SP4 – Stars

The young (up to a few 100 Myr) Sun's environment was completely different from the relatively benign conditions in the present solar system. Although the Zero-Age Main Sequence Sun was 30% fainter than at present, its strongly enhanced magnetic activity generated flares, high-energy radiation, coronal mass ejections, high-energy particle beams and shock waves hundreds to thousands of times more intense and frequent than at present. Such extreme conditions cannot have been without consequences for the young solar system and the habitability of Earth-like planets or planetary moons. High-energy radiation and particle flows are key agents for heating and ionization of gaseous surface layers of protoplanetary disks and upper planetary atmospheres; they are therefore principal drivers of chemical reaction networks and therefore of the production of important chemical compounds (water, organics, pre-biotic molecules etc); heating and ionization drives erosion processes in protoplanetary disks (disk evaporation) and planetary atmospheres (evaporation, sputtering, water dissociation, etc.).

Our project is concerned with systematically addressing the star's pivotal role in making its environment habitable, focusing on a detailed understanding of stellar radiation, winds, and particles anchored in stellar magnetic activity. We will focus on star/planet and star/disk systems on which model hypotheses will be tested through observations (e.g., planet-transit systems). Specifically, we will study

  1. the origin, strength, and distribution of magnetic fields on young stars (including T Tauri stars) as a function of age, mass and spectral type from M dwarfs (and brown dwarfs) to A stars, and extrapolation of surface fields to understand their influence on the stellar environment;
  2. ionized-wind expansion out to the planetary environments, based on the distribution of surface magnetic fields;
  3. direct detection of stellar ionized winds or derivation of stringent upper limits;
  4. the evolution of high-energy photons and particles around young stars, especially related to flares and mass ejections, to infer their crucial influence on planetary atmospheres; and
  5. planetary plasma and radiation environments as deduced from transit observations.