A1.  The atmosphere of Venus is 100% cloudy – no images of the surface can be obtained from space. However, radio waves do penetrate through the atmosphere, so radar techniques can be used to map the surface. A radar unit sends out radio waves and receives the reflected beam. By timing how long it took the waves to return, a map of surface features can be made.

A2.  We know the surface of Venus is very young (geologically) because there are very few craters on the surface. The older a surface is the more craters it will have. Venus’ surface has been recently covered by volcanic outflows, which have covered the entire surface.

A3.  Small meteors will burn up entirely in Venus’ dense atmosphere. Thus, small craters will not form on Venus. All large craters on Venus have been flooded by lava, which indicates that molten material is available just under the surface.

A4.  Virtually all of the surface of Venus has been covered recently by volcanic outflows. We know the surface is relatively young because very few craters are seen on the surface.

A5.  Craters are very rare on the surface, as shown in radar maps. There is no evidence of folding where plates collide or ridges where plates separate, so plate tectonics has not had a major effect on the surface. Photos from the surface show sharp cornered rocks which show little erosion, which suggests that erosion has not played a major role in shaping the surface.

A1.  Because of its higher temperature, Venus' water has always been in gaseous form. Any water that reaches the top of the atmosphere through natural circulation is exposed to the sun's ultraviolet radiation. This radiation breaks the water molecule and releases a hydrogen atom. Such a light atom easily escapes the gravitational pull of the planet, making it impossible to ever rebuild the water molecule that broke down. Thus, Venus has gradually lost almost all of its water.

A2.  Venus atmosphere is very hot (about 900 ^oF at the surface) and dense (90x Earth’s atmospheric pressure at the surface). It is composed mostly of CO₂. The dense CO₂ atmosphere generates a very powerful greenhouse effect, which produces the high temperature.

A3.  Venus began with a moist and mild greenhouse effect. Little by little water was destroyed when it reached the upper atmosphere and was exposed to ultraviolet radiation. Without water, there was no way to prevent the continuing buildup of CO₂ as it was released by volcanoes. As a denser atmosphere built up, the greenhouse effect became even stronger, which released still more gas from the surface. 

A4.  When water molecules are exposed to ultraviolet light from the sun, they are broken apart. The individual hydrogen atoms are so light that they are very easily lost from the atmosphere, so that the water molecule can never reform.

A5.  Venus’ atmosphere is much denser than our atmosphere because there is no liquid water on Venus to dissolve the carbon dioxide. On Earth most of the carbon dioxide released by volcanoes has dissolved in the water and reacted with minerals in the water to form carbonate rocks. On Mars, the volcanoes that release gases have all become extinct. Without any source of new gas, the atmosphere is slowly diminishing as more of it leaks away from the relatively weak force of gravity at Mars.

A6.  Venus’ atmosphere is much denser than ours, which causes the greenhouse effect to be much stronger. The increased density is the result of the absence of liquid water on the surface of Venus. On Earth, when gasses are released by volcanoes, much of the gas slowly dissolves in the oceans and is converted back into rock by reacting with minerals in the water. Because Venus has never had oceans, gasses released by volcanoes have slowly accumulated in the atmosphere.