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Does Venus Contain Water

Venus contains little water on its surface and in its atmosphere. Scientist believe that, because of an extreme greenhouse effect, any water vapor had enough kinetic energy to attain high altitudes where solar wind broke up the water molecules, releasing the hydrogen into space.
  1. Earth versus Venus

    • Considering that Venus is of similar size and one of the two closest planets to Earth, one would expect an amount of water similar to that of Earth's, if not necessarily in liquid form.

      In fact, Venus did have more water than today when it was formed billions of years ago.

    Where Did the Water Go?

    • Where the water went is a matter of its hydrogen component being boiled away. How this happened is a matter of how Venus became hot.

    Venusian Temperatures

    • Water existed on Venus, but not as a liquid. It is too close to the sun for that. The water was suspended in the atmosphere as a vapor. Water vapor is a greenhouse gas. It lets visible radiation from the sun in, but slows its re-emission out to space after it hits the ground and becomes infrared.

      The heat from this greenhouse effect unlocked carbon dioxide locked in the rocks on the surface of Venus. Carbon dioxide is also a greenhouse gas. Venus therefore heated up more and more, in a runaway greenhouse effect that fed on itself.

    Kinetic Energy

    • We experience the kinetic energy of molecules as heat. As the atmosphere became hotter and hotter, the water vapor molecules gained enough kinetic energy to reach high altitudes in the atmosphere where protection from the sun was minimal.

    Dissociation

    • At these high altitudes, ultraviolet light from the sun could dissociate oxygen in water molecules from hydrogen. A diatomic hydrogen molecule would form, and be light enough to escape, just as has happened on Earth. The higher-mass, slower-moving oxygen would recombine with carbon and sulfur to make oxides.

    Why This Doesn't Happen on Earth

    • First, the Earth is far enough from the sun that liquid water can form. Therefore, it doesn't create a runaway greenhouse effect, nor is it heated enough to reach the high altitudes where ultraviolet light gets through. Ozone in the Earth's upper atmosphere protects water below from ultraviolet light.

    Is There Any Water Left on Venus?

    • Yes, that is how we're able to know what happened. The hydrogen in Venusian water vapor still remaining is preferentially deuterium. Deuterium is heavier than ordinary hydrogen because it has a neutron in its nucleus. This added weight makes it less likely to reach the high altitudes where UV light performs dissociation.

      Since there is still water vapor on Venus, the hydrogen-stripping process on Venus is continuing to this day. It was quantified by a visiting spacecraft in 2008. Earth's oceans and atmosphere contain 100,000 times the water on Venus.


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