TAMPA, United States — NASA counted down Monday to a historic flyby of the farthest, and quite possibly the oldest, cosmic body ever explored by humankind — a tiny, distant world called Ultima Thule — in the hopes of learning more about how planets took shape.

The US space agency planned to ring in the New Year with a live online broadcast to mark the spacecraft’s zoom past the mysterious object located about four billion miles (6.4 billion kilometers) away in a dark and frigid region of space known as the Kuiper Belt.

The flyby at 12:33 am Tuesday (0533 GMT) will take place about a billion miles beyond Pluto, which was until now the most faraway world ever visited up close by a spacecraft.

Real-time video of the actual flyby is impossible, since it takes more than six hours for a signal sent from Earth to reach the spaceship, named New Horizons, and another six hours for the response to arrive.

A solo track recorded by legendary Queen guitarist Brian May — who also holds an advanced degree in astrophysics — was set to be released just after midnight to accompany a video simulation as NASA commentators describe the close pass.

The live broadcast can be followed at www.nasa.gov/nasalive.

Hurtling through space at a speed of 32,000 miles per hour, the spacecraft aims to make its closest approach within 2,200 miles of the surface of Ultima Thule.

Alan Stern, the lead planetary scientist on the New Horizons mission, told reporters that Ultima Thule is unique because it is a relic from the early days of the solar system and could provide answers about the origins of other planets.

“The object is in such a deep freeze that it is perfectly preserved from its original formation,” he said.

“Everything we are going to learn about Ultima — from its composition to its geology to how it was originally assembled, whether it has satellites and an atmosphere and those kinds of things — are going to teach us about the original formation conditions of objects in the solar system.”

But the encounter itself is risky, and if the spacecraft were to collide with a speck of space debris as small as a grain of rice, it could be destroyed instantly, mission managers warned.

For that reason, Stern said he and his colleagues are “on pins and needles to see how this turns out.”

The first signal back to Earth should come about 10 hours after the flyby, around 9:45 am (1445 GMT). Only then will NASA know if New Horizons survived the close pass.

Scientists are not sure what Ultima Thule (pronounced TOO-lee) looks like — whether it is cratered or smooth, or even if it is a single object or a cluster.

It was discovered in 2014 with the help of the Hubble Space Telescope, and is believed to be 12-20 miles in size.

A blurred and pixelated image released Monday, taken from 1.2 million miles away, has intrigued scientists because it appears to show an elongated blob, not a round space rock.

Even clearer images should be in hand over the next three days.

Scientists decided to study it with New Horizons after the spaceship, which launched in 2006, completed its main mission of flying by Pluto in 2015, returning the most detailed images ever taken of the dwarf planet.

Seven instruments on board will record high-resolution images and gather data about its size and composition.

The flyby will be fast, at a speed of nine miles per second.

Stern said the goal is to take images of Ultima that are three times the resolution the team had for Pluto.

Ultima Thule is named for a mythical, far-northern island in medieval literature and cartography, according to NASA.

“Ultima Thule means ‘beyond Thule’ — beyond the borders of the known world — symbolizing the exploration of the distant Kuiper Belt and Kuiper Belt objects that New Horizons is performing, something never before done,” the US space agency said in a statement.

According to project scientist Hal Weaver of the Johns Hopkins Applied Physics Laboratory, humans didn’t even know the Kuiper Belt — a vast ring of relics from the formation days of the solar system — existed until the 1990s.

“This is the frontier of planetary science,” said Weaver.

“We finally have reached the outskirts of the solar system, these things that have been there since the beginning and have hardly changed — we think. We will find out.”

In an editorial in The New York Times, Stern recalled that December 2018 marks the 50th anniversary of the first time humans ever explored another world, when US astronauts orbited the Moon aboard Apollo 8.

“New Horizons will continue in that legacy,” Stern wrote.

“As you celebrate New Year’s Day, cast an eye upward and think for a moment about the amazing things our country and our species can do when we set our minds to it.”