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NASA's faraway space snowman has flat, not round, behind

11 February 2019

The final photos that NASA's New Horizons spacecraft snapped of Ultima Thule during the probe's epic January 1 flyby reveal the distant object to be far flatter than scientists had thought, mission team members announced today (Feb. 8). Ultima Thule is approximately 4.1 billion miles from Earth and about 1 billion miles past Pluto, making it the most distant celestial object ever explored. There have been different assumptions about its appearance: the most recent, based on images taken within a day of the beginning of the new year, was that both parts - Ultima, the large lobe, and Thule, the smaller one, were almost flawless spheres, barely touching each other, which NASA described as being just like a giant space snowman.

NASA's NewHorizons flew past Ultima Thule, an object located in a region of primordial objects 1 billion miles past Pluto.

"While the very nature of a fast flyby in some ways limits how well we can determine the true shape of Ultima Thule, the new results clearly show [the object] is much flatter than originally believed and much flatter than expected", said New Horizons project scientists Hal Weaver.

One lobe looks kind of like an oddly shaped "walnut", the agency said, while the other side looks like more a "pancake".

"But importantly, the new images are creating scientific puzzles about how such an object could even be formed. We've never seen something like this orbiting the Sun", he said. Add the fact that the spacecraft used long exposure times to boost the camera's signal level, and you've got some heavy blurring going on.

"Enlarge / The "old" view of Ultima Thule is on top". The images were taken almost 10 minutes after New Horizons crossed its closest approach point.

The new views were captured from a different angle than the snowman-suggesting photos, and they show Ultima Thule's outline against a number of background stars. Ultima Thule is actually composed of two joined shapes, named "Ultima" and "Thule", that were first thought to be both spherical, earning the nickname "snowman".

In order to deduce the object's shape, scientists watched the background stars on the images.

The "departure" movie comprising 14 shots taken by New Horizons during its flyby of Ultima Thule.

Alan Stern, New Horizons principal investigator, said: "This is really is an incredible image sequence, taken by a spacecraft exploring a small world four billion miles away from Earth". The flyby gave scientists the opportunity to collect photos and information about the rock that they hope will help solve some longstanding mysteries about the solar system's 4.5 billion years of history.

'Nothing quite like this has ever been captured in imagery'.

The discovery of MU69's considerably more svelte dimensions has scientists scratching their heads on how the shape of the thing fits in with current thinking on planetary formation.

As New Horizons beams more images through the solar system, we'll nearly certainly continue seeing weird, unprecedented stuff.

NASA's faraway space snowman has flat, not round, behind