Magnetosphere
The region of space surrounding Earth dominated by Earth's geomagnetic field, shielding the planet from harmful solar wind plasma.
Governing formula
Magnetopause Distance R_mp ≈ (B₀² / (2 μ₀ ρ v²))^(1/6)
SI unit
Earth Radii (R_E ~ 10 R_E sunward)
In depth
Supersonic solar wind compresses the magnetosphere to ~10 Earth radii on the dayside while stretching it into a long magnetotail (>100 R_E) on the nightside.
Examples in the real world
Van Allen radiation belts trapping high-energy charged protons and electrons within the magnetosphere.