NASA's New Horizons spacecraft flew past a bowling-pin shaped rock in the early hours of new year's day.

The Ultima Thule is located in the Kuiper Belt, a region of objects that could hold the keys to understanding the origins of the solar system.

The object is located beyond Pluto and is the most distant ever visited by a spacecraft.

Signals confirmed the spacecraft had filled its digital recorders with science data on Ultima Thule.

Information reached the mission operations centre at the Johns Hopkins Applied Physics Laboratory in Maryland almost exactly 10 hours after the craft's closest approach to the object.

NASA Administrator Jim Bridenstine said: "Congratulations to NASA's New Horizons team, Johns Hopkins Applied Physics Laboratory and the Southwest Research Institute for making history yet again.

A composite of two images taken by New Horizons' high-resolution Long-Range Reconnaissance Imager (LORRI), which provides the best indication of Ultima Thule's size and shape so far | Image: NASA/JHUAPL/SwRI; sketch courtesy of James Tuttle Keane

"In addition to being the first to explore Pluto, today New Horizons flew by the most distant object ever visited by a spacecraft and became the first to directly explore an object that holds remnants from the birth of our solar system.

"This is what leadership in space exploration is all about."

Images taken during the spacecraft's approach, which brought New Horizons to within just 2,200 miles (3,500 kilometers) of Ultima, revealed it may have a shape similar to a bowling pin, spinning end over end, with dimensions of approximately 20 by 10 miles (32 by 16 kilometers).

Another possibility is Ultima could be two objects orbiting each other.

Flyby data has already solved one of the mysteries, showing that the Kuiper Belt object is spinning like a propeller with the axis pointing approximately toward New Horizons.

NASA said this explains why, in earlier images taken before Ultima was resolved, its brightness did not appear to vary as it rotated.

However the rotation period has not been determined.

The New Horizons spacecraft will continue downloading images and other data in the days and months ahead, completing the return of all science data over the next 20 months.