Magellan mapping unveils volcanic Venus.

NASA released new pictures last week from Magellan's first mapping cycle of Venus, revealing a surface shaped by volcanic activity and scarred with impact craters. Over a span of 243 days ending May 15, the orbiting craft's radar pierced thick clouds to capture detailed images of 84 percent of Venus' surface.

"Magellan has removed the veil from the planet Venus. We have now been able to see entirely through Venus' perpetual cloud cover," says Wesley T. Huntress Jr. of the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., who heads NASA's solar system exploration group.

Magellan found no evidence for Earth-like plate tectonics (SN: 5/4/91, p.280), but it did detect a host of unusual volcanic features, including huge lava flows and a formation shaped like a giant tick. Despite the overwhelming evidence of past volcanism, Venus' current status remains unclear. "It's highly probable that volcanism is going on right now, but it's sort of like a mystery novel: Is Venus dead or alive? We need to find the smoking volcano," says geologist James Head of Brown University in Providence, R.I.

Long considered Earth's planetary twin, Venus now appears instead to resemble the Earth of eons ago. "We're starting to realize that Venus may indeed be giving us a look into our past," says Magellan chief scientist R. Stephen Saunders of JPL.

If things go well, Magellan's radar will map all of Venus by the end of its third cycle in September 1992. NASA will then attempt to construct a global gravity map of the planet based on subtle shifts in the craft's altitude. As Magellan travels, its orbit dips and rises slightly in response to variations in gravity, which reflect the different densities of matter within the planet. Thus, the craft can provide not only a look at Venus' surface but also a glimpse into the planet's interior.