It is located in the Kuiper Belt, a huge asteroid belt that surrounds our solar system and contains the leftovers of the system's formation. Officially known as 2014 MU69, it got the nickname Ultima Thule in an online vote.
For just a moment, the craft will fly within 2,200 miles (3,540 km) of Ultima Thule, a primitive space rock from the Kuiper Belt far beyond Neptune.
But New Horizons will finally fly by its target just after midnight on January 1, taking close-up photographs and sophisticated scientific measurements of what it sees.
To the ancient Roman and Greeks, Ultima Thule was originally the most northerly part of the Earth, but the name was used to refer to anywhere which was outside the known world.
EVER, " tweeted the project's lead scientist, Alan Stern of the Southwest Research Institute. "We'll find out Tuesday".
The encounter with Ultima is among the more hard feats NASA has attempted.
As the clock strikes midnight on the east coast of the United States, you can tune in to NASA TV to join the space agency at mission control in the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, as the world celebrates the arrival of New Horizons at Ultima Thule.
New Horizons can't talk to Earth and point to take observations at the same time, and so only after a post-flyby signal is received can the team really relax and begin to anticipate the scientific bonanza heading their way.
NASA's vaunted social media operation, which had fallen silent during the partial government shutdown, has been temporarily restored to cover the event. The flyby will be covered on the lab's website, its YouTube channel and NASA TV. But as of Tuesday morning, New Horizons scientists were betting on a single object. Then the spacecraft was to turn briefly toward Earth to transmit word of its success. Many have likely remained the same since the dawn of the solar system, making them essentially time capsules for astronomers.
'Because of where it was formed and the fact that Ultima is not large enough to have a geologic engine like Pluto and larger planets, we expect that Ultima is the most well-preserved sample of a planetary building block ever explored.
In July of 2015, after travelling for over nine years in space, the New Horizons probe made history, by giving us our very first close-up look at Pluto and its moons. "We're a billion miles further than Pluto, and now we're going to keep going into the Kuiper Belt".
Until the 1990s, no one knew what hid out here, where sunlight is 0.05 as faint as it is on Earth.
These bodies are time capsules, preserved in a deep freeze for the past 4.6 billion years.
But the new target is so far away and so faint that NASA's Hubble Space Telescope was the only instrument that could see it.
A contact binary object is when two large objects - asteroids or comets - orbit each other so closely that they touch. The space rock features a diameter of roughly 19 miles. In this case, the probe will literally sweep past Ultima Thule at a speed of 32,000 miles per hour (51,000 kilometers per hour or about 14.6 kilometers per second).
Although the image provided a new look at Ultima Thule, it lacks detail.
Guests cheer as the New Horizons team members receive signals from the spacecraft that it is healthy. "We are straining at the capabilities of this spacecraft".
"This is just a first glimpse of what is rapidly going to get better from here on out, " Spencer said.