It was also the first space probe to send back information on interstellar space which remains very impressive for a craft built with the best tech of the early Seventies. It was only designed to get the scoop on Jupiter but I think NASA got it to hang in there to confirm some data on Uranus, Neptune and Pluto (no longer a planet).
When I was in grade school there was a piece on In the News between CBS’s Saturday morning cartoons about Pioneer 9 and 10 being set up to for one last duty. Some object was messing with the astronomers’ data on Pluto’s orbit or whatnot. As the two probes exited our solar system, they would help confirm the existence of a possible tenth planet or worse, a black hole not visible to earth-based telescopes (Hubble was 10-plus years away). Being a kid, the latter prospect sounded horrifying thanks to Sci-Fi movies. By high school, I was in an Astronomy class and there was no mention of either possibility. Heck, 10‘s exit wasn’t even mentioned along with the Kuiper Belt, which was probably the culprit or Pluto’s three probable moons. I do recall the Oort Cloud which used to be the only source of comets until Kuiper was added to the equation.
January 22, 2003 was the last signal Earth received. The transmission was rather faint and lacked accurate telemetry (position, velocity, etc.) because its power source had been too depleted to tell us.
Currently, 10 is on its way to the Taurus constellation with a gold-anodized plaque showing the location of our system, the probe’s flight and what humans look like. The artwork designed by Dr. Carl Sagan received a lot of grief since the people were naked. Hey, he at least had the foresight not go with contemporary fashions. Intelligent life would avoid us if they learned there was an alien world populated by creatures wearing bell bottoms.