The planet Venus is still geologically active in places, even though radar images of its surface indicate that little has changed in the past half-billion years, a scientist working on data from NASA's Magellan mission has found. Dr. Suzanne Smrekar, a geophysicist at NASA's Jet Propulsion Laboratory, said her studies, based on Magellan spacecraft altimetry and gravity data, suggest that there are at least two, and possibly more, active hot spots on Venus. Smrekar earlier presented her findings before a meeting of the Lunar and Planetary Society in Houston, Texas. The Magellan spacecraft went into orbit around Venus in August of 1990 and, over the next two years, mapped about 98 percent of the planet's surface with imaging radar. It then began to gather gravity data to help scientists develop a model of the planet's interior.
Gravity is measured using only the spacecraft's radio signal.
This technique allows ground controllers to measure the spacecraft's speed in orbit as it increases in velocity over regions of high density or slows down over regions of lesser density. Magellan's altimetry instrument measured the height of features on the surface of the planet. Top loading is evidence of a large mass, such as a mountain or volcano, pushing down on the crustal plate. At hot spots, bottom loading indicates an upwelling of less dense and, therefore, hotter material beneath the surface. As it nears the surface, it produces volcanism.