Scientists know of more than 1,000 volcanoes on the surface of Venus, Earth’s “sister” planet. A big question has been: Are they still active? The scientists say yes. Their evidence for recent volcanic activity on Venus comes from a lava(熔岩) flow in the planet’s northern hemisphere. The flow is hotter than the rocks around, which means the lava might still be cooling off. “The flow we studied seems to be very young---it is still warm inside,” Nataliya Bondarenko said. Venus is a difficult planet to study from Earth because it is surrounded by thick clouds. Telescopes on Earth can’t see through these clouds, so the best information about Venus comes from spacecraft orbiting it. Bondarenko and her colleagues studied the lava flow using data from NASA’s Magellan mission. That spacecraft spent four years in orbit around Venus and used radar to make a map of 98 percent of the planet’s surface. On October 11th, 1994, the mission ended, and the spacecraft plunged (跌落) through Venus’ heavy cloud cover and crashed onto the planet below. While in orbit, the Magellan craft sent microwaves, which can go through Venus’ clouds, to the surface. Microwaves are invisible and can be as long as three feet. These waves are a kind of energy, like light. And like light, they bounce off surfaces. The way the waves bounced off the Venus’ surface and back to the craft supplied information that the scientists used to estimate the temperature of various parts of the planet’s surface. Bondarenko’s team found that the lava flow was hotter than its surroundings---which may mean the lava flow is in the process of cooling. The scientists say the lava flow can’t be very old because if it were, it would have cooled off enough that Magellan wouldn’t have noticed the difference in microwaves. She adds that the flow appears in a 1978 view of the surface that a craft called the Pioneer Venus Orbiter captured. 小题1:What happened to Magellan in the end?
|