Voyager 1 at the Galaxy's Edge
Based on data gathered by the Low-Energy Charged Particle (LECP) instrument on NASA's Voyager 1 spacecraft, this figure shows that high-speed (near the speed of light) particles called cosmic rays, originating in the galaxy, are not isotropic — that is, they do not arrive with the same intensity from all directions. The green and red points are cosmic rays moving in the direction perpendicular to the radial direction from the sun and are relatively flat. The black points, however, show large changes and represent particles moving away from and toward the sun. They also happen to be moving perpendicular to the magnetic field, shown by the red line in the pie plot at lower right. If Voyager 1 was free of the sun's influence, all points would fall on the same, flat line.
The measurents are obtained by rotating the detector platform of LECP (inset picture) through eight, 45-degree sectors depicted by the the flywheel inset on the upper left. The stepper motor underneath the platform steps once every 192 seconds; it was tested for 500,000 steps, enough for four years of Voyager's initial mission to Jupiter and Saturn, but has now exceeded 6 million steps over 35-plus years.
Image Credit: NASA/JPL-Caltech/Johns Hopkins University Applied Physics Laboratory
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