Kuiper Belt Object Reveals Secrets of Planetary Building Blocks

(CN) – A trove of NASA spacecraft data from a visit to the farthest planet-like object in the solar system – a planetesimal in an icy region beyond the orbit of Neptune – reveals how planetary building blocks form over time, astronomers said in a trio of studies released Thursday.

After an historic 2019 mission at the edge of the solar system, NASA’s New Horizons spacecraft sent back a photo of Arrokoth, an object initially called Ultima Thule by researchers.

The uniform color and composition of Arrokoth’s surface shows the Kuiper Belt object formed from a small cloud of material in the solar nebula, rather than from various objects from dispersed regions of the nebula, researchers said. (NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Institute / Roman Tkachenko)

Arrokoth – meaning “sky” in the Powhatan/Algonquian language – lies within the Kuiper Belt, a distant, thick ring of icy bodies that also counts Pluto among its members.

The object is bilobal, meaning it’s made up of two fused spheres that once orbited the sun and later combined into a single object after the formation of the solar system.

After early reports described Arrokoth as the oldest and most primitive object ever observed in the solar system, researchers are building upon the mission’s initial findings, according to reports published Thursday in Science.

The new analysis details the composition and origin of Arrokoth and points to answers for how planetesimals form in the cosmos.

Washington University researcher William McKinnon and colleagues plugged NASA’s flyby data into a simulation that found two objects formed independently of each other and, after a very long period, gently melded into what is now Arrokoth.

The object formed within a collapse cloud of the solar nebula and not by another theory of planetesimal formation called hierarchical accretion, in which objects from various regions of the nebula collided to form Arrokoth, the study said.

A study by Southwest Research Institute’s John Spencer and colleagues found Arrokoth is less flat than previously believed and also contains more volume than prior estimates.

The object has a smooth, lightly cratered surface – characteristics that diverge from similar objects observed in the solar system – meaning it has been mostly preserved since the end of the planet formation era, the study found.

An analysis of crater density on the object, which takes 293 Earth years to orbit the sun, confirmed its age of more than 4 billion years.

Lowell Observatory scientist Will Grundy and colleagues set out to examine the composition, color and temperature of Arrokoth’s surface. The object’s face is uniformly red, frigid, and dotted with methanol ice along with complex organic molecules of unknown origin, they found.

Researchers believe methanol on Arrokoth’s surface could have been formed by cosmic ray irradiation of mixed water and methane ices, according to the study. The authors have not ruled out the presence of water on Arrokoth, saying in the study water in some form may be hidden from view or masked in some way.

The object’s uniform color also supports the finding that Arrokoth was formed in a local solar nebula collapse cloud, researchers said in the study.

Spencer told Courthouse News the process within the solar nebula that created Arrokoth would have occurred millions of times over its lifetime.

“We think the local collapse occurs when the motion of the gas in the solar nebula concentrates enough solid material in a small region that the solid material pulls itself together by its own gravity to form larger objects,” Spencer said. “This is very different from the earlier model of planet formation, in which objects on independent orbits around the sun collide randomly with each other at relatively high speeds, and gradually build up larger and larger objects.”

Dwarf planets and other bodies called trans-Neptunian objects also lie within the Kuiper Belt.

Arrokoth was first discovered by New Horizons mission member Marc Buie in 2014 using NASA’s Hubble Space Telescope. The New Horizons mission launched in 2006 and made the first flyby of Pluto nine years later.

High-resolution photos and other data related to Arrokoth made it back to NASA after a six-hour journey across 4 billion miles of space.

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