Invited Talk - Plenary
Solar Orbiter and other missions exploring the Sun
Max Planck Institute for Solar System Research
Solar Orbiter is a space mission by ESA and NASA to understand how the Sun creates and controls the Heliosphere and why solar activity changes with time. It combines instruments to measure the plasma and the magnetic field in-situ in the solar wind and to conduct remote-sensing observations. The latter give access to surface magnetic fields, provide information on the dynamics and heating of the plasma in the outer atmosphere, and (indirectly) allow to study to the structure and flows in the solar interior. On its course around the Sun, Solar Orbiter gets as close to the Sun as 0.28 astronomical units which provides observations of the solar corona at an unprecedented spatial resolution of only 200 km. In combination with the in-situ instruments we can understand the magnetic connection from the surface all the way to the heliosphere. The Parker Solar Probe of NASA has an even more extreme orbit than Solar Orbiter, getting as close as only 10 solar radii. The price to pay for this close proximity is that direct observations of the solar disk through remote sensing are no longer possible. However, the in-situ instruments provide an unprecedented sampling of the plasma and the magnetic field deep in the outer atmosphere. Solar Orbiter and Parker Solar Probe are highly complementary and numerous collaborative science programs have been carried out already. The two science results from these two missions that stick out most are probably the magnetic switchbacks and campfires. Switchbacks have been first found by Parker Solar Probe as small-scale reversals of the magnetic field in the outermost corona that might be one of the keys to understand the origin and transport of energy to accelerate the solar wind. Solar Orbiter now provides evidence that these switchbacks originates from small-scale magneto-convection at the solar surface. The campfires are tiny transient brightenings of million Kelvin hot plasma at the base of the solar corona and have been the first big discovery of Solar Orbiter. They might play a key role for the heating of coronal plasma, one of the long-standing problems in stellar astrophysics. These two and other early results give a glimpse of what we can expect in the coming years. This will be of interest not only for our own star, the Sun, but also for other cool stars that might host planets orbiting around them.