Autonomous mobile robots have become a key technology for unmanned planetary missions. To cope with the rough terrain encountered on most of the planets of interest, new locomotion concepts for rovers and micro-rovers have to be developed and investigated. The most advanced locomotion concepts are based on wheels or caterpillars (e.g. Sojourner (NASA) or Nanokhod (ESA)). These rovers have clear advantages regarding power efficiency and complexity if compared with walking robots. However, they still have quite limited climbing abilities. Typically they can only overcome obstacle of their wheel size. In our paper we present an innovative rover concept with 6 motorized wheels. Using a rhombus configuration, the rover has a steering wheel in the front and the rear, and two wheels arranged on a bogie on each side. The front wheel has a spring suspension to guarantee optimal ground contact of all wheels at any time. The steering of the rover is realized by synchronizing the steering of the front and rear wheels and the speed difference of the bogie wheels. This allows for high precision maneuvers and even turning on the spot with minimum slip. The use of parallel articulations for the front wheel and the bogies enables to set a virtual center of rotation at the level of the wheel axis. This insures maximum stability and climbing abilities even for very low friction coefficients between the wheel and the ground. A well functioning prototype has been designed and manufactured by us. It shows excellent performance surpassing our expectations. This rover is able to passively overcome unstructured obstacles of up to two times its wheel diameter.