The Science of Sustainability

Global Warming on Venus?

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Credit: T. Credner & S. Kohle, AlltheSky.comYou may be surprised to hear that Venus is the warmest planet in the solar system. Venus has an average temperature of 850 degrees Fahrenheit. This is much warmer than the Earth, at 60 degrees, and even warmer than Mercury, which sits much closer to the sun, at 350 degrees. A reader asked if the high temperature on Venus was related to the composition of the atmosphere.

It turns out that the atmosphere of Venus is actually made almost entirely of carbon dioxide, and a lot of it. Because of this thick atmosphere and clouds of reflective sulfuric acid, not much was known about the planet's surface until recently. Before 1960, astronomers couldn't even estimate the length of one day on Venus! Now satellites, like the Venus Express, orbit around the planet and landers, like the Soviet Venera, have reached the surface.

We now know that the surface of Venus is scarred with impact craters, lava flows and more volcanoes than any other planet in the solar system. We know that the atmosphere is almost entirely carbon dioxide and that this atmosphere is responsible for severe global warming on the planet. However, we don't know if any of these volcanoes are still active, how much water was originally present, or if conditions were ever conducive to life.

Reading the stats on Venus got me thinking about the conditions on the other planets. Looking for the details, I came across a nice website dedicated to the solar system, www.nineplanets.org. Although each planet has a very complex composition, I list here only the one or two most common gases in each planet's atmosphere. Mercury: essentially no atmosphere; Venus: almost 100 times pressure at Earth's surface, mostly carbon dioxide, very hot; Earth: roughly 78% nitrogen and 21% oxygen, very little carbon dioxide; Mars: Very thin, atmospheric pressure 100 times less than Earth, mostly carbon dioxide; Jupiter: atmosphere indistinguishable from surface, 90% hydrogen and 10% helium; Saturn: 75% hydrogen, 25% helium; Uranus: 83% hydrogen, 15% helium; Neptune: mostly hydrogen and helium.

In reading over the description of the planetary atmospheres, you may notice some interesting trends. For one thing, the Earth definitely stands out with its atmosphere of nitrogen and oxygen. Maybe all of the life on Earth's surface is responsible? Maybe the water??

You may also notice that the planets which are furthest from the sun are made up almost entirely of hydrogen and helium. In composition, the gaseous outer planets actually resemble the original nebula that gave birth to the solar system, a feature not shared with the inner rocky planets. Why did all of the hydrogen and helium disappear from the inner planets? For that matter, where is the atmosphere of Mercury?

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.

latitude: 37.6797, longitude: -121.698

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Kyle S. Dawson

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Kyle Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.
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  • Carl Rooker

    I have heard the theory that carbon dioxide and it's green house effect is the cause of the high temperature on Venus.

    However, (as is pointed out in the 1st article) the atmospheric pressure of Venus is 90 times that of the Earth. It's atmosphere has far more matter in it to hold heat, carbon dioxide regardless.

    Also, Venus is much closer to the sun than the earth is. Because of the inverse square law Venus gets far more energy from the sun than the earth does.

    The percentage of CO2 in the atmosphere of Venus is about 95%. On the Earth it is .038%.

    Now, Mars also has an atmosphere of about 95% CO2, but an atmospheric pressue of about 1/100 of the Earth's. It is also much further than the Earth from the sun.

    The conclusion is that the high temperature of Venus is due to it's proximity to the sun, and it's extremely large mass of atmosphere, not due to it being just CO2. If CO2 were the main reason for it's heat, then Mars would be far warmer than it is.

  • Carl Rooker

    A couple of other points;

    As is mentioned in the original post, Venus has a 90 times greater pressure than the earth does. When a gas is put under pressure, it heats up. At 90 times that of the Earth's pressure that would be about 1350 lbs per square inch (versus The Earth's 15 psi).

    Also, Venus and Mars have no global dipole magnetic field. Some theories state that the lack of such a magnetic field accounts for Mars not having much atmosthere. The Solar wind has stripped it away. Earth's magnetic field protects our atmosphere from this fate.

    Why does Venus have such a massive atmosphere if it has no such magnetic field? Venus is larger, and thus has more gravity than Mars, but after 4.5 billions years you would think that Venus proximity to the Sun (versus Mars) would strip away the atmosphere to a very large degree.

    Maybe Venus' volcanoes are responsible for there still being an atmosphere, it's density, and the heat of the atmosphere. This would be due to the heat escaping the interior of Venus, and the compression of it's atmoshpere due to gases being added at a catostrophic rate.

  • nick c

    How much sun light actually penetrates to the surface of Venus? Considering the high albedo (reflectivity) of the cloud tops and the density and lack of transparency of the atmosphere, I would wonder if Venus' surface does not get LESS sunlight than the Earths' surface?

  • Carl Rooker

    Good point.

    http://www.astronomytoday.com/astronomy/venus.html states that the albedo of Venus is .76.

    If I am understanding this correctly (I may not be), then the upper clouds of Venus reflect 76% of the light that falls on them.

    I think you have just demonstrated that the temperature of Venus can not be due to solar heating even with the high CO2 content of it's atmosphere.

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