A new study led by Dr. Alan Stern, planetary scientist and deputy director of the Southwest Research Institute (SwRI), believes that the large mounds about 5 kilometers long that dominate the appearance of the larger blade of the primitive Kuiper Belt object Arrokoth are similar enough to indicate a common origin. SwRI's research shows that these "building blocks" can provide guidance for further research into planet formation models.

This "building block" of Kuiper Belt objects may point to key details in flow instability models of planet formation.

Stern presented the findings this week at the 55th annual meeting of the American Astronomical Society's Division of Planetary Science (DPS) in San Antonio. The results were published Sept. 26 in the peer-reviewed Journal of Planetary Science.

In 2019, NASA's New Horizons spacecraft made a close flyby of Arokos. Based on these data, Stern and his collaborators found 12 mounds on Arokos' larger blade, Venu, that were nearly identical in shape, size, color and reflectivity. They also tentatively identified three additional mounds on the object's smaller blade, "Weeyo."

Dr. Will Grundy of Lowell Observatory, a co-investigator on the New Horizons mission, said: "It is amazing to see how well-preserved this object is, with its shape directly revealing the details that it is assembled from a set of building blocks that are very similar to each other. Arrokoth looks like a raspberry, made up of a number of small sub-units."

Observations of the Kuiper Belt object Arrokoth suggest that it was assembled from similarly sized objects that came together at low speeds in a localized region where gravitational collapse occurred. The findings support a flow-instability model of planet formation and are described in a new study led by Alan Stern, Ph.D., planetary scientist and associate director of the Southwest Research Institute (SwRI). Image source: NewHorizons/NASA/JHUAPL/SwRI/JamesTuttleKeane

Arrokoth's geology supports a flow-instability model of planet formation, in which collision speeds are only a few miles per hour and objects slowly accumulate in localized regions of the solar nebula that undergo gravitational collapse to form Arrokoth.

"The similarities in size and other properties of Arrokoth's mound structures suggest new insights into its formation," said Stern, principal investigator of the New Horizons mission. "If these mounds indeed represent the building blocks of ancient Earth-like planets like Arrokoth, then models of Earth-like planet formation will need to account for the preferred sizes of these building blocks."

It is possible that some of the flyby targets of NASA's Lucy Jupiter Trojan asteroid mission and ESA's Comet Interceptor are other primitive Earth-like planets, which may help understand the accretion processes of Earth-like planets elsewhere in the ancient solar system and whether they are different from those discovered by New Horizons in the Kuiper Belt.

"It will be important to look for mound-like structures on the Earth-like planets observed by these missions and see how common this phenomenon is to provide further guidance on theories of the formation of Earth-like planets," Stern said.