NASA will make the most distant fly-by of any solar system object ever on New Year's Day.
That's when its spacecraft New Horizons will take images of Ultima Thule.
Ultima Thule is about the size of Oakland and San Jose combined.
It's an object that sits in what's called the Kuiper Belt.
"The Kuiper Belt objects formed in the outer part of the solar system - early on - and we think they've mostly been sitting there - in deep freeze - and so we are really excited to see this type of object because it may be a piece of the early solar system we can study," New Horizons Co-Investigator Kelsey Singer said.
Ultima is about a billion miles from Pluto. NASA said it is likely icy with a little bit of rock as well.
Mysterious streak of light seen in sky above California
NASA's New Horizons spacecraft to take pictures of Ultima Thule