It has taken nearly a decade and 3 billion miles to get there, but scientists are about to get their first look at Pluto.
The New Horizons spacecraft is closing fast on the tiny world once thought to be at the edge of our solar system. On Tuesday the probe will begin an intensive nine-day scientific study of Pluto and its moons.
It has been a long time coming. New Horizons was launched in 2006. The spacecraft, roughly the size of a baby grand piano, rode atop a massive rocket that hurled it away from Earth faster than any spacecraft before it.
Today it's so far away that it takes hours for its radio signal to reach Earth.
"From Earth to Pluto, where our spacecraft is, is going to be about 4 1/2 hours," says Alice Bowman, the Mission Operations Manager of New Horizons. "So the information that we're receiving right now was sent 4 1/2 hours earlier."
And it takes another 4 1/2 hours to send commands back. The people in mission control can't do things in real time.
"No operator can sit on Earth and use a joystick to control where the spacecraft is looking or taking observations," Bowman says. "Pretty much you have to make a very smart spacecraft."
New Horizons is going too fast to stop at Pluto. So it has just one chance to see the icy world as it whizzes by. Scientists like Bowman are doing everything they can to make sure the brief encounter goes smoothly.
There's a lot at stake. The spacecraft is programmed to make over a thousand different scientific observations in the next nine days, according to Alan Stern, New Horizon's principal investigator.
Stern says what planetary scientists know about Pluto right now could probably fit on a single sheet of paper.
It's comparatively small, he says. "If you drove around its equator, it's about like clocking the distance from Manhattan all the way to Maui in Hawaii." It has five moons that we know of. The biggest one, Charon, is the size of Texas.
But maybe the most important thing about Pluto is that we now know it is part of a vast outer region of our solar system called the Kuiper Belt.
The belt "contains a very large number — probably billions — of comets," Stern says. "And it also contains thousands of little worldlets."
Those worldlets are smaller than Pluto, but there are plenty of Pluto-sized planets, too.
"There are more of them than there are gas giants and rocky planets," he says.
This is a first look at a mysterious world in an unexplored part of our solar system, and Stern says there's never going to be another mission like it.
DAVID GREENE, HOST:
Back in 2006, a powerful rocket lifted off from Florida.
(SOUNDBITE OF ROCKET LAUNCH)
UNIDENTIFIED MAN: Ignition and lift-off of NASA's New Horizons spacecraft.
UNIDENTIFIED PEOPLE: (Cheering).
GREENE: And onboard was a spacecraft about the size of a baby grand piano. The rocket flung it towards the cold dwarf planet Pluto. Tomorrow, nine-and-a-half years after its journey began, the spacecraft will begin to study Pluto up close. NPR's Geoff Brumfiel reports on this long and extraordinary trip.
GEOFF BRUMFIEL, BYLINE: The day I visited the control room of NASA's New Horizons mission, two young guys were manning the computers. Their boss, Alice Bowman, told me they were still in school when it launched. Now she says...
ALICE BOWMAN: They probably are five or so years out of college.
BRUMFIEL: You're letting two guys in their 20s - they are completely in charge of America's only mission to Pluto?
BOWMAN: They're part of the team. I would say that they cannot send anything to the spacecraft without me signing off on it.
BRUMFIEL: The New Horizons spacecraft is now nearly 3 billion miles from Earth. That's so far way it takes a while to phone home.
BOWMAN: So the information that we're receiving from the spacecraft right now was sent four-and-a-half hours earlier.
BRUMFIEL: And it takes another four-and-a-half hours to send commands back. The people in mission control can't do things in real time.
BOWMAN: No operator can sit on earth and use a joystick to control where the spacecraft is looking or taking observations. Pretty much, you have to make a very smart spacecraft.
BRUMFIEL: New Horizons is going too fast to stop at Pluto, so it will have just one chance to see the icy world as it whizzes by. Scientists like Bowman are doing everything they can to make sure the brief encounter goes smoothly.
BOWMAN: What's coming down today is observations that are looking for any kind of hazard along our path.
BRUMFIEL: Like what?
BOWMAN: Maybe undiscovered moons.
BRUMFIEL: That's right. They're worried the spacecraft could smack into a moon no one's ever seen before. That's how uncharted Pluto is.
ALAN STERN: Let me tell you what we know about Pluto. We could probably put it on one piece of paper.
BRUMFIEL: Alan Stern is the principal investigator for the New Horizons mission. Pluto's not too big.
STERN: If you drove around its equator, it's about like clocking the distance from Manhattan all the way west to Maui in Hawaii.
BRUMFIEL: It has five moons that we know of. The biggest one, Charon, is the size of Texas.
STERN: The other ones range from more like Vermont down to literally Manhattan Island.
BRUMFIEL: Scientists think Pluto itself has a rocky core surrounded by ice. But maybe the most important thing about it is that we now know Pluto is not alone. It's part of a vast outer region of the solar system called the Kuiper Belt.
STERN: It contains a very large number - probably billions - of comets. And it also contains thousands of little worldlets.
BRUMFIEL: Those worldlets are smaller than Pluto, but there are plenty of Pluto-sized planets, too.
STERN: There are more of them than there are gas giants and rocky planets in by the sun combined.
BRUMFIEL: This is a first look at a mysterious world in an unexplored part of our solar system. Stern says there's just not going to be another mission like it.
STERN: No space agency on earth is planning to do another first mission to a brand-new planet anywhere in the solar system. So it really is a unique 21st-century event.
BRUMFIEL: The full encounter starts tomorrow, but it will reach its climax in a week, when the spacecraft swoops past Pluto's surface. Scientists hope it will send home lots of cool pictures of this unexplored, icy world. Geoff Brumfiel, NPR news. Transcript provided by NPR, Copyright NPR.