The power of electromagnetic chorus radio waves are a million times more intense near the Jovian moon Ganymede, and 100 times more intense near the moon Europa than the average around these planets. These are the new results from a systematic study on Jupiter’s wave environment taken from the Galileo Probe spacecraft.
Chorus waves are a special type of radio wave occurring at very low frequencies. Unlike the Earth, Ganymede and Europa orbit inside the giant magnetic field of Jupiter. It is believed Jupiter’s giant magnetic field is one of the key factors powering the waves. Jupiter’s magnetic field is the largest in the solar system, and some 20,000 times stronger than the Earth’s.
“Chorus waves have been detected in space around the Earth but they are nowhere near as strong as the waves at Jupiter” says Professor Richard Horne of British Antarctic Survey who is a co-author on the study. “Even if small portion of these waves escapes the immediate vicinity of Ganymede, they will be capable of accelerating particles to very high energies and ultimately producing very fast electrons inside Jupiter’s magnetic field”.
At the Earth, chorus waves play a major role in producing high-energy ‘killer’ electrons that can damage spacecraft. The new observations raise the question as to whether they can do the same at Jupiter.
Observations of Jupiter’s waves provides us unique opportunity to understand the fundamental processes that are relevant to laboratory plasmas and the quest for new energy sources, and processes of acceleration and loss around the planets in the solar system and in the distant corners of the Universe. Similar processes may occur in exoplanets orbiting other stars and the understanding obtained in this study may help us detect whether exoplanets have magnetic fields. This study will provide very important observational constraints for theoretical studies that will try to quantify the tremendous increase in wave power.
Understanding of wave environments is critical for the understanding of how particles are accelerated and lost in space. This study shows that in the vicinity of Europa and Ganymede, that respectively have induced and internal magnetic fields, chorus wave power is significantly increased. The observed enhancements are persistent and exceed median values of wave activity by up to 6 orders of magnitude for Ganymede. Produced waves may have a pronounced effect on the acceleration and loss of particles in the Jovian magnetosphere and other astrophysical objects. The generated waves are capable of significantly modifying the energetic particle environment, accelerating particles to very high energies, or producing depletions in phase space density. Observations of Jupiter’s magnetosphere provide a unique opportunity to observe how objects with an internal magnetic field can interact with particles trapped in magnetic fields of larger scale objects.
If the waves escape the moons’ magnetosphere, the moons may have a pronounced effect on the radiation environment of Jupiter’s magnetosphere which may in turn affect the particle environment through wave–particle interactions. Even though the increase in wave power cannot be seen outside of ~2 moon radii, waves may be efficiently accelerating particles that are later transported radially. The increase in wave intensity that we observe may be already moderated by the wave–particle energy exchange. In other words, by the time waves are observed, they may have already given a significant portion of energy to the charged particles. These waves may allow the transport of energy from low energy and low pitch angles that are lost to Ganymede’s loss cone, and generate waves that will accelerate high energy particles.