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Pluto may no longer be a planet, as far as Neil deGrasse Tyson is concerned — but it's still pretty cool.

The New Horizons mission to visit the dwarf planet is "a triumph of engineering and the laws of physics," the famed astrophysicist told NBC Nightly News anchor Lester Holt on Tuesday, comparing the feat to "threading a needle from New York to Los Angeles."

NASA's New Horizons probe flew past Pluto on Tuesday morning, completing a 3 billion-mile journey that began more than nine years ago. The spacecraft already has sent back the most detailed images of the dwarf planet ever recorded. The mission team is now waiting for signals from New Horizons to reach Earth on Tuesday night to confirm the probe completed its journey.

Read More: Pluto Flyby! Get In on the Climax of New Horizons

Despite challenges from other scientists, Tyson, who serves as director of the Hayden Planetarium and hosts "StarTalk" on the National Geographic Channel, insists that Pluto is not a planet.

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Instead, it should be called a "dwarf planet," according to Tyson and the International Astronomical Union, because its gravitational influence isn't strong enough to clear other objects out of the neighborhood of its orbit.

Just because it orbits the sun, like Earth, doesn't mean that Pluto is a planet. "Yes, it revolves around the same sun, but while it does that it crosses the orbit of Neptune for 20 years out of its 248-year orbit," he told NBC Nightly News.

"No other planet does that. It's embarrassing," he joked.

Pluto is also really small — new data from New Horizons puts its diameter at 2,370 kilometers (1,473 miles). Tyson referred to Pluto and its moon, Charon, as a "double dwarf planet system": Charon and Pluto are close enough in mass that they circle a center of gravity situated between the two bodies — an arrangement that Tyson likened to a "cosmic ballet."

Read more: Five Things We Just Found Out About Pluto and Charon

Although he has qualms about Pluto's planethood, Tyson is pumped up about the images coming in from New Horizons.

"I feel the excitement because it is an object in our distant backyard that we have never seen up close before," Tyson said. "I’d be excited about that no matter what the object is."

And Tyson couldn't resist sharing at least one mind-blowing fact about Pluto.

"It was discovered in 1930," he said. "You do the math — it’s only completed about a third of its orbit since it was discovered. It hasn’t even made one full trip around the sun."