Venus is 12,100 kilometres across, about the same size as the Earth. However, it has one of the most hostile environments in the Solar System. The shining white 'surface' of the planet – which makes it the second brightest object in the night sky after the Moon – is actually an atmosphere filled with carbon dioxide and sulphur dioxide-rich clouds. From the clouds a rain of sulphuric acid droplets continually falls on the rocky surface.

The atmosphere absorbs heat from the Sun, so that the air temperature is about 480 degrees centigrade (an extreme form of the Earth's Greenhouse Effect) and it is actually hotter than Mercury, a planet much closer to the Sun.

It is believed Venus has a molten core similar to the Earth's. Rocks on Venus are also similar to those found on the Earth's continents (granite) and below the Earth's oceans (basalt). Venus does not have a magnetic field, but it probably did have oceans of water – before the Greenhouse Effect caused them to boil away.

Venus is 108 million kilometres from the Sun, orbiting once every 225 days and spinning on its axis only once every 243 days.