NASA’s New Horizons mission is providing new insights into how planets and planetesimals, which are the building blocks of planets, were formed. When the New Horizons spacecraft flew past a Kuiper Belt object called Arrokoth last January, it gave us the first look ever at a remnant of the formation of the solar system. The team used data on Arrokoth’s shape, geology, color, and composition to answer questions about the origins of planetesimals and how the planets formed.
Arrokoth is teaching the team how planetesimals formed, and they believe it is giving them advances in the understanding of overall planetesimal and planet formation. The first images of Arrokoth showed that it had two connected lobes, a smooth surface, and uniform composition. Those details indicated the object was pristine.
In the following months, the team worked with more and higher-resolution data as well as computer simulations to assemble a picture of how Arrokoth must have formed. The analysis indicates that the lobes of the “contact binary” object were once separate bodies that formed close together at low velocity. The team says that they orbited each other and “gently” merged to create the 22-mile long object.
This indicates that Arrokoth formed during the gravity-driven collapse of a cloud of solid particles in the primordial solar nebula rather than by a competing theory of planetesimal formation called hierarchical accretion. The team says that the flattened shapes of the lobes and close alignment of their poles suggest an orderly merger from a collapsing cloud.
Scientists say that Arrokoth wouldn’t have formed or look the way it does if it had been created in a more chaotic accretion environment. The team says all the evidence found suggests a particle-cloud collapse model. New Horizons is still performing observations Kuiper Belt objects it passes on its travels.