The nerdiest New Year's party in the solar system happened 4 billion miles from Earth, where a lone, intrepid spacecraft just flew past the farthest object humans have ever explored.

There was no champagne in this dim and distant region, where a halo of icy worlds called the Kuiper belt circles the outermost edge of the solar system. There were no renditions of "Auld Lang Syne" (in space, no one can hear you sing).

But there was a minivan-size spacecraft called New Horizons. And there was a puny, primitive object called Ultima Thule, a rocky relic of the solar system's origins, whose name means "beyond the borders of the known world."

At New Horizon's birthplace, the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, scores of space scientists gathered Tuesday morning to wait for the signal confirming that New Horizons had survived its encounter with Ultima Thule.

The call came at 10:31 a.m. Eastern: The spacecraft's systems were working. Its cameras and recorder were pointed in the right direction.

“We have a healthy spacecraft,” mission operations manager Alice Bowman announced. “We have just completed the most distant flyby. We are ready for Ultima Thule science transmission — science to help us understand the origins of our solar system.”

At mission control, and in an APL auditorium where the rest of the science team was watching, people jumped from their seats and broke into cheers. The borders of the known world had just been pushed a little bit farther.

It had been 30 years since the mission to the outer reaches of the solar system was first conceived. Thirteen years since New Horizons launched from Kennedy Space Center, speeding away from Earth faster than any probe had traveled before. Three years since the spacecraft's famous and fateful encounter with Pluto, when it revealed the distant dwarf planet to be a complex and colorful world. And it had been 10 hours since 12:33 a.m., when the spacecraft was supposed to make the closest approach to its target.

"At this moment, while we're speaking, New Horizons is taking its riskiest observation," project scientist Alan Stern said in the early hours of Tuesday morning.

Most other Earthlings had already counted down til midnight and popped their champagne, but at APL, the assembled scientists, their family and friends were still waiting. Way out in the Kuiper belt, they knew, Ultima Thule was growing larger in New Horizon's field of view, glowing like a full moon.

"Thirty seconds to flyby," Stern said. "Are you ready? Are you psyched? Are you jazzed?"

Twenty seconds. Ten. And then Stern raised his hand in the air while confetti fell from the ceiling. The crowd cheered.

"New Horizons is at Ultima Thule," Stern proclaimed.

Or so he hoped. The spacecraft was still too busy conducting observations to send any information home. When it did beam out a status update, the immense distance from Ultima Thule meant it took more than six hours for the light to reach Earth.

The scientists did not know until Tuesday morning whether New Horizons had succeeded. It will take days to resolve the first sharp images, and months for all the data collected during the encounter to finally stream down.

But somewhere out in the dusky, dusty expanse of the Kuiper belt, New Horizons is already speeding further into the distance, Ultima Thule shrinking in the rear view.

This is the biggest and busiest moment for the New Horizons team since its spacecraft soared past Pluto three years ago, capturing detailed close-up photos of the distant dwarf planet.

Helene Winters, the mission's project manager, said spacecraft operators have been subsisting on chocolate and sleeping on air mattresses at the APL so they could make the most of every minute until New Horizons reached its target. Navigators kept a watchful eye out for potential hazards, which can be hard to spot in this faraway corner of the solar system.

Asked whether she thought she would be able to sleep Monday night, Winters laughed. "Ask me again tomorrow."

The following morning, New Horizons's operators sat in mission control, anxious. Data from the Deep Space Network, a chain of radio antennas NASA uses to communicate with distant spacecraft, was displayed on their screens.

Bowman sat with her hands folded, leaning toward her computer.

"In lock with telemetry," Bowman said.

In the APL auditorium, where the rest of the team and their families were watching, the crowd erupted in cheers.

Next came the status check: Planning — nominal. Power — green. Solid state recorders — pointed right where NASA wanted them. The spacecraft was healthy. New Horizons had done it.

Bowman grinned.

It was a fitting end to a celebration that began the night before. The scene at APL was somewhere between a New Year's party, a scientific conference, and a comic book convention. Researchers gave talks about the history of the early solar system. Scientists and their guests munched on crudités in a room lit with sparkling blue lights. Small children up long past their bedtimes scurried between chairs and sneaked cookies from the buffet.

"This is like a dream come true," said Chuck Fields, a podcast producer from Indianapolis who drove nine hours to attend Monday's event. He was dressed in a blindingly bright blazer and tie bearing images of planets, galaxies and the sun. His wife, Dawn, wore matching pants.

"You can find anything on Amazon," Dawn said with a laugh.

"Alan (Stern) said this was going to be a celebration," Chuck added. "So it was like, okay, let's celebrate!"

Benjamin Holder, 5, pored over an image of New Horizons and the distant rock it was due to encounter.

"I used to have a cat named Toolie," Benjamin said. "But the Thule rock that you're looking for is not named after my cat."

His uncle, Erik Lessac-Chenen, stifled a laugh. As a member of the spacecraft's optical-navigation team, he had devoted the better part of the past year and a half to tracking down that "Thule rock."

NASA nodded to the (entirely coincidental) timing of the encounter by counting down to 12 a.m. and distributing plastic cups of champagne. Then astrophysicist Brian May, better known as lead guitarist for the rock band Queen, debuted a song he wrote for the occasion.

"I'm not nervous," Stern said, with minutes to go until the encounter. "No, no, no. We'll find out how it all went in the morning."

New Horizons is the first NASA mission designed specifically to explore the outer solar system — a region that Stern calls "a scientific wonderland." Out in the Kuiper belt, where sunlight is 0.05 percent as strong as it is on Earth and temperatures hover close to absolute zero, the primitive building blocks of planets have persisted unchanged for 4.6 billion years.

"This is history-making, what we're doing, in more ways than one," Stern said. Every image sent back from New Horizons is the most distant photograph ever taken. Each maneuver is further than anything NASA has done before.

Ultima Thule is also among the most primitive objects ever explored. Unlike planets, which are transformed by geologic forces in their interiors, and asteroids, which are heated by the sun, Ultima Thule is thought to have existed in a "deep freeze" since it first formed.

"It is probably the best time capsule we've ever had for understanding the birth of our solar system and the planets in it," Stern said.

The encounter with Ultima Thule is among the more difficult feats NASA has attempted. The great distances from Earth and the sun mean that scientists must put up with a long communications lag, and instruments must operate with very little light. Ultima Thule was discovered four years ago, and its orbit and surroundings still aren't well known. And New Horizons is a 13-year-old vehicle; its power generator produces just a quarter as much wattage as a lightbulb, which means operators must carefully prioritize their use of remaining fuel.

The sheer speeds and distances involved boggle the mind. Ultima Thule is 1 percent the size of Pluto, and New Horizons must get four times closer to image it. At the moment of closest approach, the spacecraft was moving at a breathtaking 32,000 miles per hour. Its cameras had to swivel to track Ultima Thule as it passed by; otherwise, all it would see is a blur amid the black.

The New Horizons team had several experiments planned for the brief encounter. Particle and dust detectors were programmed to probe the environment around Ultima Thule. The spacecraft's three cameras took images in color and black and white in an effort to map the tiny world and determine its composition.

Deputy project scientist John Spencer said Monday that he is especially interested in those detailed color photos, which could illuminate a "particular mystery" about "cold classical" Kuiper belt objects such as Ultima Thule, which never underwent dramatic geologic change. Although these rocks should be primarily made of ice, they appear reddish when viewed through the Hubble Space Telescope. It may be that the ices contain impurities that change color when struck by cosmic rays, Spencer said — a possibility he hopes to pin down by looking into craters of more recently exposed material.

"Who knows?" he said. "Anything is possible when you're exploring a new class of world you've never seen before."

The moment also involved an unprecedented radio science experiment. Six hours before the moment of closest approach, the dishes of the Deep Space Network — which NASA uses to communicate with far-flung spacecraft — blasted a powerful radio signal in Ultima Thule's direction. The signal was timed to arrive at the rock at the same time New Horizons does on Jan. 1, allowing the spacecraft to study how those radio waves get reflected off its surface.

As APL staff began to set out plastic cups for champagne Monday night, those signals were racing toward their rendezvous with New Horizons and Ultima Thule — a message from an old year on this world, to the next year on a new one.