Ultima Thule is shaped like two lumpy pancakes

New images reveal the skinny side of the Kuiper Belt object

ultima thule

THIN CRESCENT  This series of images, taken as the New Horizons spacecraft sped away from Ultima Thule, helped scientists determine that its shape is more like two pancakes than a snowman.


Visions of a space snowman have fallen flat.

New images of Ultima Thule released February 8 indicate that the faraway space rock is much thinner than thought. Rather than two round spheres stuck together like a snowman (SN: 2/2/19, p. 7), the object, officially called MU69, is shaped more like a couple of lumpy pancakes that melded together in a frying pan.

NASA’s New Horizons spacecraft flew by the Kuiper Belt object on New Year’s Day 2019 (SN Online: 12/30/18), and the spacecraft continued snapping shots past its point of closest approach. The new images were taken from a vantage point almost 9,000 kilometers beyond Ultima Thule, as New Horizons rapidly sped away.

By observing how Ultima Thule blocked out the light of background stars in a sequence of images, scientists mapped the shape of the hidden bits of the space rock that weren’t lit up by the sun’s rays. That information, combined with pictures taken from different angles earlier in New Horizons’ flight, allowed the researchers to visualize the space rock’s girth.

Scientists hope that studying Ultima Thule’s shape could help them understand how planets formed. The distant solar system denizen is thought to be one of the oldest objects in the solar system, so understanding its odd shape could help scientists come up with new theories for what the building blocks of planets are like.

THAT’S FLAT This animation reveals what scientists think Ultima Thule, whose official name is MU69, looks like from the side. While it looks like a roly-poly snowman face on, from the side, it is skinny.

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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