listen to part of a lecture in an astronomy class

P: Earth and the planet Venus are neighbors. They're approximately the same size and have approximately the same mass, but the surface temperature on Venus is far hotter than the hottest regions on earth, and the atmosphere of Venus exerts more than 90 times the pressure exerted by Earth's atmosphere. And Venus is surrounded by clouds loaded with sulfuric acid, clouds so dense that optical telescopes can't penetrate them. Robert?

S: But the textbook goes into a lot of detail about the surface features of Venus, like there are a lot of volcanoes and most of the craters look pretty fresh and stuff like that. P: That's right.

S: How can we know that if we can't see through the clouds? P: Good question. The answer is that the clouds block light waves, but they don't block radar waves. So in the 1990s the United States sent an orbiting space probe to Venus. It was called Magellan. Magellan's mission was to collect radar data and relay them back to Earth, where they were used to create a detailed map of the planet. The European Space Agency did the same thing in 2005 when they sent up a probe called Venus Express, which brings me to my next point.

These probes Magellan and Venus Express mapped the same area. So we should have been able to lay these two maps, one on top of the other, and see the same volcanoes and craters in exactly the same places, even though the information was collected 15 years apart. But that's not what happened when the two maps were compared. The surface features didn't line up, and the explanation researchers arrived at was that the rate of Venus's rotation had changed, that Venus was rotating at a slower rate when Venus Express was in orbit than when Magellan was in orbit.

Now we've already known for some time that Venus rotates very slowly. One day on Venus is equal to eight months on Earth. The academic year at this university runs from September to May. That's about a single day on Venus. Uh, but the discrepancy between these maps suggests that its rotation has slowed even more by six and a half minutes. Okay, granted, there could be something out of whack here. The instruments on either Magellan or Venus Express might have malfunctioned, but long range radar mapping of Venus has also been done from earth based observatories, and it's shown the same result. So what's putting the brakes on Venus, assuming the slowdowns for real，Jennifer？

S: Well, you said it's covered by dense clouds. Could they have something to do with it? P: They could indeed. Not only does Venus have impenetrably dense clouds, it also has powerful winds reaching speeds of more than 200 miles per hour. And the best theory we have right now is that these high intensity weather systems are causing a lot of friction against the planet's surface. Over the long term, that friction is putting the brakes on the planet's rotation.

S: Can the same thing happen here on earth? P: Well, our winds and tides do have some effect on Earth's rotation, but it's minimal, just tiny fractions of a second over long periods of time, nothing like what's apparently happened on Venus. One thing it'd be very helpful to know is whether Venus has a liquid core or a solid core. The type of core would influence how Venus reacts to various external forces, and speaking of Earth, the more we learn about the forces, particularly the atmospheric forces, that have shaped the evolution of Venus, the more insight we'll have into the forces that are currently shaping the evolution of Earth. So we really need to land a probe on the surface.

S: On the surface? P: The Russians did it in the 1970s and 80s. But because of the intense heat and pressure, none of them lasted more than two hours. Of course, the technology's come a long way since then. The thing is, there's only so much funding available for space exploration, and Venus missions are currently not that high on the priority list.