Humorously dubbed a “space peanut” by enthusiasts, the latest imagery confirms that Ultimate Thule is an example of contact binary, an astronomical event where two celestial objects fuse. It is the first contact binary explored by spacecraft, Stern told reporters. Scientists on the mission estimate it formed 4.5 billion years ago and hope it can offer a glimpse into the building blocks of our solar system.

A comet is born

The rendering below show the process that made Ultimate Thule. Pebbles slowly swirled together, fusing to each other until only two large objects remained. Rotating around each other, “Ultima” and “Thule” grew tighter in orbit until they came together at a speed of one to two miles per hour. Speeds so slow that, “if you hit a car at the speed, you’d probably not fill out insurance forms,” joked Jeff Moore, New Horizons Geology and Geophysics team lead.

More than 4 billion years later, the axis of rotation remains. Cathy Olkin, New Horizons’ deputy project scientist, says “we now know that Ultima rotates within a period of 15 hours, give or take one hour.”

Artists representation of the formation of Ultima Thule.
A cloud of icy bodies ultimately form two large objects that became Ultima Thule.
Image: NASA / JHUAPL / SwRI / James Tuttle Keane

A red peanut

NASA scientists created a color image of Ultima Thule using sensors that detect visible and near-infrared light. ”Color variations tell us how the Ultima Thule was formed,” says Howett. It’s likely that the surface of the comet’s been charred over the years from cosmic radiation, an “irradiation of exotic ices.”

The surface’s brightness can provide clues to scientists about its composition. The neck, for instance, is perhaps brighter because it’s a finer material. It could even be an entirely different substance than the rest of the object, says Moore.

With less than 1% of the data NASA will eventually receive, more discoveries await us. NASA’s will share its next findings (and potentially an even higher-resolution image) on Jan. 3 at 2:00PM (ET).

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