Arrokoth And The Many Mysteries Of The Primordial Sky

In the very reaches of our Solar System, there is a remote, dim realm of perpetual dusk, where our Sun will softly shine with just a small, weak spark. It is the birthplace of the dwarf planet Pluto, its large frigid satellite, Charon, and a multitude of other frozen bodies that involve a dancing sea of icy comet nuclei, which is called the Kuiper belt. Fragile and ephemeral, comets that strike inward towards our Star’s brilliant light and melting heat, are the fleeing refugees from this remote perpetual dusk region.

Planetary scientists from NASA’s New Horizons mission to Pluto and beyond announced in February 2020 that data collected from this mission provide new insights into how planets and planetesimals — the building blocks of planets — were born in our primary solar system. On January 1, 2019, the New Horizons spacecraft soared past the ancient Kuiper belt object (KBO) Arrokoth (2014 MU 69), providing humanity with its very first close-up view of one of those mysterious icy relics of the birth of our Solar System nearly five billion years ago.

Using detailed data on the shape, geology, color, and composition of Arrokoth — collected during a record-setting flyby that took place over 4,000,000,000 miles from the Earth — planetary scientists announced in February 2020 that they were able to answer a long-standing question about planetesimal origins and have therefore made significant progress in our understanding of how the planets themselves live. These findings are reported by the team in a set of three papers published in the Science journal issue of February 13, 2020. The scientists also presented their findings at a media briefing held at the Seattle, Washington, annual meeting of the American Association for the Advancement of Science (AAAS).

486958 Arrokoth is the tentative name of the trans-Neptunian entity MU 69 from 2014. It is a binary contact, 22 miles long, consisting of a duo of icy primordial planetesimals which is 13 miles and 9 miles across. The two planetesimals have respectively been called Ultima and Thule, and are joined together along their main axes. Ultima is flatter than Thule, and in reality, it is an aggregation of 8–or more — smaller items, each around 3 miles long. It is thought that these smaller objects fused together before Ultima and Thule met up and merged together. Although there have been evidently no-or rather few-catastrophic impacts on Arrokoth since it was formed, the past of its creation has been stored in the deep freeze of our Solar System, far from the molten sun of our roiling Star.

Arrokoth is both the most distant and primitive object that a spacecraft can visit in our Solar System. Dr. Marc Bule and the New Horizons Search Team discovered it on 26 June 2014 using the Hubble Space Telescope (HST) as part of a hunt for the KBO that would become New Horizons’ target in its first extended mission. This discovery required the use of the HST because Arrokoth is far too weak to be observed with an apparent magnitude of only 26 — except for the most powerful telescopes. The HST is also capable of conducting extremely accurate astrometry. That means it can deliver a reliable orbit determination.

Arrokoth was chosen over two other KBO candidates, and thus became the target for the extended quest beyond Pluto to New Horizons. Arrokoth is designated as a cold classical KBO with an orbital period of approximately 298 years and low orbital tendency and excentricity.

The provisional name Arrokoth itself originates from the Powhatan area of Virginia and Maryland, where the discovery of Arrokoth took place. The HST and Johns Hopkins Applied Physics Laboratory are both based in Maryland and are largely responsible for the detection of Arrokoth in 2014.

Pluto And Beyond

On July 14, 2015, New Horizons hit its primary goal in the Kuiper belt—the ice dwarf planet Pluto and its band of five icy moons—including its main moon, Charon, which is roughly half the size of Pluto, after its hazardous decade-long odyssey through space. New Horizons, having recently achieved its groundbreaking closest approach to the Pluto planet, sent some surprising photos of this far-away tiny universe with a huge heart back to Earth.

Astronomers found Pluto to be a desolate little planet for much of the 20th century, where it dwells in the outer reaches of our solar system. However, that point of view changed back in 1992, when a second KBO in this region was discovered. Because of this observation, planetary scientists began to know that in this distant frozen area of eternal dusk, Pluto is far from alone. Pluto, in reality, circles our Star in the company of countless others of his enigmatic frigid existence. Since 1992, astronomers searching for those distant bodies have discovered a multitude of other icy, rocky little worlds, very similar to Pluto.

Some of the other distant denizens of the deep freezing of our solar system also orbit our Star in eccentric orbits — as Pluto does. The dwarf planet Eris is one of the most significant of these dispersed disc objects. Eris, found back in 2005, is a bit more huge than Pluto and his finding is what pushed planetary scientists to understand that Pluto is only one of the millions. As a result, poor little Pluto was unceremoniously evicted from the pantheon of main planets at the period, and is now known as an ice cube — a pure dwarf planet, but still a planet. Prior to this, Pluto had been classified as our Star ‘s ninth major planet.

It is generally thought that KBOs consists mainly of a combination of ice and rock. The Kuiper belt extends from Neptune’s orbit to about 50 Astronomical Units ( AU). One AU is equivalent to the mean distance of about 93,000,000 miles between Earth and Sun. The average distance between Neptune and our Star is around 30.1 AU — its perihelion (when it is nearest to our Star) is 29.8 AU, while its aphelion (when it is farthest from our Star) is 30.4 AU.

The New Horizon spacecraft was maneuvered for its future flight over the distant Arrokoth, after completing its primary mission of a flyby over Pluto and its moons.

Arrokoth And Its Many Mysteries

Arrokoth has a unique story to tell us, as the most remote, primitive, and the purest object ever explored by a spacecraft. This remote little object has enabled planetary scientists to make significant progress in understanding how planets formed within the primordial Solar System. The first post-flyby photos collected in 2019 from New Horizons showed that Arrokoth currently consists of two intertwined blades with smooth surfaces, as well as the same composition. This means that it is most certainly a pure specimen and as such offers useful details about how it was made.

These interesting new findings contribute to a large number of historical achievements of an important mission. NASA ‘s discoveries from New Horizons have enhanced our understanding and knowledge of how planetary bodies were born in our Solar System — as well as in distant planetary systems beyond our own.

The New Horizons team plans to use the data more resolutely in the future. Also, the scientists plan to use sophisticated supercomputer simulations to create models of how Arrokoth might have formed trillions of years ago.

Their analysis has already revealed that the “binary contact” lobes of Arrokoth were originally two separate objects, orbiting at slow velocities close to each other. Ultimately, the duo collided gently and merged to form the 22 mm body New Horizons observed.

This evidence suggests that Arrokoth was formed in the initial primordial solar nebula, which gives rise to our Universe and its family of planets, stars, and other objects, around 4.56 billion years ago after the gravitational collapse of solid particle cloud. The particles that formed Arrokoth collided peacefully as the cloud exploded, in sharp comparison to a high-speed crash and systemic aggregation. This indicates that Arrokoth, and other similar objects that inhabit the ancient Solar System, gradually grew in size to form ever larger and larger bodies. In a way comparable to how fossils show how species evolved on our own planet, lingering planetesimals like Arrokoth reveal how planets evolved in our own Solar System — and beyond.

If Arrokoth had evolved as a consequence of a violent crash in our primordial solar system, it might not look the way it does. Instead, evidence suggests that it was formed as a result of a more complex and gentle ballet in which the two dancing planetesimals slowly orbited each other before their dance gravitationally drew them both together, thus forming the two-lobed single planetesimals observed today.

This scenario is supported by two further important lines of evidence. Arrokoth ‘s uniform surface structure and color show that it was created from materials dancing similarly to each other, as expected by local patterns collapsing within clouds. This compares with a hypothesis suggesting that it was created from material found in regions of the primordial solar nebula which are more broadly spaced.

Additionally, the flattened form of each of the two lobes of Arrokoth, as well as its very narrow polar alignment and equator, indicates that it was born in an orderly cradle. Also, the smooth surface of Arrokoth suggests that its face has been well preserved since the end of the era of planet formation in the dusky deep freezing of our Solar System. This means that Arrokoth displays physical properties that indicate that it was formed in the solar nebula as a result of gradually and gently merging objects that formed close to one another.

The three papers published in the journal Science’s February 13, 2020 issue are based on ten times as much data as the first reports published about the new findings. The papers together give a more complete portrait of the mysterious origins of Arrokoth.

New Horizons is continuing to observe dancing objects in the distant Kuiper belt. The New Horizons team is planning to use a large telescope on Earth in the summer of 2020 to hunt for additional KBOs that can be studied — and also look for other potential targets for the spacecraft.

The New Horizons spacecraft is about 7.1 billion kilometers from Earth as of this writing. It is still running normally, as it rises at speeds of nearly 50,400 kilometers per hour across this unexplored, frigid twilight zone.

New Horizons Principal Investigator Dr. Alan Stern explained their reasons for giving Arrokoth its name:

“The name ‘Arrokoth’ reflects the inspiration to look to the skies and wonder about the stars and worlds beyond our own. That desire to learn is at the heart of the New Horizons mission and we are honored to join the Powhatan community and the Maryland people in this discovery celebration.”

arrokoth and the many mysteries of the primordial sky