It is getting bigger.
Last week, NASA released photos of the New Horizons space exploration vehicle, which is gradually approaching an ancient, little-known object in space called Ultima Thule.
Ultima is orbiting the Sun a billion kilometers beyond Pluto, and NASA expects to crash near the far-flung object shortly after midnight on January 1, 2019.
It will be the furthest encounter of humanity with another world.
"What will Ultima reveal, no one knows," wrote NASA's planetary scientist NASA, who led the space mission, last week.
NASA suspects that Ultima is a type of ice mass formed about 4.5 billion years ago during the formation of our solar system.
But since then, hovering in the freezing cold outer reaches of the solar system, it is believed that Ultima has largely been preserved in its original, primitive state – allowing scientists to see the distant past.
"Ultima should be a valuable window into the early stages of planet formation and what the solar system looked like over 4.5 billion years ago," said Stern Welten, who surrounded the solar system beyond the last great planet Neptune. It is a "region of remnants of the early history of the solar system," says NASA.
Ultima has already proven to be somewhat mysterious.
From earlier images, scientists have learned that Ultima probably has a strange, non-spherical shape. But as New Horizons approaches, the light pattern reflected by Ultima or its light curve is inconsistent. For most other objects, these patterns of light are repeated as the objects rotate.
"It's really a mystery," Stern said in a statement.
Other New Horizons scientists speculated that a cloud of dust or moons that "crashed" around Ultima could create the strange light curve.
But there is one thing is almost certain.
On December 15, Stern's team concluded that there were no obstacles between New Horizons (a triangular spaceship 7 feet long and 9 feet high) and Ultima Thule.
Stern told NASA that the space probe is now "Go" to get closer to Ultima.
In the summer of 2015, New Horizons flew through Pluto. It has captured an unprecedented detail of the dwarf planet, its mountains, cliffs and icy plains. The reconnaissance vessel flew 7000 miles from Pluto's surface.
But it will be much closer to Ultima Thule, plunging 2200 miles over the little-known object.
The first pictures are expected early on New Year's Day, about 30 minutes after the ball fell on Times Square.
"The Ultima Thule flyby will be fast, it will be challenging and it will also give it new knowledge," Stern said.
"The farthest exploration of anything in history will also be historical."
We will watch.
To see the images coming in during Ultima's approach, Join NASA TV's livestream which starts at 12:15. ET, January 1, 2019 .