Now, it can be shown that in the motion of gyrating particles, the "magnetic moment" μ = W ⊥ /B (or relativistically, p ⊥ /2mγB) stays very nearly constant. The "very nearly" qualifier sets it apart from true constants of motion, such as energy, reducing it to merely an "adiabatic invariant." For most plasmas in the magnetosphere, the deviation from constancy is negligible.