Six billion kilometres from the sun floats Ultima Thule, an icy celestial body that scientists announced on Wednesday is aptly shaped like a giant snowman. The first detailed images beamed back from the US National Aeronautics and Space Agency’s (Nasa) New Horizons mission allowed scientists to confidently determine the body was formed when two spheres, or “lobes”, slowly gravitated towards each other until they stuck together — a major scientific discovery.

The New Horizons spacecraft 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, on Tuesday. 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 27,000 kilometres 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 briefing. “What this spacecraft and this team accomplished is unprecedented.” 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 kilometres 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.

“This is the first object that we can clearly tell was born this way,” Stern said, instead of evolving as a sort of “bi-lobe”. “This really puts the nail on the coffin now. We know that this is how these kinds of objects in many cases form.”

Some 4.5 billion years ago a cloud of frozen pebbles began to join forces, gradually forming two bodies — Ultima and Thule. Slowing turning, they eventually touched each other at what mission geology manager Jeff Moore called an “extremely slow speed” — maybe just one to a few kilometres per hour.

Published in Dawn, January 4th, 2019