Solar Orbiter top science questions: #1 What drives the solar wind and where does the coronal magnetic field originate from?
Non-stop streams of electrons and ions pour from the Sun in all directions, in slow and fast electric wind streams travelling at speeds of 300 to 800 kilometres per second. This solar wind and its variations have a profound effect on the Earth's space environment, as investigated by the Cluster and Double Star missions.
At large scales, the structure of the solar wind and heliospheric magnetic field and their mapping to the solar corona are reasonably well understood. The origin of the slow solar wind, however, is not yet clear, and the mechanisms that heat the corona and accelerate the solar wind remain a mystery. To understand the effects of the Sun on the heliosphere, we need to understand the physics which connects the plasma at the solar surface and the heating and acceleration of the escaping solar wind. This will improve understanding in the future of how stars in general lose mass and angular momentum to stellar winds.
Moving relatively slowly over the solar surface near perihelion, Solar Orbiter will measure how the properties of the solar wind vary, depending on the changing properties of its source region. The results should help distinguish between competing models of solar wind generation. It will be possible to reconstruct the coronal magnetic field by extrapolation, with well-defined boundary conditions, using the photospheric magnetic field measurements, together with those made in situ.