Venus

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

740 K.

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

similar

fate.