The Scientific Investigations: Fields and Particles

Fields & Particles

 
The spun section contains six instruments that investigate particles and magnetic fields. (An adjunct to the ultraviolet spectrometer—the extreme ultraviolet spectrometer—is also carried on the spinning section.)


Magnetometer
 
This instrument is used to determine the strength and direction of the magnetic field within the magnetosphere.

The magnetometer (MAG) uses two sets of three sensors. One set is located at the end of the magnetometer boom and, in this position, is about 11 meters from the spin axis of the spacecraft. The second set, designed to detect stronger fields, is 6.7 meters from the spin axis. The boom is used to remove the sensors from the immediate vicinity of the spacecraft to minimize magnetic effects from the spacecraft.

However, not all these effects can be eliminated by distancing the instrument. The rotation of the spacecraft is used to separate natural magnetic fields from engineering-induced fields. Another source of potential error in measurement comes from bending and twisting of the long magnetometer boom. To account for these motions, a calibration coil is mounted rigidly on the spacecraft and puts out a reference magnetic field during calibrations.


Plasma Instrument
 
Plasma consists of electrically charged particles—ions, which carry a positive charge, and electrons, which carry a negative charge. Usually, the number of ions in a plasma equals the number of electrons, so the plasma as a whole is electrically neutral, but ions and electrons travel different paths within the magnetosphere. The plasma instrument (PLS) measures the energies and directions of approach of ions and electrons comprising the plasma. PLS also uses a mass spectrometer to identify the composition of the ions.

Information from PLS helps determine the temperature of the plasma and the manner in which the particles are distributed in space. This information in turn helps scientists understand particle dynamics in the magnetosphere, for example, where particles are being lost and where particles are being energized.


Energetic Particles Detector
 
The energetic particles detector (EPD) is designed to measure the ions and electrons with energies greater than those being detected by the Plasma Instrument. The EPD can also measure the direction of travel of such particles and, in the case of ions, can determine their composition (whether the ion is oxygen or sulfur, for example). It will also be able to tell how the particles get their energy and how they are transported through Jupiter’s magnetosphere.


Plasma Wave Subsystem
 
Particles of plasma are bound to the magnetic field. Motions within the plasma can perturb the surrounding magnetic and electric fields: these are called "plasma waves." Some of these waves can cause particles to be lost from the magnetosphere.

Dust Detector Subsystem
 
"Dust" is a term used by astronomers to describe small grains of matter found not only in planetary systems but also in interstellar space, often mixed in with interstellar clouds of gas. Dust can be a natural part of the magnetosphere, or it can come from Jupiter, the satellites, or even from external forces like Comet Shoemaker–Levy 9.

The Dust Detector Subsystem (DDS) will be used to measure the mass, electric charge, and velocity of these minute particles as they are swept into the detector by the motion of Galileo.These studies will help determine dust origin and dynamics within the magnetosphere.


Heavy Ion Counter
 
Besides providing data for the scientists, the heavy ion counter (HIC) experiment will also be used by the engineers.

The engineers will use the HIC to measure and monitor very high-energy heavy ions (such as the nuclei of oxygen atoms) hitting the spacecraft. These measurements provide basic information on a form of radiation that can cause random changes in a spacecraft’s electronics. This type of information could perhaps give clues for the design of better radiation resistant electronics for future missions.

The scientists will also take advantage of the HIC's data. For example, the heavy ion count detected during solar flare activity by previous space missions is used for models of the sun's composition.