The craft — one of twin spacecraft sent to explore distant planets — is approaching interstellar space.
Voyager I, an unmanned craft which has traveled about 18 billion miles from the sun since its launch on Sept. 5, 1977, turns 35 on Wednesday. (Its twin spacecraft, Voyager 2, celebrated its 35th on Aug. 20.) Voyager 1 was originally sent to observe Saturn and Jupiter, and is now approaching the fringes of the solar system. NASA via AP Buy Photo