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Venus is the second planet from the sun and the sixth largest. Venus’
orbit is the most circular of any planet, with an eccentricy of less than 1%.
Venus, perhaps because it is the brightest of planets known to the ancients,
Is named after the Greek goddess of love and beauty. The planet of Venus
has been known since prehistoric times and is the brightest object in the
sky with the exception of the sun and the moon.
Venus’ rotation is somewhat unusual in that it is both very slow ( 243
Earth days per Venus day) and retrograde. In addition, the periods of
Venus’ rotation and of its orbit are synchronized such that it always
presents the same face toward Earth when the two planets are at their
closest approach. The pressure of the planet’s atmosphere at the surface is
90 atmospheres and is composed mostly of carbon dioxide. There are
several layers of clouds which are many kilometers thick and composed of
sulfuric acid. This dense atmosphere produces a run-away greenhouse
effect that raises Venus’ surface temperature by about 400 degrees to over
The planet of Venus is often regarded as Earth’s sister planet, in
some ways they are very similar. For example, Venus is only slightly
smaller than Earth (95% of Earth’s diameter, 80% of Earth’s mass.) Both
have few craters indicating relatively young surfaces. Their densities and
chemical compositions are also similar. Because of these similarities, it
was once thought that below it’s dense clouds, Venus might be very
earthlike, perhaps to the point of containing life. However, a more detailed
study of Venus revealed that many aspects of Venus’ atmosphere was much
different from that of Earth.
There are no small craters on Venus. It appears that small
meteoroids burn up in Venus’ dense atmosphere before reaching the
surface. Craters on Venus seem to come in bunches indicating that the
large meteoroids that do reach the surface usually break up in the
atmosphere. The oldest terrains on Venus seem to be about 800 million
years old. Extensive volcanisms at the time wiped out the earlier surface
including any large craters from early Venus’ history.
The interior of Venus is probably very similar to that of Earth. It
consists of an iron core about 3000 km in radius, a molten rocky mantle
comprising the majority of the planet. Venus probably once had large
amounts of water like Earth but it all boiled away, leaving Venus quite dry.
If Earth had been just a little closer to the sun, it would have had a
fate. Much of the planets’ surface is covered with lava flows and there are
several large shield volcanoes. Recently announced findings show that
Venus is still volcanically active, but only in a few hot spots. For the
part it has been geologically rather quiet for the past few hundred million
years despite their presence.
The brightness of Venus and it’s periodic proximity to the Earth
have made Venus an easy target for advances in astronomical observations.
Venus has been the object of telescopic observation from the beginning.
The appearance of the phases of Venus by Galileo was a milestone in the
modern understanding of the solar system. Early measurements of the
speed of light were derived from observations of the transit of Venus
across the solar disk as seen from the Earth. Venus was also the first solar
system object from which radar signals were first bounced off in the late
1960’s. The first radar observations of another planet from an orbiting
platform were made from an orbiting platform were made at Venus by the
Venera 15 spacecraft and were followed by Pioneer Venus Orbiter and
subsequently by Magellan.
The launch of the Mariner 2 spacecraft in 1962 started the modern
era of Venus exploration by space-craft. Since then, Venus has been
observed by spacecrafts Mariner 5, Mariner 10, and the Soviet. While
these space missions have greatly changed our view of Venus as well as
furthered our knowledge, many important questions about Venus and it’s
atmosphere remain unanswered. Why is the rotation of Venus’ atmosphere
many times faster than the underlying planet? How does Venus lose it’s
heat? We may never know.
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Mariner program, Venus, Synthetic aperture radar, Planetary science, Terrestrial planets, Venera, Magellan, Pioneer Venus Orbiter, Mariner 2, Mariner 10, Mariner 5, Planet
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