Voyager 1 took this photo of Jupiter and two of its satellites (Io, left, and Europa) on Feb. 13, 1979. Io is about 220,000 miles above Jupiter's Great Red Spot; Europa is about 375,000 miles ...

A twin probe, Voyager 2, saw the same thing in 2007. Last year, Voyager 1 witnessed another exit sign. The number of cosmic rays from interstellar space went up, perhaps because the Sun’s ...