Monday, November 30, 2009

Venus and the Run-Away Greenhouse Effect

The runaway greenhouse effect: So hot all the ocean's waters evaporate. So hot the carbon in rocks evaporate.

The surface of the planet so hot it could melt lead; a surface so hot that it would evaporate rock. Venus represents a greenhouse effect gone wrong, as life is unsustainable with its climate so harsh. Mars, Venus, and Earth each provide the examples of the importance of the greenhouse effect. Mars lacks a sizable greenhouse effect. Earth has the perfect greenhouse effect for life, however long that will remain true is in hot debate. And Venus in one word: hot.

Venus, at 467 degrees C is called Earth's sister planet because Venus is 95% the size of the Earth, has a rocky crust, and similar iron-nickel core. In the early years, 4.6M years ago, they both had water. They were practically twins, except for a few key traits. For starters, Venus doesn’t have a strong magnetic field like the Earth’s, an important distinction that will be examined shortly. Next, Venus is much closer to the sun so naturally it warrants higher temperatures. These days the two planets couldn't be further apart; Venus is a hot ball of carbon dioxide and sulfur clouds void of water and life. It owes its fate to a runaway greenhouse effect.

The Runaway Greenhouse Effect: initially there was water vapor. Solar radiation contains pure light and radiant heat, so it can easily pass through water vapor and other greenhouse gases of the atmosphere. Once this solar radiation (light) hits the planet, some of the light is reflected back out into space and a portion is transformed into Infrared Radiation that also tries to reflect back into space. When infrared radiation hits a greenhouse gas it is absorbed and turned into heat.

As mentioned earlier, Venus had water in the form of vapor (there was never liquid water). The sun's UV rays hit the water vapor providing enough energy to separate the hydrogen atoms from the oxygen atom. Since hydrogen makes the lightest gas it can escape the atmosphere, and in Venus's case, solar winds swept this component of water for good. In contrast, the Earth has a protective Ozone layer to keep the UV out just above the cold trap (layer of the atmosphere that freezes water if it travels too high, therefore sending it back to earth). Continual heat trapping allowed Venus to be so hot it could melt carbon rocks and eventually evaporate carbon into the atmosphere. The effect was so strong that today CO2 is 95% of Venus' atmosphere.

The greenhouse effect is essential to life. Mars is too cold and Venus too hot; the Earth is just right, for now. It would now take only 5 months to get to Venus via spaceship, or about a third of the duration of when Magellan's Spanish Galleons circumnavigated the globe. Even though Venus is 400M miles away, we're closer to it than ever before. Hopefully we'll stay as far away from its climate and runaway greenhouse effect.

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