InterHelios-Sun and Mercury Observer

Abstract The rationale and scientific objectives for a new mission, the InterHelios or Sun and Mercury Observer mission, its ballistic design and orbital characteristics are presented. This mission will provide observations of the Sun and solar wind from almost heliosynchronous orbits within heliocentric distances from about 30 to 40 R s . The second target will be Mercury, its surface and its gas and plasma environment. During the multiple fly-bys, Mercury's surface features, the tenuous exosphere and highly dynamic magnetosphere will be studied. The in-situ-wind and remote-solar measurements will permit us to determine the characteristics of the wind and associated plasma and magnetic fields in the regions of the heliosphere that are related with the magnetically active streamer belt and coronal holes extending to near-ecliptic latitudes. The high-resolution imaging and spectroscopic measurements will enable us to understand better the time-variability and fine-scale structure of the solar source regions of the transient slow solar wind, and the underlying heating processes in the chromosphere and corona.