Debris recovered from an asteroid in near-Earth solar orbit may be the most “virgin” sample of space rock we’ve ever had primate paws on.
According to a new, in-depth analysis of material delivered to Earth by the asteroid Ryugu, the rock and dust samples are among the most uncontaminated Solar System materials we’ve ever had the chance to examine—and their composition suggests they incorporate chemistry from outsiders. parts of the system.
This not only gives us a unique tool for understanding the Solar System and its formation, but gives us a new context in which to interpret other space rocks that have been contaminated by contact with The Earth.
“The Ryugu particles,” wrote a team led by cosmochemist Motoo Ito of the Japan Agency for Marine Earth Science Technology (JAMSTEC) in Japan, “are the most uncontaminated and unfractionated extraterrestrial materials studied to date, and provide the best available match with bulk composition of the solar system.”
About 4.6 billion years have passed since the formation of the Sun and the Solar System around it. Obviously, that’s a very long time and a lot has changed since then; but we have time capsules that allow us to study the chemistry of the early solar system to understand how it all happened. These are chunks of rock, such as comets and asteroids, that drift through space more or less unchanged since they formed.
Visiting a rock far from Earth is not easy, and collecting and returning samples even less so. Historically, we’ve relied on space rocks coming our way to get our mitts on these time capsules. Meteorites, known as carbonaceous chondrites, are the best available tool for studying the composition of asteroids that may have delivered water to Earth as the solar system was still forming.
However, this record is biased by a kind of mineral version of survival of the fittest. Only the most robust pieces of space rock survive the explosive rigors of atmospheric entry, and even then they are altered and contaminated by the Earth’s environment.
In recent years, daring to touch asteroids has come within our reach. In December 2020, a probe sent to Ryugu by the Japan Space Agency (JAXA) dropped off a priceless payload: samples of material collected from the asteroid’s surface and transported home in sterile containers.
Since then, scientists have eagerly studied the contents, revealing that the asteroid is very similar in composition to these carbonaceous chondrites, making it what we call a C-type asteroid. It also contains prebiotic molecules—the precursors to biological compounds—and may once have been a comet. .
The new analysis goes even deeper. Ito and his colleagues found that the abundance of heavy hydrogen and nitrogen in the asteroid is consistent with its origin in the outer Solar System; this means that Ryugu started life much further away from the Sun. This would be consistent with the comet theory, as these icy bodies are visitors from the far reaches of the solar system.
Ryugu, the researchers found, also has one distinct difference from carbonaceous chondrites. The asteroid samples lack ferrihydrite (compounds of iron and oxygen) and sulfate (sulfur and oxygen). Because these compounds are found in meteorites, they are believed to be a component of extraterrestrial materials. Their absence in Ryugu suggests that they may be the result of terrestrial weathering in the meteorites.
This means that future studies of meteorites should take this possibility into account… and that future missions to return asteroid samples will be able to shed more light on the matter.
“In this study, we demonstrate that [carbonaceous] meteorites, despite their geochemical importance as proxies for the bulk composition of the Solar System, are terrestrially contaminated samples,” the researchers wrote in their paper.
“The findings of this study clearly demonstrate the importance of direct sampling of primitive asteroids and the need to transport the returned samples in completely inert and sterile conditions. The evidence presented here shows that the Ryugu particles are undoubtedly among the most uncontaminated material in the Solar System available to the laboratory, and ongoing research on these precious samples will certainly expand our understanding of early processes in the Solar System.”
The study was published in Natural astronomy.