For about three hours on Wednesday, Voyager 1 had left the solar system — before a rewritten news release headline pulled it back in. Voyager 1, one of two spacecraft NASA launched in 1977 on a grand tour of the outer planets, is now nearly 18.5 billion kilometres from the sun, speeding away at 61,000 kilometres per hour.
In a paper accepted by the journal Geophysical Review Letters, William R. Webber of New Mexico State University and Frank B. McDonald of the University of Maryland reported that on Aug. 25 last year, the spacecraft observed a sudden change in the mix of cosmic rays hitting it.
Cosmic rays are high-speed charged particles, mostly protons. Voyager 1’s instruments recorded nearly a doubling of cosmic rays from outside the solar system, while the intensity of cosmic rays that had been trapped in the outer solar system dropped by 90%.
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