Japan and the European Space Agency are planning a joint mission that would be the first to land a probe on Mercury, a government official said Wednesday.

The mission entails three probes -- two that would orbit and one that would land -- to map the topography and study the origins of the closest planet to the sun.

Russian Soyuz rockets would launch the probes starting in 2010; the probes would reach Mercury about four years later and spend a year charting the planet.