A photograph showing what Arrokoth looks like. Credit: NASA/Johns Hopkins APL/SwRI.

Scientists Explain Large Structures on Kuiper Belt Object Arrokoth

The odd structures could hint at a common origin, shedding light on the mysteries of planetesimal formation.


Arrokoth, a pristine Kuiper Belt object, is stirring up the space community with its unique mound structures. New findings led by Dr. Alan Stern of the Southwest Research Institute (SwRI) reveal that these mounds could hint at a common origin, shedding light on the mysteries of planetesimal formation.

Arrokoth’s Mound Structures: A Glimpse into the Past

According to the SwRI study, the mounds found on Arrokoth’s larger lobe, Wenu, measure approximately 5 kilometers in length and have striking similarities in shape, size, color, and reflectivity. This discovery was made possible by NASA’s New Horizons spacecraft, which closely observed Arrokoth in 2019. Stern and his team identified 12 such mounds on Wenu, and potentially another three on its smaller lobe, Weeyo.

Lowell Observatory’s Dr. Will Grundy, a key investigator of the New Horizons mission, expressed his astonishment: “It’s amazing to see this object so well preserved that its shape directly reveals these details of its assembly from a set of building blocks all very similar to one another.” He further added, “Arrokoth almost looks like a raspberry, made of little sub-units.”


The Streaming Instability Model

The unique geological features of Arrokoth validate the streaming instability model. This theory posits that planetesimals form when objects collide at gentle speeds, leading to their accumulation in specific areas of the solar nebula experiencing gravitational collapse.

Dr. Stern, the driving force behind the New Horizons mission, highlighted the significance of these findings. “Similarities including in sizes and other properties of Arrokoth’s mound structures suggest new insights into its formation,” he stated. Stern emphasized the need for planetesimal formation models to consider these building blocks’ preferred sizes.

The Road Ahead: More Discoveries Await

Upcoming missions, like NASA’s Lucy mission to Jupiter’s Trojan asteroids and ESA’s comet interceptor, are likely to encounter other untouched planetesimals. These observations could enhance our understanding of planetesimal accumulation processes in the ancient solar system and how they might differ from those found in the Kuiper Belt.


Stern concluded with a forward-looking statement: “It will be important to search for mound-like structures on the planetesimals these missions observe to see how common this phenomenon is, as a further guide to planetesimal formation theories.”

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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