Pluto's discoverer's ashes will be the first human remains to leave the solar system - glued to the side of a space probe

NASA's New Horizons spacecraft is just days out from its historic flyby of Pluto, and it's carrying something oddly poetic on board.

Astronomer Clyde Tombaugh discovered Pluto in 1930. When he died 67 years later, he requested his ashes be sent to space. And he got his wish when New Horizons launched in 2006.

NASA officials attached a small container of a portion of Tombaugh's ashes to the upper deck of the spacecraft. There's an inscription on the container that reads: "Interned herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system's 'third zone.'"

Tombaugh was a Kansas farm boy turned astronomer. He never had the opportunity to go to college, but he built his own telescopes out of old farming equipment and glass.

He got so good at building telescopes that he was able to start observing planets. He wrote to Lowell Observatory for advice on how to build better telescopes.

He sent them some of his Mars, Jupiter, and Saturn drawings. They sent him back a job application.

Not long after starting at Lowell, Tombaugh discovered Pluto.

"For a minute he was the only one who knew there was another planet out there," Annette Tombaugh, his daughter, said in a NASA video about the discovery.

And now part of Tombaugh is on its way to visit the very dwarf planet that made him famous.

"My dad would have been thrilled," Alden Tombaugh, Clyde Tombaugh's son, told NBC News. "He always said that if he had the chance, he wanted to visit the planets. And a little part of him is going to get to do that."

After the Pluto flyby, the probe will continue out into the Kuiper belt and out of the solar system - making Tombaugh's remains the first humans' to ever leave it.