The flyby is expected to happen at 12:33 a.m. ET on January 1.
Called a "relic" of the early Solar System, Ultima Thule is estimated to be anywhere from 25 to 45 kilometers in diameter, but astronomers will have a much better idea of its size and shape once New Horizons makes its close pass.
Until then, the New Horizons spacecraft continues speeding through space at 32,000 miles (51,500 kilometers) per hour, traveling nearly a million miles per day.
The Kuiper Belt lies in the so-called "third zone" of our solar system, beyond the terrestrial planets (inner zone) and gas giants (middle zone). The spacecraft is now travelling through space at 32,000 miles per hour so it will be impossible to turn the spacecraft around in case of a mistake.
NASA's New Horizons spacecraft launched on its initial mission to Pluto in 2006, making a flyby of the dwarf planet on July 14, 2015. In temperatures that cold, the rocks have essentially been frozen in time for billions of years. That is why New Horizon's flyby is very important for NASA.
The object was previously known as 2014 MU69.
Thule was a mythical island on medieval maps, thought to be the most northern point on Earth.
"It's very hard, we don't have much information about (Ultima Thule)", Pelletier said in a recent interview with The Canadian Press. Travelling beyond Pluto wasn't the primary mission of the New Horizons spacecraft, so over the past 3 ½ years, the NASA team has been able to program and change the course of the spacecraft in order to make this possible. "Our spacecraft is heading beyond the limits of the known worlds, to what will be this mission's next achievement".
As we approach the probe's arrival at Ultima Thule, NASA is announcing its schedule of events related to the probe's flyby.
Once the flyby happens and mission scientists understand more about just what Ultima Thule is, NASA will choose a formal name to submit to the International Astronomical Union. Ultima Thule might help scientists to study the formation history of our solar system.
"At 32,000 miles an hour, if we hit something as small as a rice pellet, it would destroy the spacecraft - that would be the equivalent of hitting a Mack truck on the highway", Stern said. Also, the fact that Ultima Thule will become the first ever Kuiper Belt object to be studied leaves enough room (and hope) that great surprises will be uncovered. In 2017, scientists determined that it isn't spherical, but more elongated. With the wildly successful flyby behind them, mission planners won an extension from NASA and set their sights on a destination deep inside the Kuiper Belt. Compensating for that somewhat is that the dim sunlight in the Kuiper Belt left it past the "snow line" for a variety of gasses, meaning those gasses froze out to form particles.
"We expect to have an image with nearly 10,000 pixels on Ultima ready for release on January 2", Dr Stern said.