Sunday, 13 May, 2001, 20:25 GMT 21:25 UK

Radar looks for changes on Venus

By BBC News Online science editor Dr David Whitehouse

The world's two largest radio telescopes have combined to peer beneath the perpetual cloud cover of Venus to reveal new details of the planet's surface.

Radio pulses were transmitted from the Arecibo radio telescope in Puerto Rico, bounced off Venus, and then picked up again by both the Arecibo and the new Robert C Byrd Green Bank Telescope (GBT) in West Virginia, US.

Only radar can see what lies underneath the brilliant white clouds that permanently cover the second planet out from the Sun.

And astronomers say that the combination of the GBT, the world's largest fully steerable radio dish, and the Arecibo dish, the world's most powerful radar, makes for an unmatched tool for studying Venus and other Solar System objects.

Active planet

"Having a really big telescope like the new Green Bank Telescope to receive the radar echoes from small asteroids that are really close to the Earth and from very distant objects like Titan, the large moon of Saturn, will be a real boon to radar studies of the Solar System," said Professor Donald Campbell, of Cornell University.

A decade ago, the radar system on Nasa's Magellan spacecraft that circled the planet, probed the clouds of Venus to reveal its surface in detail.

These new studies using the GBT and Arecibo, the first since Magellan to cover large areas of the planet's surface, will provide images showing surface features as small as about one kilometre (0.6 miles) across.

The resulting images of the surface "are the first of many scientific contributions to come from the Robert C Byrd Green Bank Telescope, and a great way for it to begin its scientific career" said Paul Vanden Bout, director of the National Radio Astronomy Observatory (NRAO).

Venus may be a geologically active planet similar to the Earth. The new images will be used to look for changes due to volcanic activity, landslides and other processes that may have modified the planet since the Magellan mission.

-- Anonymous, May 13, 2001