On this day in 1977, Voyager 2—the space probe that indirectly made me a scientist—launched. Despite being the second Voyager probe, it actually launched before Voyager 1. This was due to their differing missions: Voyager 2 took a slower, longer course to visit the four giant planets, while Voyager 1 headed at a faster clip, visiting only Jupiter and Saturn. Voyager 2 is the longest-operating NASA spacecraft, an impressive achievement of engineering and science.

I’ve written on several occasions how images from Voyager 2 first made me aware of other worlds—Jupiter, Saturn, Uranus, Neptune, and their moons—as real places. Today, even with my (somewhat) greater scientific knowledge compared to my young self, I still am impressed with the Voyager missions. Even now, I’m in love with the images, though of course that wasn’t the primary purpose of the Voyager program. The plasma and charged-particle detectors, ultraviolet and radio instruments, and magnetic field analyzers on the probes provided incredible information about the outer planets and their moons. Earth’s magnetic poles aren’t exactly at the North and South geographic poles, but they’re relatively close; Voyager 2 discovered the magnetic fields of Uranus and Neptune are highly displaced from their poles. Voyager 1 found the volcanoes on Io and first measured Titan’s atmosphere—leading to the Huygens Titan lander 20 years later.

Now the Voyagers are poised at the probable edge of the Solar System: the heliosheath. The remaining active instruments aboard the Voyager craft are measuring an increased number of charged particles, which the Sun’s magnetic field deflects from the Solar System. While several quasi-premature announcements have been made about the probes’ departure from the Solar System, it will happen—making them the first true deep-space probes. When you consider they store their data on an 8-track tape, that’s pretty good.