When astronomers first pointed their rudimentary telescopes at Venus, they saw a world shrouded in clouds. Here on Earth, clouds mean water, so early astronomers imagined a tropical world with constant rainfall. The truth, of course is that the thick atmosphere on Venus is made almost entirely of carbon dioxide. In fact, the atmospheric pressure on the surface of Venus is 92 times more than what you would experience on Earth. If the clouds are carbon dioxide, is there water on Venus.
Well, there isn’t any water on the surface of Venus, in form of rivers, lakes or oceans. The average temperature on Venus is 461.85 °C. Since water boils at 100 °C, it couldn’t be on the surface. But could water be in the clouds and atmosphere of Venus?
Astronomers have detected that the atmosphere of Venus consists of 0.002% water vapor. Compare that to the Earth’s atmosphere, which contains 0.40% water vapor.
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Scientists think that Venus had a similar formation to Earth, and it was certainly bombarded by the same comets that delivered vast quantities of water to our early planet. So why has Venus lost its water, while Earth kept its water? Recent observations by ESA’s Venus Express spacecraft found that Venus has a trail of hydrogen and oxygen atoms blasted away from the planet by the Sun’s solar winds. Every second, there are 2 x 1024 hydrogen atoms streaming away from Venus. The Earth’s magnetosphere protects our atmosphere from the Sun, channeling the solar wind around the planet, and keeping it from reaching our atmosphere.
The Earth’s magnetosphere is generated by the convection of material deep inside the Earth. This happens because the large temperature difference between the outer core and the inner core. At some point, plate tectonics on Venus ceased, and the planet stopped releasing as much heat from the interior. Without a high temperature gradient, its inner convection stopped, taking away its planet-wide magnetosphere.
It’s estimated that Earth’s atmosphere and surface has 100,000 times as much water as Venus. And if we didn’t have our protective magnetosphere, we’d be losing our water too.
We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.
We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.
NASA Ask an Astrophysicist: Water on Venus