Juno listens to radio noise triggered by Jupiter’s volcanic moon Io

The Juno Waves instrument “listened” to radio broadcasts from Jupiter’s immense magnetic field to find their precise locations.

Listening to the electron shower pouring down on Jupiter from its intensely volcanic moon Io, researchers using NASA’s Juno spacecraft have discovered what sets off the powerful radio emissions in the monster planet’s gigantic magnetic field. The new result sheds light on the behavior of the huge magnetic fields generated by giant gas planets like Jupiter.

Jupiter has the largest and most powerful magnetic field of all the planets in our solar system, with a force at its source about 20,000 times that of Earth. It is shaken by the solar wind, a flow of electrically charged particles and magnetic fields constantly blowing from the Sun. Depending on the strength of the solar wind, Jupiter’s magnetic field can extend up to 2 million miles (3.2 million kilometers) towards the Sun and extend over 600 million miles (over 965 million kilometers) from the Sun, as far as Saturn’s orbit.

Jupiter has several large moons that orbit its massive magnetic field, with Io being the closest. Io is caught in a gravitational tug-of-war between Jupiter and the two neighbors of these other large moons, which generates internal heat that powers hundreds of volcanic eruptions on its surface.

These volcanoes collectively release a ton of matter (gas and particles) per second into space near Jupiter. Some of this material divides into electrically charged ions and electrons and is quickly captured by Jupiter’s magnetic field. As Jupiter’s magnetic field exceeds Io, the moon’s electrons are accelerated along the magnetic field toward Jupiter’s poles. Along the way, these electrons generate “HF” radio waves (called HF radio broadcasts, or DAMs). The Juno Waves instrument can “listen” to this radio broadcast generated by the electron shower.

The researchers used the Juno wave data to identify the precise locations in Jupiter’s vast magnetic field from which these radio broadcasts originated. These locations are where the conditions are ideal for generating the radio waves; they have the right magnetic field strength and the right electron density (neither too much nor too little), according to the team.

“The radio broadcast is probably constant, but Juno must be in the right place to listen,” said Yasmina Martos of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland, College Park.

Radio waves emerge from the source along the walls of a hollow cone aligned and controlled by the strength and shape of Jupiter’s magnetic field. Juno only receives the signal when Jupiter’s rotation sweeps this cone above the spacecraft, in the same way that a lighthouse beacon briefly lights up a ship at sea. Martos is the lead author of an article on this. research published in June 2020 in the Journal of Geophysical Research: Planets.

Juno’s data allowed the team to calculate that the energy of the electrons generating the radio waves was much higher than expected, up to 23 times higher. Also, electrons don’t necessarily need to come from a volcanic moon. For example, they could be in the planet’s magnetic field (magnetosphere) or originate from the Sun as part of the solar wind, according to the team.