NASA's New Horizons approaches Pluto, sending space nerds into orbit

Pluto, get ready for your close-up.

NASA’s New Horizons spacecraft is set to pass within 7,767 miles of the dwarf planet system on Tuesday morning, nine and a half years and roughly 3 billion miles since its launch from Earth.

At a speed of 36,000 mph, the thousand-pound spacecraft — which is the size of a baby grand piano — will also come within 17,931 miles of Charon, Pluto’s jumbo moon.

“We’re going to knock your socks off,” Alan Stern, the mission’s principal scientist, told the Associated Press.

The $723 million mission, Stern said, is nearly “unprecedented.”

According to NBC News, more than 1,000 journalists and VIPs will be in attendance at Johns Hopkins University Applied Physics Laboratory for a Pluto watch party.

Among them: Annette Tombaugh-Sitze, whose late father, Clyde Tombaugh, discovered Pluto in 1930.

“I think my dad would be thrilled with the New Horizons," Tombaugh-Sitze said in a NASA intrview posted online. “When he looked at Pluto, it was just a speck of light.”

Her father's ashes are flying aboard the spacecraft.

The last time a NASA spacecraft unveiled images of the planet was in 1989, when the Voyager 2 swept by Neptune. And Tuesday’s fly-by falls on the 50th anniversary of the Mariner 4’s trip to Mars.

“It’s the first time in 25 years that we’ve approached an unknown world of this size,” New Horizons scientist John Spencer told Mashable.

Not surprisingly, "Plutophiles" are agog.

"This is it — this is our once-in-a-lifetime opportunity to see it," Hal Weaver, a scientist at Johns Hopkins, told the AP.

Weaver says images of Pluto captured by New Horizons in recent weeks have whet the appetite for space nerds like him.

"The science team is just drooling over these pictures," Weaver said.

In June, the New Horizons spacecraft spotted "a strange dark patch" at the pole of Charon, piquing the team's interest even more.

"Every terrain type we see on the planet — including both the brightest and darkest surface areas — are represented there," Stern told Space.com. "It’s a wonderland!"

So how big is Pluto?

With a diameter of 1,430 miles, Pluto is just two-thirds the size of the Earth's moon. But Pluto boasts its own mini solar system that includes Charon and four "baby moons": Styx, Nix, Hydra and Kerberos.

What exactly is there?

No one knows for sure, but despite temperatures that can plunge to nearly minus-400 degrees, the New Horizons team expects to see remnants of volcanic activity — possibly more — on Pluto.

"Anybody who thinks that when we go to Pluto, we're going to find cold, dead ice balls is in for a rude shock," Bill McKinnon, a New Horizons team member from Washington University, told AP. "I'm really hoping to see a very active and dynamic world."

Wait, isn't Pluto technically *not* a planet?

Correct. In August 2006 — seven months after the New Horizons launch — the International Astronomical Union voted to demote Pluto from "major planet" to "dwarf planet." Just don't tell that to Stern.

"Anything that's big enough to be round, we call a planet, as long as it's not a star," he told Mashable.

When does this happen again?

New Horizons makes its historic fly-by Tuesday at 7:49 a.m. EDT, but images of Pluto's closest close-ups aren't expected until Wednesday. And scientists say all of the data from the New Horizons mission won't be transmitted until October 2016.

For a mission that's taken nearly a decade, what's another 16 months between planets?

As Cathy Olkin, New Horizons deputy project scientist, put it: "We're all going to have to be patient."