Venus may be a twin for Earth when it comes to size, but
you wouldn't want to visit!
From a distance, Venus looks like Earth's twin.
With a diameter of 12,102 kilometers, it's 95 percent
the size of our planet. With 81 percent of Earth's mass,
its gravity is just slightly less than Earth's. Looking
at Venus through a telescope, you see lots of clouds. This
gave early astronomers the idea that the planet had a warm,
humid climate capable of supporting lush jungles. Looks
can fool you! In the case of Venus, these assumptions couldn't
have been more wrong!
Venus's atmosphere is about 96 percent carbon dioxide and
only about three percent nitrogen. Clouds of sulfuric acid
are suspended in Venus's atmosphere, producing a pale yellow
haze. Like the glass roof of a greenhouse traps heat, the
carbon dioxide-rich atmosphere of Venus makes it the warmest
planet in the solar system.
This was a surprise to many scientists. When the Soviet
Union launched a series of Venera probes to the planet,
they discovered temperatures in excess of 460° C —
hotter than those on the lit side of Mercury! Because Venus
is 108,200,000 kilometers from the Sun (almost twice as far as Mercury),
astronomers expected it to be much cooler. These high temperatures
are thought to be the result of a runaway greenhouse effect.
Soviet scientists got another surprise when the probes landed. Carbon dioxide is much denser than the air we have on Earth, so the atmospheric pressure on the surface of Venus is comparable to pressures we feel under 30 meters of water.
Because of this, several of the Soviet probes were literally
crushed under the weight of the air. When one finally landed
successfully, it showed a surface that was not too different
than Earth. Minus the water, of course — which long
since boiled away!
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