Strong hydromagnetic turbulence associated with comet Giacobini‐Zinner

The turbulence surrounding comet Giacobini‐Zinner reached intensities three orders of magnitudes above that of “intermediate” solar wind conditions, was characterized by Δ B/B o almost equal to one, and extended to cometocentric distances beyond 10 6 km. The strong spectral peak at f ∼ 10 −2 Hz and the general intensity profile of the turbulence (a lack of emissions close to the nucleus [< 2.5 × 10 4 km], peak intensities near the bow wave, and a spatial extend > 10 6 km) are in excellent agreement with generation by plasma instabilities associated with the pickup of H 2 O + group ions. The total energy of the magnetic turbulence near f ∼ 10 −2 Hz is estimated to be ∼ 5 × 10 15 joules and that of ion energization due to solar wind pickup ∼6 × 10 13 watts. It thus takes a minimum of ∼ 100 s to build up the magnetic turbulence. This scale is approximately the linear growth rate of the ion pickup instability, giving a consistent picture of the energy source of the turbulence.