Venus

At a glance, Venus and the Earth have many similar traits. They share almost the same size and weight, both orbit relatively close to the Sun, and contain similar amounts of several key elements. Before short-ranged observations of the planet occurred, many people speculated that the pale yellow clouds of Venus hid a warm, wet planet teeming with life. Nothing could be further from the truth.

Venus is a dry and lifeless sphere. Long ago carbon dioxide in the atmosphere trapped the heat of the sun, boiling away what may have been huge oceans. Volcanic eruptions on the surface filled the skies with clouds of sulphuric acid, which gust around the planet at speeds as high as 360 kilometres per hour. The thick atmosphere pushes down on the surface with a pressure 90 times greater than on Earth (As much pressure as felt by a submarine at a depth of 3000 feet).

If you could survive the suffocating temperature and pressure and walk on Venus you would notice a strange phenomenon - distant objects would be distorted, and you would be able to see beyond the misshapen horizon of the planet. The abnormally thick atmosphere tends to refract light towards the surface of the planet, and this curved light would result in a bizarre 'fish eye' perspective of Venus.

Radar observations have managed to penetrate through the dense clouds to reveal an extremely smooth surface, lacking any deep ravines or large mountain ranges. There is evidence of craters, formed when large meteorites crashed through the dense cloud cover, as well as some geological activity.

Every planet in the solar system has strange and unexplained features, and in the case of Venus it's the spin. Venus is the only planet which spins backwards, all the others move in the same direction as their orbit. This unexplained feature might be due to gravitational interactions with the Sun, which slowed the spin to its current value of 243 Earth days.