Spacecraft sees slowing of Venus rotation PARIS, Feb. 10 (UPI) -- A spacecraft orbiting Venus has discovered the cloud-covered planet is rotating a little slower that previously measured, European Space Agency officials said. An instrument on ESA's Venus Express spacecraft used infrared wavelengths to penetrate the thick shroud of clouds covering the entire planet and found surface features were displaced by up to 12 miles from where they should be given the accepted rotation rate as measured by NASA's Magellan orbiter in the early 1990s. The Magellan mission determined the length of the day on Venus as being equal to 243.0185 Earth days. However, surface features seen by Venus Express some 16 years later could only be lined up with those observed by Magellan if the length of the Venus day is on average 6.5 minutes longer than Magellan measured, an ESA release said Friday. "When the two maps did not align, I first thought there was a mistake in my calculations as Magellan measured the value very accurately, but we have checked every possible error we could think of," Nils Muller, a planetary scientist at the DLR German Aerospace Centre, said. It is thought the planet's dense atmosphere -- more than 90 times the pressure of Earth's -- and high-speed weather systems may be changing the planet's rotation rate through friction with the surface.