A spacecraft that made a historic flyby of Pluto in July has a new destination — an icy rock that may reveal what the outer solar system was like shortly after it formed 4.6 billion years ago.

NASA's New Horizons spacecraft's next target is 2014 MU69 and nicknamed PT 1 or "potential target 1," the U.S. space agency announced Friday afternoon. The mysterious icy object is less than 45 kilometres across — a tiny fraction of the size of Pluto, which is 2,370 kilometres wide. PT 1 is 1.6 billion kilometres farther away than Pluto, which was itself 4.7 billion kilometres from Earth when the spacecraft flew by.

Both Pluto and PT 1 are in an outer region of the solar system known as the Kuiper Belt, which contains thousands of icy objects, some very small and others that are large enough to be considered dwarf planets, such as Pluto.

2019 arrival

New Horizons will begin changing direction to target PT 1 in late October or early November and is expected to arrive on New Year's Day 2019. If all goes well, it will take measurements and detailed images of a type of celestial object that has never been seen before.

"There's so much that we can learn from close-up spacecraft observations that we'll never learn from Earth, as the Pluto flyby demonstrated so spectacularly," said New Horizons science team member John Spencer of the Southwest Research Institute in Boulder, Colo., in a statement. "The detailed images and other data that New Horizons could obtain from a KBO flyby will revolutionize our understanding of the Kuiper Belt and KBOs."

While the spacecraft will soon be headed in the right direction, scientists won't be able to actually study PT 1 unless they get some extra funding, as the New Horizons mission officially ends on Oct. 1, 2016. They will apply for the extra funding early next year.

NASA's New Horizons spacecraft will take this path toward its next potential target, the Kuiper Belt object 2014 MU69, nicknamed PT1 (for Potential Target 1). Also shown are the relative locations of several dwarf planets in the Kuiper Belt. (Alex Parker/Southwest Research Institute/Johns Hopkins University Applied Physics Laboratory/NASA)

Unlike Pluto, which shows signs of geological activity and an actively changing surface with features such as flowing glaciers, PT 1 is thought to have been deep frozen since its formation. Small objects like PT 1 are thought to be the building blocks that formed Kuiper Belt dwarf planets like Pluto.

New Horizons launched in 2006 to explore Pluto and its moons, but the mission team has been looking for another potential destination in the Kuiper Belt since 2011.

PT 1 was one of five discovered using the Hubble Space Telescope in 2014. The list was later narrowed down to two that were close enough to the spacecraft's flight path. Between them, PT 1 was chosen because New Horizons didn't need as much fuel to get there, leaving more fuel for the flyby itself, for scientific measurements, and as a backup in case of unforseen circumstances, said Alan Stern, principal investigator of the New Horizons mission, in a statement.