Introduction
Venus is the second planet from the sun and is often known as Earth's sister
planet because it is closest to us. Its diameter is 12,104km, has a mass of
about 81.5% of Earth's and its density is 5.25g/cm3.
Being bright and close to Earth, Venus can be view through a telescope on Earth.
It looks like a crescent at times and at other times has a gibbous
shape. Due to its dense atmosphere, it is not possible to see the surface of
Venus from the Earth or space.
Atmosphere
Although Venus looks very much like Earth from afar, its atmospheric
conditions are very different.
Due to the presence of carbon dioxide and small amounts of sulphur dioxide,
sulphur and water, thick dense clouds made of sulphuric acid droplets are found
in the atmosphere.
The surface atmospheric pressure is 90 times higher than Earth. Instead of a
balmy 300 K surface temperature like Earth, Venus has a scorching surface
temperature of 750K!
The figures above show the variation of pressure and temperature together with
altitude for both planets.
The Greenhouse effect accounts
for the high surface temperature of Venus.
The dense Venusian atmosphere, made up almost entirely of carbon dioxide (a
greenhouse gas), absorbs about 99% of the infra red radiation emitted by the
surface.
Therefore, heat is trapped in between the atmosphere and the surface, and
temperature builds up.
Special Feature
The surface of Venus is very interesting because of volcanic activities. There is a large volcano, Gula Mons, that has a height of 3 km. 4 dome-shaped structures can be found on Alpha Regio. They originated from the retreat of lava leaving a thin solid crust that collapsed inwards. The largest volcanic structures on Venus are known as coronas. They are huge circular regions probably caused by the upwelling of mantle material.
