NASA is about to explore Ultima Thule — the farthest object humanity has ever tried to visit. Here's what to expect from the 'mind-boggling' encounter 4 billion miles from Earth.

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NASA's New Horizons probe, which visited Pluto in 2015, is closing in on a mysterious object called Ultima Thule.
New Horizons will fly past Ultima Thule, formally known as 2014 MU₆₉, on New Year's Day.
Ultima Thule will be the most distant object humanity has ever visited (if the flyby goes as planned).
The nuclear-powered spacecraft will take hundreds photos of the space rock.
The flyby is "about 10,000 times" more challenging than visiting Pluto, the mission's leader said.

NASA scientists are about to make history by flying a probe past a mysterious, mountain-size object beyond the orbit of Pluto.

The object is called Ultima Thule (pronounced "tool-ee"), and it's more than 4 billion miles from Earth. If the flyby goes as planned, this will be the most distant object humanity has ever tried to explore.

NASA's nuclear-powered New Horizons spacecraft will attempt the maneuver on New Year's Day, taking hundreds of photos in a highly choreographed, pre-programmed sequence. The space probe will reach its closest point to the space rock — about 2,175 miles — at 12:33 a.m. EST. New Horizons will also turn around to photograph its exit at a speed of 35,000 mph.

The mission is as surprising as it is ambitious: NASA didn't know Ultima Thule — or 2014 MU₆₉, as it's formally known — existed when New Horizons launched toward Pluto in 2006. There wasn't even a reliable way to detect the object until astronauts plugged an upgraded camera into the Hubble Space Telescope in 2009.

The uncertainty about Ultima Thule makes planetary science researchers like Alan Stern, who leads the New Horizons mission, all the more excited about the flyby.

"If we knew what to expect, we wouldn't be going to Ultima Thule. It's an object we’ve never encountered before," Stern told Business Insider. "This is what what exploration is about."

Here's what to expect from the flyby and how to watch a live broadcast.

What Ultima Thule is and where it's located

kuiper belt objects kbos pluto new horizons flight path ultima thule 2014 mu69 alex parker jhuapl swri

New Horizons is coasting through a zone called the Kuiper Belt, a region where sunlight is about as weak as the light from a full moon on Earth. That far away, frozen leftovers of the solar system's formation — called Kuiper Belt Objects, or KBOs — lurk in vast numbers (Pluto is one).

Ultima Thule is one of these pristine remnants. It has presumably remained in its distant and icy orbit for billions of years, and it's too small to be a planet (so its early history hasn't been hidden by its own mass).

Studying the object might therefore reveal new clues about how the solar system evolved to form planets like Earth, Stern said.

"Ultima is the first thing we've been to that is not big enough to have a geological engine like a planet, and also something that's never been warmed greatly by the sun," he said. "It's like a time capsule from 4.5 billion years ago. That's what makes it so special."

Stern compared the flyby to an archaeological dig in Egypt.

"It's like the first time someone opened up the pharaoh's tomb and went inside, and you see what the culture was like 1,000 years ago," he said. "Except this is exploring the dawn of the solar system."

Stern considers Ultima Thule to be a "planetesimal" or seed that might have formed a planet if it had acquired enough material.

"It's a building block of larger planets, or a planetary embryo," Stern said. "In that sense, it's like a paleontologist finding the fossilized embryo of a dinosaur. It has a very special value."

Journey into the unknown

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Before flying toward Ultima Thule, New Horizons performed the first-ever visit to Pluto in 2015.

In June, New Horizons woke up from half a year of hibernation to begin zeroing in on this new target. Mission managers then fired the probe's engine in October to put it on a more precise path to Ultima Thule. Last week, researchers finished confirming that there are no obvious moons, debris fields, or other objects floating in the flight path of New Horizons, so they kept the robot on-course for its historic encounter.

Stern said the initial images that New Horizons captures will each take two hours to transmit. Then each bit of image data, moving at the speed of light as radio waves, will take about six hours to reach antennas on Earth. Those early photos will be released to the public on January 2.

However, those images will be small (as they were for Pluto). It will take months to receive the most detailed, full-resolution images due to the power, antenna, and other physical limitations of the New Horizons spacecraft. The first full-resolution images won't arrive until February. And it could take two years for the researchers to get all of the data.

Stern shied away from making any predictions about what the images might show, citing how shocking the first close-up pictures of Pluto were.

"I don't know what we're going to find," he said. "If it's anything as surprising as Pluto, though, it will be wonderful."

Once scientists are finally able to pore over New Horizons' images of Ultima Thule, they will pay close attention to the outward appearance of the rock. Learning whether the surface is relatively smooth or features a mix of pebbles, huge boulders, cliffs, and other features will yield clues about how planets form.

'10,000 times harder than reaching Pluto'

Stern, who recently helped write a book titled "Chasing New Horizons: Inside the Epic First Mission to Pluto," said Ultima Thule got its name from a Norse phrase that means "beyond the farthest frontiers."

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Hubble first definitively photographed Ultima Thule in June 2014, which was about a year before New Horizons visited Pluto.

This upcoming flyby is far more difficult than the Pluto visit, Stern said.

"Rendezvousing with something the size of a large, filthy mountain covered in dirt, a billion miles away from Pluto, and honing in on it is about 10,000 times harder than reaching Pluto," he said. "That's because it's about 10,000 times smaller. The achievement of getting to it is unbelievable."

In a New York Times op-ed published on New Year's Eve, Stern described the mission as "mind-boggling."

"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," Stern wrote.

The target of New Horizons' cameras and other instruments won't just be Ultima Thule itself, either.

"We're plastering all of the space around it for moons, rings, and even an atmosphere," Stern said. "If any of those things are there, we'll see them."

Watch live coverage of New Horizons' flyby of Ultima Thule

New Horizons control room

Anyone interested in watching Ultima Thule flyby events can tune into several live video broadcasts being hosted on New Year's Eve and New Year's Day. Broadcasts that feature the first images and science results will occur later, on Wednesday and Thursday.

Johns Hopkins University's Applied Physical Laboratory (JHU APL), which manages the New Horizons mission, will host the suite of broadcasts through the lab's YouTube channel.

Additionally, NASA TV and NASA Live will mirror some of the New Horizons coverage, even though the government shutdown — led by President Donald Trump over border-wall funding — has sent many NASA workers home.

The first Ultima Thule broadcast will be a press conference with Stern and other mission scientists on Monday at 2 p.m. EST. Then, at 12:02 a.m. on Tuesday, Queen guitarist and astrophysicist Brain May will release a song dedicated to the mission. Video coverage will continue through 12:15 a.m. EST — the moment New Horizons flies past Ultima Thule about 4 billion miles from Earth.

Michael Buckley, a JHU APL spokesperson, said there will be a video feed of the moment scientists learn that the mission succeeded. That live coverage should begin on Tuesday around 9:30 a.m. EST, and the "ok" signal from New Horizons should arrive around 10 a.m. EST. A press conference will follow at 11:30 a.m. EST.

On Wednesday at 2 p.m. EST and Thursday at the same time, JHU APL will host follow-up press conferences to discuss new photos and scientific results.

You can watch the main New Horizons events via the NASA Live video player we've embedded below.