WATCH: NASA says faraway world Ultima Thule shaped like 'snowman'

Ultima Thule, an icy celestial body that NASA scientists announced on Wednesday is aptly shaped like a giant snowman and orbits over six billion kilometres from the sun.

The first detailed images beamed back from the US agency's New Horizons mission allowed scientists to confidently determine the body was formed when two spheres, or "lobes", slowly gravitated toward each other until they stuck together - a major scientific discovery.

The New Horizons spacecraft on Tuesday flew past Ultima Thule, which was discovered via telescope in 2014 and is the farthest and potentially oldest cosmic body ever observed by a spacecraft.

Before that flyby, the only image scientists had was a blurry one showing Ultima Thule's oblong shape, resembling something like a bowling pin or a peanut.

"That image is so 2018... Meet Ultima Thule!" said lead investigator Alan Stern, doing little to hide his joy as he revealed a new sharper image of the cosmic body, taken at a distance as close as 27 000km with a resolution of 140 metres per pixel.

"That bowling pin is gone - it's a snowman if anything at all," Stern said during a NASA briefing.

"What this spacecraft and this team accomplished is unprecedented."

This image made available by NASA shows images wit

This image made available by NASA shows images with separate color and detail information, and a composited image of both, showing Ultima Thule. (NASA via AP)

Ultima Thule's surface reflects light about as much as "garden variety dirt", he said, as the sun's rays are 1 600 times fainter there than on Earth.

The body is roughly 30.5km long and completes its own rotation in about 15 hours. NASA dubbed the larger lobe Ultima, and the other, which is about three times smaller, Thule.

Carly Howett, another researcher of the mission, noted: "We can definitely say that Ultima Thule is red," perhaps due to irradiation of ice.

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