However, the sisters have very different characteristics. For one thing, Venus rotates far more slowly than Earth, so that a day on Venus lasts longer than a Venusian year! It also rotates the other way round to Earth, so that the sun rises in the west and sets in the east.
However, the most important difference, and the main one that makes it impossible for life to exist there, or for manned missions ever to be contemplated, is that the surface temperature on Venus averages 450 degrees Celsius. Atmospheric pressure is also enormous, being 90 times as great as that on the surface of Earth.
The main reason for the huge surface temperature is the fact that the Venusian atmosphere consists of 96% carbon dioxide, thus causing the thick cloud cover of Venus to act like extremely efficient greenhouse glass. Temperatures on Venus are therefore 100 degrees hotter than on Mercury, which is closer to the sun by about 50 million kilometres.
It has often been said that Earth risks becoming another Venus if the proportion of greenhouse gases in the atmosphere is allowed to keep rising. However, with carbon dioxide currently representing 0.4% of Earth's atmosphere it clearly has a long way to go before reaching the Venusian level!
© John Welford
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