Launched from the space shuttle orbiter Atlantis on May 4, 1989, Magellan was a probe designed to map the surface of Venus by radar from orbit. It proved highly successful, and succeeded in mapping virtually the whole of Venus over a three-year period. It showed remarkable detail, including extensive lava flows from ancient volcanoes. It is necessary to use radar to probe Venus because the planet is covered in very thick cloud, which light cannot penetrate. Radar, however, can 'see' through the cloud. The kind of radar system Magellan used is called synthetic-aperture, or side- looking radar. It scanned the surface at an angle with pulses of radio waves. Signals representing the radio 'echoes' from the surface were returned to Earth. With computer processing, these signals were turned into high-resolution images.
