For most people following the New Horizons spacecraft, the mission to fly past Pluto has been a celebration of human exploration. For Annette and Alden Tombaugh, the event is also a memorial.

Their father, Clyde Tombaugh, is the man credited with putting Pluto on the map of the solar system. His ashes were put in a two-inch aluminum capsule onboard the New Horizons spacecraft, which was expected to have flown past Pluto early Tuesday morning.

On the capsule was inscribed the words: “Interned herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system’s ‘third zone.’ Adelle and Muron’s boy, Patricia’s husband, Annette and Alden’s father, astronomer, teacher, punster, and friend: Clyde Tombaugh (1906-1997).”

It's no surprise that the children of the man who first identified the speck of light in the sky as a planet — at least that's what it was classified to be in 1930 — grew up surrounded by astronomy. On vacations, leg room in the car was often sacrificed for telescopes. Annette and Alden — and many of their children — have asteroids discovered by their father named after them.

"(Astronomy) was something that was ingrained in us," Alden said. "He would drag us to the telescope and we would say, 'Oh yeah...'"

The two came to the Johns Hopkins Applied Physics Lab Tuesday along with other relatives to celebrate as their father's ashes flew beyond Pluto into the Kuiper Belt, making him the farthest traveling person in history. His wife, Patricia, missed the event by only three years, having died at the age of 100 in 2012.

Annette attributes her existence to her father's discovery of Pluto. It was his breakthrough that got him a scholarship to attend the University of Kansas, which led him to meet her mother.

"We are really children of Pluto," she said.

Clyde Tombaugh discovered the icy world of Pluto as an amateur astronomer working as a researcher for the Lowell Observatory in Flagstaff, Ariz., after its existence had been predicted as "Planet X" by Percival Lowell and William Pickering.

He took photos of the missing planet with a photographic telescope, but that's a far-flung difference from the high-definition photographs that are just now emerging from the New Horizons mission. By Wednesday, New Horizon's cameras will have taken photos with enough resolution to identify the ponds in Central Park had it been flying past Earth, scientists at the APL said.

"He would have said it looks like Mars," Annette said. "I love the heart on it — it's a nice touch."

However, Clyde probably would have felt uncomfortable around the massive international media frenzy surrounding the event. He was described as a shy man who shunned the limelight as much as possible. Annette said he had declined to appear with Johnny Carson — a sort of amateur astronomer — on The Tonight Show multiple times.

"Teaching was dad's thing," Alden said. "Being in front of a classroom is where he liked to be ... He inspired a lot of people."

Of course, Clyde's children are fierce advocates that Pluto's classification as a dwarf planet is wrong.

"If it were up to me, we would have a model with ten planets, including Ceres," she said.

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