These clouds permanently shroud Venus' solid surface.
Polar regions are bright, possibly due to a haze of small particles that lie above the main clouds.
Dark regions are locations near the cloud tops where the level of sulfur dioxide is greatest. Cloud patterns travel east to west along with the Venus' prevailing winds, making a complete circuit around the planet in four days. Magellan made maps using radar to look through the clouds. The scattered dark patches in this image are halos surrounding some of the younger impact craters. This global data set reveals a number of craters consistent with an average Venus surface age of 300 million to 500 million years.