ASTRONOMERS have glimpsed the surface of Venus for the first time in 10 years
by turning the world鈥檚 two largest radio telescopes into a giant radar
scanner.
Most astronomy is based simply on observing the light or other radiation
reaching us from objects in space. This can鈥檛 tell us about the surface of Venus
because it is hidden by thick clouds.
A team led by Donald Campbell of Cornell University, using the Arecibo
telescope in Puerto Rico, got round this problem by firing a beam of radio waves
at the planet. While visible light is scattered by the cloud cover, radio waves
pass through unhindered.
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The signal bounced off the Venusian surface and was picked up by both Arecibo
and the Green Bank Telescope in West Virginia. Computers then built up an image
of Venus鈥檚 surface by analysing these echoes.
Arecibo, a 305-metre-wide dish built into a natural depression, is the
largest telescope in the world. The 100-metre Green Bank Telescope, the world鈥檚
largest steerable dish, was only completed last year, and this is its first
scientific result. Together the two dishes produced images of Venus that reveal
features as small as 1 kilometre across. And because they were peering at Venus
from slightly different angles, the data can be combined to produce
three-dimensional maps of the planet鈥檚 surface.
Venus is about the same size as Earth. But its surface roasts at temperatures
of more than 450 掳C, and concentrated sulphuric acid rains down. Some 10
years ago, NASA mapped most of Venus鈥檚 surface using the radar system on the
Magellan spacecraft. This revealed a number of volcanoes and researchers will
use the latest radar maps to look for changes on the surface that might indicate
whether the volcanoes have been active during the intervening 10 years.
鈥淐omparing the data might also allow them to see if the flanks of a mountain
have changed their shape due to volcanic stresses,鈥� says Barrie Jones of the
Open University in Milton Keynes. According to one theory, Venus may store up
all its volcanic activity for a single planet-wide eruption every 500 million
years or so. If so, this second method of analysis would be crucial.
On Earth, volcanism is caused by the movement of tectonic plates. There is no
evidence that this happens on Venus, perhaps because the planet lacks water. 鈥淚t
is possible that water 鈥榣ubricates鈥� the plate motion on the Earth,鈥� says Jones.
鈥淭he desiccation of Venus might have resulted in plates that were too rigid to
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