An asteroid belt mission is being studied by Swedish space authorities in cooperation with Russian, European, and American partners. The mission will perform a survey of the inner solar system with an emphasis on cosmogonic issues, i.e. it will study the importance of plasma processes in the formation and evolution of the solar system. For this purpose the asteroid belt will be visited several times to enable close studies of these primordial bodies, and their interaction with the solar wind. Cosmogony issues to be studied include detailed measurements of the solar wind aberration and its relation to plasma angular momentum transfer, electric current structures in interplanetary space and near small bodies, surface properties of asteroids, and interaction between the heliosphere and interstellar neutrals. Selection of asteroids to be visited will be done so that a variety of taxonomic types, shapes and sizes can be studied. A comet flyby during the mission may also be performed. The mission will carry charged particle and field instruments, a neutral particle imager, a dust/micrometeroid detector, and planetology instrumentation (including infrared and visible imagers) to fully investigate these processes which may shed light on the question of how the solar system has evolved. The mission calls for a small autonomous spacecraft with high reliability and an advanced payload. The platform concept studied has a dry mass of 150 kg, and a payload mass of 44 kg. Hannes is being studied with a planned launch in mid 2002 with Venus and Earth gravity assist maneuvers before the first asteroid encounter in early 2004. The mission is named after the late Nobel laureate Hannes Alfvén.