Properties Determining Eruption Initiation and Planeto-Effectiveness of Eruptive Transients in Magnetically Active Stars
Abstract
We present a combined theoretical and data analysis approach to, first, understand why magnetic eruptions and corresponding ejecta are triggered in strong-field regions of the Sun and magnetically active stars and, second, assess the key physical parameters responsible for the planeto-effectiveness of these eruptions, both on Earth and in other (exo-)planets. This approach converges on one physical parameter besides magnetic energy, at least for stellar coronae of high magnetic Reynolds numbers allowing this parameter to be conserved even under confined energy release: magnetic helicity. Helicity, via the magnetic energy-helicity diagram, should be treated equally with magnetic energy. Due to magnetic helicity accumulation in solar active regions and its inverse cascading, solar - and stellar, correspondingly - eruptions may become inevitable after a certain 'point-of-no-return' is reached. We identify this critical instant as the time when magnetic polarity inversion lines in active-region photospheres accumulate fluxes that generate fields stronger than local equipartition values. Furthermore, using the conserved helicity budgets we abstractly model post-eruption flux ropes and their transit through astrospheres, reaching exoplanets and compressing their magnetospheres via magnetic pressure effects. A rudimentary validation between the near-Sun and L1 axial magnetic field values of these data-constrained flux ropes is encouraging and allows us to further constrain scaling laws appropriate for the astrospheric transit of these ropes. Importantly, we also find that exoplanets orbiting magnetically active dwarf stars at orbital radii that are fractions of an astronomical unit seem to be strong contenders for eruption-driven atmospheric erosion that may gradually even deprive them from their atmospheres. Some famous exoplanet cases are examined under this prism. Future improvements are expected by widely anticipated space- (Parker Solar Probe and Solar Orbiter) and ground-based (Daniel K. Inouye Solar Telescope) observations.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.993G