The Juno Magnetic Field Investigation

Abstract

The Juno Magnetic Field investigation (MAG) characterizes Jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ∼20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno's massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6 × 10 6 nT per axis) with a resolution of ∼0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno's spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft.

The Juno Waves Investigation

“…Source regions will be apparent as emissions at the local electron cyclotron frequency are observed. While in burst mode, Waves will obtain waveforms of the radio emissions in a 1-MHz bandwidth including f ce by using the onboard magnetometer (Connerney et al 2017) measurement of |B| to tune the receiver. Survey measurements will be made at a 1-spectrum/s cadence up to 41 MHz.…”

“…Voyager 1 revealed the existence of lightning at Jupiter Cook et al 1979) through the detection of lightning whistlers in the Io torus. Juno will thread magnetic field lines which pass through latitudes in which lightning has been detected by Voyager and Galileo, typically near ∼ 50 • jovigraphic latitude (Little et al 1999).…”

“…The spectrum analyzer compiles a spectrum from digital spectrum analysis between 100 kHz and 3 MHz and by a swept frequency receiver from 3 to 41 MHz. The waveform receiver can be tuned to a 1-MHz band between 3 and 41 MHz that includes the electron cyclotron frequency f ce derived from onboard fluxgate Magnetometer (MAG) measurements (Connerney et al 2017) and generates waveforms for signals within that band. If f ce is below 3 MHz, then the 100 kHz-3 MHz baseband channel can be selected for waveform measurements.…”

First look at Jupiter's synchrotron emission from Juno's perspective

“…Juno is the first spacecraft to probe the innermost regions of Jupiter's radiation belts with high temporal and spatial resolutions. Our modeling effort of MWR measurements is intimately connected to the success and the timing of other experiments in the Juno mission [see, e.g., Becker et al, 2017a;Connerney et al, 2017;Mauk et al, 2013], in a coupled manner. The assimilation of magnetic and particle data during the Juno mission as well as understanding newly revealed properties (if any) of the radiation belts will be necessary to refine our models of field and particles and subsequently our simulations of synchrotron emission.…”

Planetary Magnetism

“…Juno's mission plan wraps the planet in a net of observations ( Figure 12) provided by 32 near-polar orbits with periapsis just above the cloud tops, uniformly distributed in longitude (separation of 12 ). The Juno magnetic field investigation is designed to map Jupiter's magnetic field with very high accuracy, sufficient to characterize the field to degree and order 12-15, depending on the dynamo core radius (estimated 0.75-0.85R j ) and other assumptions (Connerney et al, 2014).…”