The Radio & Plasma Wave Investigation (RPWI) instrument on the ESA JUICE spacecraft has successfully deployed all its sensors.

The Radio & Plasma Wave Investigation (RPWI) instrument on the ESA JUpiter ICy moons Explorer (JUICE) spacecraft has successfully deployed all its sensors and is now delivering science data.

The RPWI instrument, a European multinational collaboration together with Japan, is led by researchers at the Swedish Institute of Physics (IRF) in Uppsala. RPWI has three unique sets of sensors for measuring the physical properties of the ionized gas (space plasma) surrounding Jupiter and its icy Galilean moon, electric and magnetic field variations, and radio waves. One set constitutes four Langmuir probes (LP-PWI), mounted on 3-metre-long deployable booms. Another set consists of the Radio Wave Instrument (RWI), with three crossed 2.5-meter-long antennas. And the third set is the 3-axial search coil magnetometer (SCM), mounted at 8.2m distance from the spacecraft on the 10.6-metre-long JUICE magnetometer boom.

The LP-PWI booms and RWI antennas were all successfully deployed last week, following the Search Coil Magnetometer (SCM) which successfully started its operations during the deployment of the J-MAG magnetometer boom about one month ago. All sensors deliver science data to the RPWI onboard data processing unit (DPU) before it is sent back to Earth. After seeing the last LP-PWI boom deployed successfully last Friday, the RPWI Principal Investigator, Jan-Erik Wahlund at IRFU exclaimed: “Fantastic, after more than ten years of intensive work, we are finally ready for science discoveries!”.

The DC vector electric field measurements by LP-PWI will be the first ever at Jupiter. These electric field measurements will be sensitive enough to detect the very weak electromagnetic signals from tides and currents within the sub-surface oceans; and near the icy moons themselves.

The RPWI instrument will also for the first time combine three-dimensional measurements of fluctuating electric fields, by LP-PWI, with the full vector measurements of magnetic field fluctuations, by the combined SCM and Low Frequency (LF) receiver. This will provide us with unprecedented opportunities to fully determine the polarization and propagation properties of electromagnetic waves at audible frequencies and to track them to their sources, something which is not possible with data from other past and current missions at Jupiter. This will give novel information on how energy and momentum are transferred between the Icy Moons – Ganymede, Callisto and Europa – and the immense, rotating Jovian magnetosphere allowing for understanding of how plasma is energized. Of particular importance are waves in the vicinity of Ganymede, which is the only natural satellite of the Solar System having its own magnetic field and will be extensively studied by JUICE being the first spacecraft ever orbiting a satellite other than the Moon. This transfer drives, among other processes, the aurora on Ganymede and it may even affect the possibilities of life in the oceans beneath the icy moons’ frozen ice sheets. The moon-magnetosphere coupling, in turn, also strongly affects the conditions in the upper atmosphere of Jupiter.

The suite of RPWI sensors complement each other and have overlapping frequency ranges, from DC up to 45 MHz. Together the sensors are capable of measuring three-dimensional (3D) electromagnetic fields. “Our 3D design strategy makes it possible to measure true physical observables, such as energy and momentum, in Emmy Noether’s sense, without resorting to theories or simulations to interpret the data”, says Jan Bergman, who is a researcher at IRF and Technical Manager for RPWI.

The high-frequency radio observations with RWI will perform unique remote observations using radio signals and their occultations and reflections. The RWI observations will allow us to characterise Jovian radio sources, conduct radio sounding of the ionospheres, and do passive radar measurements of the sub-surfaces of the three icy moons. We also expect to find episodic plume ejections triggered by crustal activities.

The RPWI instrument will perform many scientific measurements during the almost 8-year long cruise en-route to Jupiter. Careful calibration measurements in known environments, like the solar wind, will be made during the long journey to Jupiter. Our mascot, Sonic the Hedgehog, will then be very well trained to detect the tiniest electromagnetic wiggle when we arrive in 2031!

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