A trip to the most remote part of our solar system has given some surprising insights into the formation of our own planet. Three new studies based on data collected about NASA's flyby at Arrokoth – the most distant object in the solar system and the oldest body ever examined – give researchers a better idea of how the building blocks formed by planets and how Arrokoth's surface is and why it looks like a giant circus peanut.
Arrokoth is a 21 mile wide space object that was formed approximately 4 billion years ago. It is located behind Pluto in the Kuiper belt and is much less abused than other primitive bodies that sit in asteroid belts or closer to the sun. "[The objects] this form there has basically not been disturbed since the beginning of the solar system," said William McKinnon, lead author of one of the studies, at a press conference.
That is, Arrokoth does not do this despite his age. It doesn't look much different today than it did billions of years ago, making it the perfect tool for researching the origins of planets.
Before these new findings there were two competing theories about how the solid building blocks of planets or planetesimals are formed. The first theory is called hierarchical accretion and states that planetesimals occur when two separate parts of a nebula – the gas and space dust cloud born from a dying star – collide.
The Latest Observations of Arrokoth Support The Second Theory: Instead of a sudden, violent collision, planetesimals form when gases and particles gradually collect in a fog to the point where they become too dense for their own gravity withstand. Nearby components gradually merge and a planetesimal is born. "All of these particles fall toward the center, then they make a large planetetesimal. Maybe 10, 20, 30, 100 kilometers in diameter," said McKinnon, professor of earth and planetary science at Washington University. This type of cloud collapse typically results in binary shapes rather than smooth spheroids, hence Arrokoth's peanut-like silhouette.
If this is the origin of Arrokoth, it was probably the origin of other planetesimals, including those that made up the earth. "In this way, the planetesimal formation took place via the Kuiper belt and possibly via the solar system," said Alan Stern, chief researcher at New Horizons, at the briefing.
The study package, published in the journal Science also contains knowledge about the appearance and substance of Arrokoth. In their work, planetary scientist Will Grundy and his colleagues from Northern Arizona University reveal that the surface of the body is covered with "ultrarotated" matter that is so thermodynamically unstable that it cannot exist closer to the sun at higher temperatures.
The ultra red color is a sign of the presence of organic substances, namely methanol ice. Grundy and colleagues speculate that the frozen alcohol could be the product of water and methane ice, which react with cosmic rays. New Horizons has not discovered water in the body, but the researchers say that H2O may have been present but not visible. Other unidentified organic compounds were also found on Arrokoth.
The Pluto and Arrokoth flyby through New Horizon took place within a few days. To get a better understanding of how the object was formed and what it is made of, researchers need to find a way to send a probe to the Kuiper Belt for an extended period of time, possibly including it in the orbit of a larger body. Such a mission could tell us even more about the childhood of the solar system and the composition of the outer boundaries of our planetary neighborhood.