From Solar Orbiter to PLATO: Monitoring Global Solar Activity to Understand Cool Stars Magnetism

The magnetic activity of cool stars, like the Sun, is driven by the interplay of rotation and convection that fuels dynamo-action in their interiors. At the surface, dynamo-generated magnetic fields emerge as "spots" (or active regions) that shape the circumstellar environment via winds, radiation, and transient events like flares and coronal mass ejections (collectively “space weather”). Stellar magnetism erodes the atmospheres of exoplanets and obscures smaller Earth-like exoplanets from detection. The Sun has a well-known 11-year activity cycle where spot emergence drifts from mid to low latitudes. The appearance of spots in close proximity to one another, referred to as nesting, affects up to 50% of emergences and creates long-lived sources of magnetic activity (called active nests). Nesting appears to be an innate feature stellar dynamos since it has also been observed on other Sun-like stars. It is theorized that non-axisymmetries in the generation and storage of the magnetic field form active nests at specific latitudes and longitudes. This phenomenon has consequences for forecasting solar activity and understanding the dynamo mechanism operating in other cool stars. Studies of solar active nests have been limited by our single viewpoint from Earth. With ESA’s Solar Orbiter providing observations of the Sun's far-side for several months each year, we now have a global view of solar magnetism. As solar activity increased in 2022, we identified an active nest that was responsible for 50–70% of all solar flares over the entire solar surface for five months (a prolific flare factory). During solar maximum in 2024, we surveilled two prolific active nests that later collided, triggering an intensification of flaring activity. These continuous, multi-viewpoint observations allow us to assess the Sun’s global activity and start to make connections with the nesting on other low-mass stars; a link that will be further explored with ESA’s PLATO mission.