CRSCosmic Ray SubsystemEnergetic nuclei and electrons in cosmic raysswitched offactiveStatus verified 2026-08-11
Science instruments
The original experiments studied planets, fields, particles and plasma. Only a few low-power instruments continue today; the table does not imply automatic synchronisation.
LECPLow-Energy Charged ParticlesLower-energy ions, electrons and cosmic raysswitched offhistorically completedMAGMagnetometerMagnetic-field strength and directionactiveactivePWSPlasma Wave SubsystemElectron plasma waves and plasma densityactiveactivePLSPlasma ScienceProperties of low-energy plasma particlesfailedswitched offISSImaging Science SubsystemWide-angle and narrow-angle planetary imaginghistorically completedhistorically completedIRISInfrared Interferometer SpectrometerAtmospheric composition and thermal balancehistorically completedhistorically completedPPSPhotopolarimeter SubsystemPolarisation and structure of atmospheres and ringsfailedfailedPRAPlanetary Radio AstronomyPlanetary radio emissionshistorically completedhistorically completedUVSUltraviolet SpectrometerUltraviolet spectra of atmospheres and interplanetary spaceswitched offswitched offActive on 11 August 2026: Voyager 1 — MAG, PWS; Voyager 2 — CRS, MAG, PWS. Sources: current NASA announcements and the spacecraft design page.
Statuses distinguish active instruments, intentionally switched-off instruments, historically completed experiments and technical failures. The reason and date are available in each badge’s description.
From scientific question to measurement
What the instruments reveal about Voyager's surroundings
Each device captures a different property of the environment. The resulting image is created by the joint reading of measurements of the magnetic field, particles and plasma. The four examples below explain the principles and demonstrate results; the operating status of individual probes is dated in the table above.
How strong is the field and where does it go?
The magnetometer measures the magnetic field along the path of the probe. During planetary flybys, he studied the fields of the giant planets and their interactions with the moons and the solar wind. In interplanetary and interstellar environments, it tracks field changes with space and time.
For Voyager 1, the field strength increased in 2012, but its direction changed little. Therefore, the expected reversal of direction alone did not provide confirmation of the boundary. Scientists had to add other kinds of measurements.
Verified on 2 October 2026: NASA — Voyager Spacecraft · JPL — How Do We Know When Voyager Reaches Interstellar Space?.
What can be learned from plasma oscillations?
PWS records electrical waves in plasma. The electron density can be determined from the frequency of local plasma oscillations. In 2013, thanks to these oscillations, Voyager 1 was able to detect denser interstellar plasma.
The team subsequently found weaker oscillations in the autumn 2012 records as well and linked them to particle changes measured as they crossed the heliopause. The analysis of PWS thus completed the evidence that was missing without a functional PLS.
Verified on 2 October 2026: JPL — How Do We Know When Voyager Reaches Interstellar Space?.
How is the cosmic ray population changing?
CRS detects very energetic particles. Detectors make it possible to measure their energies and distinguish the composition of the nuclei. The scientific goal is also to observe how particles spread through different regions of space.
As Voyager 2 left the heliosphere in 2018, galactic cosmic rays increased and particles associated with the heliosphere decreased. This documented transition is one example of how the numbers of detected particles help determine the nature of the surrounding environment.
Verified on 2 October 2026: NASA — Voyager Spacecraft · JPL — NASA's Voyager 2 Probe Enters Interstellar Space.
How does the solar wind flow?
PLS measures the low-energy ions and electrons that make up plasma. Its properties, such as density, temperature and flow speed, are determined from the measured currents.
On November 5, 2018, Voyager 2's PLS detected a sharp change in the solar wind. Subsequent measurements no longer showed its original flow. This historic result helped confirm the probe's entry into interstellar space.
Verified on 2 October 2026: NASA — Voyager Spacecraft · JPL — NASA's Voyager 2 Probe Enters Interstellar Space.
Why are the measurements read together
Crossing the heliopause is a conclusion from multiple observations. Particle detectors, magnetometer and plasma measurements complement each other. In addition, Voyager 1 and Voyager 2 did not have the same set of functional instruments available, so the method of obtaining the decisive evidence also differed.
Details follow the articles about heliosphere, cosmic rays a plasma wave recording.
Verified on 2 October 2026: JPL — How Do We Know When Voyager Reaches Interstellar Space? · JPL — NASA's Voyager 2 Probe Enters Interstellar Space.