‘Space snowman’ Arrokoth reveals how planets are formed
Arrokoth -- the ultra-red, peanut-shaped object is located 4.1 billion miles (6.6 billion km) from Earth.
A NASA probe's epic encounter with a vaguely hourglass-shaped icy object called Arrokoth in the far reaches of the Solar System is telling us a lot about the formation of the planets, including Earth.
Arrokoth -- the ultra-red, peanut-shaped object -- is located one billion miles beyond Pluto in the Kuiper belt, a vast donut-shaped region that is home to thousands of dwarf planets and icy objects.
This object has two distinct lobes, both of which are surprisingly flattened, scientists say. Arrokoth thus looks like a space snowman, but the one that's been beaten and bloodied.
On Thursday, scientists offered the fullest description yet of the composition and origin of Arrokoth based on data from NASA's New Horizons spacecraft, which whizzed past it in 2019.
Arrokoth -- 4.1 billion miles (6.6 billion km) from Earth –has a surface that is smooth and undulating with few craters. It is coated with frozen methanol - a type of alcohol - and unidentified complex organic molecules.
About 22 miles (36 km) long and 12 miles (20 km) wide, it is classified as a planetesimal -- objects that were among the Solar System's original building blocks. These small bodies coalesced at an early stage of the Solar System's formation some 4.5 billion years ago and are a key intermediate size step on the way to building planets.
Arrokoth’s two lobes look like giant wheels of cheese fused together by a bridge.
"It consists of two bodies that appear to have formed in orbit around each other from a local dust cloud, which collapsed under its own gravity within the solar nebula - the huge disk of dust and gas that the solar system formed from,” said astronomer John Spencer of the Southwest Research Institute in Colorado, one of the researchers in the study published in the journal Science.
The two bodies then spiralled in together and merged very gently," he added.
This suggests that planetesimals formed in localized conditions in which collision speeds were slow rather than from a gradual assembly of widely dispersed objects growing by randomly colliding with each other at higher speeds.
"So we now have a clearer picture of how planets, including the Earth, were built," Spencer said.
"Planetesimals previously visited by space probes were all badly battered by impactors or cooked by approaching too close to the Sun. So it is thrilling to finally be able to see one still pretty much just as it was after its formation," said planetary scientist and study co-author Will Grundy of Lowell Observatory in Arizona, a New Horizons mission co-investigator.
Arrokoth is one of the thousands of small icy bodies inhabiting the Kuiper Belt, the Solar System's vast "third zone" beyond the inner terrestrial planets and the outer gas giant planets. Its name is a Native American term for "sky."