Hydrogen is primarily present as sulfuric acid (H2SO4), and hydrogen can easily be extracted through condensing the droplets."

Sulfuric acid does not release any hydrogen by "condensing" the droplets. On the contrary, sulfuric acid attracts and holds any water violently. Perhaps this is the reason why there is any trace of water on Venus left at all. 84.160.239.47 22:17, 17 November 2006 (UTC)

Fixed. --Xanthine 12:30, 3 January 2007 (UTC)

The article has several apparent contradictions which need to be explained in footnotes if not the main text ie "sulpher dioxide is 150 parts per million." No mention of sulpher trioxide which should be in surplus if there is "no water." It says 6 parts per million of water vapor in another part of the article. I suppose the problem is the composition of Earth's atmosphere is typically given as gas only and particulates such as dust, sulpheric acid, ice and water droplets are discussed separately. Also, Earth atmosphere scientists typically include the carbon dioxide vapor percentage, but not the water vapor percentage; just the opposite of how we have figured Venus, perhaps because the lower atmosphere of Venus is hot enough that carbon dioxide is a gas, not a vapor, as it is in Earth's atmosphere. Neil

The text includes the conjecture that Venus' atmosphere is composed of largely carbon-dioxide and nitrogen mixture because of the lack of a strong magnetic field, lighter gases not being held because of the lack of a strong magnetic field as Earth has. That would hold true also for Mars, which has a largely carbon dioxide-nitrogen atmosphere (if much thinner).

A simpler explanation exists: Venus is hot. Magnetic fields do not hold gases so effectively as does gravity. The Earth has high enough gravitation and cooler temperatures to hold gases as light as methane, ammonia, and water vapor. To be sure, the Earth's atmosphere holds little methane or ammonia because of thermodynamic instability in an oxygen-rich environment, but it holds water vapor very well. It's, of course, gravitation. A strong magnetic field may prevent some chemical reactions in the Earth's upper atmosphere, preventing the formation of such substances as sulfuric acid, but that is a different topic.

Venus is much hotter at its surface, hot enough that with gravity slighter (but not by much!) than the Earth's, Venus cannot hold gases as light as methane, ammonia, and water vapor. Much chillier than Earth, but with far lesser gravity, Mars likewise cannot hold water vapor. With their combinations of temperature and gravitation, both Mars and Venus can hold atmospheres consisting largely of carbon dioxide and nitrogen. --Paul from Michigan 01:49, 25 November 2006 (UTC)

If proponents of Gaia theory are to be believed, a major reason for the water on Earth is due to the abundant presence of life. Indeed, all living things capable of aerobic respiration produce water as a matter of discourse. Venus and Mars, on the other hand, have atmospheres relatively close to their equilibrium states (Mars more so than Venus). Interestingly enough, Lovelock discusses this in the first of his Gaia books, calculating that if Earth were to be left to form an equilibrium state (ie: if all life were somehow wiped out), it's atmosphere would be ~95% carbon dioxide and it's surface temperature would be in the region of 250 centigrade. Makes you think, doesn't it...? --Xanthine 12:30, 3 January 2007 (UTC)

Life is of course a non-equilibrium state. Under equilibrium, water would react with carbon and carbon compounds to form carbon dioxide, and with sulfur and sulfur compounds to form sulfuric acid. As is well known one can place carbon and sulfur in cold water and have no reactions.

Biochemistry itself suggests that life formed on Earth from a mixture of substances, some of which would not exist long in an oxygen-rich environment. Of course, water, carbon oxides (whether carbon monoxide or carbon dioxide), and phosphates exist. But most biochemical substances are methane derivatives. Ammonia and hydrogen sulfide would have to have existed.

Living things (plants) can synthesize methane derivatives from carbon dioxide and water and can transform mitrites and nitrates into ammonia. Some bacteria 'fix' mitrogen. But that is life at work.

Most predictions of the future of the Earth suggest that as the sun becomes more luminous, that unless the Earth's orbit becomes adequately displaced from where it is now (I believe that if humanity or some intelligent successor is around, that creature is likely to force the Earth into orbitd progressively more distant from the sun as needed), the Earth will get hotter. The Earth is toward the warm end of the life zone, and when the normal temperature on Earth approaches 45C, life will be in big trouble. Much of the biomass will die and become fuel for spectacular forest and brush fires that will thrust more carbon dioxide into the atmosphere, accelerating global warming. Higher evaporation of water will have added another greenhouse gas -- water vapor -- into the atmosphere. Atom for atom, water vapor is an even more powerful greenhouse gas.

Around 70C, the 'wet greenhouse' effect that some say occurred early on Venus takes off, and the Earth's atmosphere itself takes on the characteristics of a pressure cooker. Meanwhile, the greater pressure of the atmosphere causes the atmospheric temperature to rise in accordance with the gas laws. The process accelerates as more of the waters of the sea evaporate into the atmosphere. Some water vapor goes to the upper atmosphere and some water molecules dissociate into oxygen and hydrogen, hydrogen going off into space. Until the seas are evaporated away, there's more water vapor available to replace the water dissociated into oxygen and water.

At 305 C, the critical temperature of water, liquid water no longer exists. By then, even if the Earth has gigantic clouds protecting the planet from sunlight, pressure alone creates hothouse conditions. (Venus is hot because of the pressure of its atmosphere -- not because of the intense sunlight that shines upon cloud layers that insulate the planet). Carbonate rocks dwxompose, releasing carbon dioxide, and pressures lead to temperatures high enough to melt surface rocks.

Gory, isn't it? The earth's atmosphere would be full of oxygen from dissociated water, carbon dioxide first from the budning of biomass and petroleum and then especially the release of it from carbonate rocks, sulfuric acid from the burning of sulfur and sulfur compounds, a little nitrogen, and some water vapor. The Earth could get even hotter than Venus is today -- hot enough to melt all rock surfaces. That's all long before the Sun flares off the atmosphere and beats down upon the exposed surface of the Earth.

That all depends upon the extinction of complex life. We might not have the means -- yet -- of altering the Earth's orbit. But humanity or whatever its successor at the time (advanced pigs?) will likely cherish life enough to get the Hell out of an infernal prospect. The Gaia effect got little chance on Venus or Mars. It may need some help a few hundred milliion years hence just to continue. Sure, this is speculation, and as such 'original research'... probably forgivable in a talk page. --Paul from Michigan 10:20, 14 January 2007 (UTC)

Surely speculation is the entire point of a talk page! :) I'd love to continue this conversation, but I fear it'll soon venture too far off topic... --Xanthine 12:57, 23 January 2007 (UTC)