Below Venus' thick deadly cloud cover is a planet of deep valleys and massive volcanoes. This was observed during NASA's Magellan mission which orbited Venus from 1990-1994 and Europe's current Venus Express mission which reached Venus in 2006. These spacecraft make use of radar imaging so are able to 'see' through Venus' atmosphere to map its surface. Scientists have discovered that the planet has 167 volcanoes which are larger that 100 kilometres across (only one volcano is this large on Earth) and over 50,000 smaller volcanoes. During the Magellan mission, which used spare parts from missions to other planets to keep the costs down, no volcano erupted. This disappointed scientists who were secretly hoping that the planet was geologically active like Earth and still forming.
There are no signs of water on Venus, although there may have been millions of years ago. It may have boiled away as the planet got hotter. As the planet warmed up, rivers of what might have been water appear to have been replaced by rivers of hot lava. Some scientists believe that, about 200 to 800 million years ago, the entire surface of the planet was reformed when volcanoes erupted all over it and covered its surface in lava. This explains why there are very few craters on the planet's surface, compared with planets like Mercury which are billions of years old. In this way, Venus is similar to Earth, which is also quite a young planet with very few craters. Venus also has some strange features on its surface: domes which look like pancakes and volcanoes without their usual spouts.
It is not known whether Venus is still a 'living' planet, and whether volcanoes could erupt in the future. The planet may have an iron core like Earth, surrounding by a rocky mantle (or crust). This core may still be warm, suggesting that a volcano erupting may happen again. Scientists say that they only saw Venus for a short period of time during the Magellan mission, and that a satellite orbiting the Earth and taking pictures for four years is unlikely to see any signs of geological activity taking place, such as volcanoes erupting, so the chance of seeing something similar on Venus is also slim. Venus may have been a planet similar to Earth millions of years ago - it may have had flowing water and breathable air. It may tell us what might happen to our own planet millions of years in the future.