The farthest man-made thing

The farthest man-made thing, the Voyager 1 spacecraft, has detected a change in its local environment. At a distance of 85 times the Earth–Sun separation, Voyager first detected a greatly enhanced density of energetic particles that lasted more than six months, from mid-2002 into 2003, then dropped to normal levels. Two research groups have interpreted the data differently. One group believes that Voyager has finally passed through our solar system’s termination shock, the region of space where the outward-going supersonic wind of solar particles brakes to subsonic speeds in its confrontation with the interstellar medium. That group says the shock then overtook the spacecraft again at 87 times the Sun–Earth separation. The shock front is generally expected to be a good particle accelerator, and the observed upswing in fast particles is suggestive. The other group, however, argues that the observed increase was an expected precursor—the accelerated particles streaming back...