Magnetic Waves Excited by Newborn Pickup H+Near Jupiter: Neutral Hydrogen Loss by the Planetary System

We report here observations of magnetic waves recorded by the Voyager spacecraft in the solar wind near Jupiter that are possibly the result of excitation by newborn pickup H+. Consideration of growth rates due to the known interstellar ion sources strongly disfavor an interstellar source. To determine the likely source of the waves, we compute the minimum ion production rate by equating wave growth to turbulent cascade rates and derive a lower limit for the production of H+at the times of observations. The only available source of neutral H at these times and at the levels required is the Jovian system, most notably charge exchange between energetic protons and the neutral clouds around Io and Europa's orbits. Further refinement of the source identity is not possible at this time. We provide an estimate for the neutral H source subject to assumptions of the latitudinal extent of the population which is not constrained by observation. The Voyager spacecraft instruments include a fluxgate magnetometer called MAG that measures the changing ambient magnetic field. We report observations by MAG of low‐frequency waves in the solar wind outside the Jovian magnetosphere that are seen at frequencies and with characteristics that suggest the waves are excited by protons that originate as neutral hydrogen. Collision with solar wind protons ionize the neutral hydrogen to produce an energetic ion population called pickup ions. We use known characteristics of wave excitation by pickup ions to estimate the rate of pickup ion production. The only source that is strong enough to produce the pickup ions with the number density required is the Jovian system. Magnetic waves were measured by Voyagers 1 and 2 in the solar wind near the magnetosphere of JupiterThese waves have signatures of excitation by local pickup H+ionsA neutral H loss rate of ∼5 × 1028s−1from the Jovian system is estimated Magnetic waves were measured by Voyagers 1 and 2 in the solar wind near the magnetosphere of Jupiter These waves have signatures of excitation by local pickup H+ions A neutral H loss rate of ∼5 × 1028s−1from the Jovian system is estimated