On June 13th, 1983, something extraordinary happened in the cold vacuum of space that nobody had planned for and that would have caused absolute pandemonium had it occurred just a few minutes later. The Pioneer 10 spacecraft, which had already made history as the first human-made object to travel through the asteroid belt and visit Jupiter, crossed the orbit of Neptune and became the most distant human-made object from Earth.

Now, you might be thinking that doesn't sound particularly weird, but here's where it gets deliciously strange. Neptune at that moment was actually closer to the Sun than Pluto due to the odd elliptical nature of Pluto's orbit, a situation that would persist until 1999. So Pioneer 10 hadn't actually left the solar system in any meaningful sense, but it had crossed an invisible line that represented the furthest planetary orbit, even though that planet wasn't actually there at the time.

The spacecraft itself had already stopped taking pictures years earlier. Its camera had been turned off after the Jupiter flyby in 1973 to conserve power, so this momentous occasion passed without so much as a single photograph to commemorate it. Pioneer 10 just kept hurtling through the void in silence, carrying its famous gold-anodized plaque depicting a nude man and woman and a map showing Earth's location, like the universe's most optimistic message in a bottle.

The real kicker is that NASA scientists were tracking this milestone with slide rules and early computers while the spacecraft itself, built with 1970s technology, had no idea it was making history. It simply continued its lonely journey toward the star Aldebaran, which it won't reach for another two million years, give or take a few millennia.