Topographic maps from Magellan and Venus Express clearly show the shift in surface features. At infrared wavelengths Venus Express was able to peer through the dense atmosphere and map surface features observed from both Earth-based radar imaging and with the Russian Venera 15 and 16 missions as well as NASA’s Magellan spacecraft. By comparing the currently accepted rotation rate value for the planet from the Magellan mission, scientists discovered a ‘shift’ in surface features of up to 20 km caused by what they believe is a change in the rotation rate of the planet.