urgentNEWLN: Surface change seen on Venu sNEWLN: WILLIAM HARWOOD UPI Science Writer
NASA's Magellan probe has discovered a giant landslide on Venus that apparently was triggered by a 'venusquake' measuring 5 on the Richter scale, a major discovery showing the hellish planet may be geologically active, scientists announced Friday.
Project scientist Stephen Saunders at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said radar images taken by Magellan July 23 clearly show a landslide measuring 1.8 miles wide and 4.7 miles long that was not present when the spacecraft sailed over the same area in November.
The discovery, made Thursday night based on before-and-after images of the area, marks the first direct evidence of a change on the surface of Venus since Magellan began mapping the planet in 1989.
'The best explanation that we've come up with is we're seeing a giant landslide,' Saunders said. 'We think what's happened is a large amount of material ... has slumped and flowed out across this area. It's very exciting.'
He said the most likely cause of the landslide was 'an earthquake, or a venusquake, if you will. That's a likely thing.'
'It's something like the equivalent of a magnitude 5 earthquake (on the Richter scale),' Saunders said. 'It may be that Venus is still alive.'
Wesley Huntress, director of NASA's solar system exploration division in Washington, called the landslide a 'major discovery.'
'What we have are before-and-after images which show distinct evidence of significant change that must have occurred between the times we took these images,' he said. 'It shows that Venus is geologically alive in the same sense that the Earth is geologically alive.'
While the new images are the first to show a change on the planet's surface, Saunders said he remains confident Venus is volcanically active. Lava from planet-wide volcanism apparently resurfaces vast areas of Venus every 500 million years or so. But so far, no direct evidence has been found.
The Magellan probe, launched from the shuttle Atlantis on May 4, 1989, slipped into orbit around Venus on Aug. 19, 1990. The solar- powered spacecraft uses radar beams instead of visible light to 'see' through the thick clouds that perpetually block the planet's surface from view.
The resulting data can be processed by computers on Earth to create photograph-like images of Venus's surface, showing features as small as 350 feet across -- about the size of a football field -- and 10 times better than the best previous data. The data also can be used to make dramatic movies.
The landslide was discovered Thursday night by a Magellan project scientist studying two views of Aphrodite Terra, an area of equatorial highlands marked by steep mountains and heavily fractured terrain.
When Magellan flew over the area last November, no such landslide was visible. But when the spacecraft sailed over July 23, it recorded a massive shift of surface material -- some 3,924 cubic yards. It was the first direct evidence that Venus is still undergoing geological change.
Despite recently resolved computer problems that have occasionally knocked the craft out of contact with Earth, Magellan completed its initial survey of Venus on May 15, mapping 84 percent of the planet's surface.
Since then, the probe has been filling in gaps in the initial survey and mapping more of the southern hemisphere, repeating previous observations and allowing scientists to look for changes.
NASA scientists reported Thursday that Magellan had discovered the longest known channel in the solar system, a geological scar longer than the Nile River.
JPL researchers said they do not know what formed the channel, which measures about 1 mile across and runs for about 4,200 miles in a winding, smoothly curved course across the plains of Venus.
Numerous smaller channels have been detected by Magellan, some of which apparently were carved out by lava from volcanic eruptions. But it is unlikely that lava, even at very high temperatures, would have the very high rate of flow needed to form the newly discovered channel.
In many ways, Venus is Earth's twin in the solar system. Both planets are similar in size and mass; both are relatively close to the sun, and both probably were almost identical very early in the history of the solar system.
But somewhere along the way, the environments of Venus and Earth diverged, leaving Venus the victim of a runaway greenhouse effect in which the solar radiation trapped by the planet's thick cloud cover produces surface temperatures of 900 degrees Fahrenheit -- hot enough to melt lead -- and pressures comparable to those found at an ocean depth of 2,500 to 3,000 feet.