These asteroid particles may be our most ‘primitive’ samples of the outer solar system

Crushed rock recovered from asteroids in near-Earth solar orbit may be the most “primitive” cosmic rock samples on our primate claws.

Rock and dust samples are among the most uncontaminated solar system materials we’ve had a chance to study — and their composition suggests they bind the system’s periphery, according to a new in-depth analysis of material transported to Earth from asteroid Ryugu chemical substances.

Not only does this give us a unique tool to understand the solar system and its formation, it also gives us new context to explain other space rocks that have been contaminated by contact with the solar system Earth.

“Ryugu particles,” wrote a team led by cosmochemist Motoo Ito of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), “are the most uncontaminated and unclassified extraterrestrial material ever studied, and provide the Bulk Solar System Composition.”

About 4.6 billion years have passed since the formation of the sun and the surrounding solar system. Obviously that was a long time and a lot has changed since then; but we do have time capsules that allow us to study the chemistry of the early solar system to see how it all fits together. These are large rocks, like comets and asteroids, that have been drifting through space more or less unchanged since their formation.

Accessing rocks far from Earth is not easy, nor is collecting and returning samples. Historically, we’ve relied on space rocks for these time capsule gloves. When the solar system was still forming, meteorites known as carbonaceous chondrites were the best tools for probing the composition of asteroids that might have delivered water to Earth.

However, this record has been misled by a mineral version of the survival of the fittest. Only the strongest chunks of space rocks can survive the explosively harsh conditions that enter the atmosphere, and even then they are altered and polluted by the terrestrial environment.

In recent years, risky landings on asteroids have been within our reach. In December 2020, a probe sent to Ryugu by the Japan Space Agency (JAXA) unleashed a valuable payload: a sample of material collected from the asteroid’s surface and transported home in sterile containers.

Since then, scientists have been eagerly studying its contents, finding that the asteroid is very similar in composition to those carbonaceous chondrites, hence the name C-type asteroid. It also contains prebiotic molecules — precursors to biological compounds — and may have been a comet.

The new analysis goes deeper. Ito and his colleagues found that the abundance of heavy hydrogen and dinitrogen in the asteroid is consistent with the origin of the outer solar system. That is, Ryugu’s life begins farther from the sun. This is consistent with comet theory because these icy objects are visitors from farther out in the solar system.

The researchers found that Ryugu also has a distinct difference from carbonaceous chondrites. Ferrihydrite (a compound of iron and oxygen) and sulfate (sulfur and oxygen) were missing from the asteroid samples. Because these compounds are present in meteorites, they are thought to be part of extraterrestrial material. The lack of them in Ryugu suggests that they may be the result of terrestrial weathering in meteorites.

This means that future meteorite research should take this possibility into account…and future asteroid sample-return missions will be able to shed more light on this question.

“In this study, we demonstrated [carbonaceous] Meteorites, despite their geochemical importance as representatives of the overall composition of the solar system, are samples of terrestrial contamination,” the researchers wrote in their paper.

“The results of this study clearly demonstrate the importance of direct sampling of primitive asteroids and the need to transport returning samples under completely inert and sterile conditions. The evidence presented here shows that Ryugu particles are unquestionably laboratory-ready The study and continued investigation of these precious samples, one of the most uncontaminated solar system materials, will certainly expand our understanding of early solar system processes.”

The research has been published in natural astronomy.

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