NASA scientists had a reason other than the new year to celebrate Tuesday after receiving confirmation that their New Horizons probe had approached an unknown object in the most far-flung region of our solar system, some four billion miles away from Earth. Confirmation that the craft had reached the so-called "third zone" of the Kuiper Belt came about 10 hours after expected.

New Horizons' Mission Operations Manager (shortened to "Mom") Alice Bowman said, "We have a healthy spacecraft, we have just completed the most distant flyby."

NASA Marks New Year’s With Record-Breaking Fly-By Of Unknown Object, 4 Billion Miles From Earth

Regarding the unknown object, Mission Controller Alan Stern noted that "it's 35x50 km [about 22x31 miles], and it's an irregular shape. It could be bi-lobate, with asymetric lobes, or it could be these are two things in orbit - and tomorrow we will know which is the case."

Because of the distance, Mission Control is observing what happened six hours earlier. "There's a lot of anxious people staring at screens in Mission Control," said Mark Holdridge, the Encounter Mission Manager. An object the size of a grain of rice hitting the craft could destabilize it, as the probe is traveling at 31,500 miles per hour.

NASA Marks New Year’s With Record-Breaking Fly-By Of Unknown Object, 4 Billion Miles From Earth

For the time being, the only images that have come to Earth of the giant, unknown object, named Ultima Thule, are in black and white. Color photos will only be available in the coming days. "We set a record," said Stern. "Never before has a spacecraft explored anything so far away. Think of it. We're a billion miles farther than Pluto."

NASA Marks New Year’s With Record-Breaking Fly-By Of Unknown Object, 4 Billion Miles From Earth

Mankind had no knowledge of Ultima Thule whatsoever until 2014, which was eight years after the New Horizons probe was launched. The Hubble Space Telescope picked up on it, so NASA put it next on the probe's itinerary.

The Kuiper Belt is a frozen expanse beyond the farthest planet from the sun, Neptune. The region where Ultima Thule is located is also known as the Twilight Zone. The mysterious object is believed to be from 4.5 billion years ago when the solar system was formed, so it's "probably the best time capsule we've ever had for understanding the birth of our solar system and the planets in it," said Stern.

NASA Marks New Year’s With Record-breaking Fly-by Of Unknown Object 4 Billion Miles From Earth

It's yet unknown what Ultima Thule's shape is, only that it appears to to be peanut-shaped. It may even be two or more objects.