Rubble recovered from an asteroid in near-Earth solar orbit may be the most “pristine” sample of cosmic rock on which we have yet had our primate legs.
According to a new and in-depth analysis of the material transported to Earth by the asteroid Ryugu, the rock and dust samples are among the most pristine Solar System materials we have ever had the opportunity to study, and their composition suggests that incorporating chemistry from the external parts of the system.
This not only offers us a unique tool to understand the Solar System and its formation, but it offers us a new context in which to interpret other space rocks that have been contaminated by contact with Land.
“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 pristine, unfractionated extraterrestrial materials studied to date and provide the best match available for the mass composition of the Solar System. “
About 4.6 billion years have passed since the formation of the Sun and the Solar System that surrounds it. Obviously it is a very long time and many things have changed since then; but we have time capsules that allow us to study the chemistry of the first solar system to understand how it all came together. These are fragments of rock, such as comets and asteroids, which have moved in space more or less unchanged since they formed.
Visiting a rock far from Earth is not easy, and collecting and returning samples even less. Historically, we have relied on the space rocks that came to us to put gloves on these time capsules. Meteorites known as carbonaceous chondrites were the best tool available for probing the composition of asteroids that may have supplied Earth with water, as the Solar System was still forming.
However, this record is influenced by a kind of mineral version of survival of the fittest. Only the strongest chunks of space rock persist through the explosive rigors of entering the atmosphere, and even then they are altered and contaminated by the Earth’s environment.
In recent years, venturing to land on asteroids has been within our capabilities. In December 2020, a probe sent to Ryugu by the Japanese Space Agency (JAXA) unloaded a priceless payload: material samples collected from the asteroid’s surface and transported home in sterile containers.
Scientists have since eagerly studied the contents, revealing that the asteroid is very similar in composition to those carbonaceous chondrites, making it what we call a C-type asteroid. It also contains prebiotic molecules – the precursors of biological compounds – and may have been once a comet.
The new analysis delves further. Ito and his colleagues found that the abundances of heavy hydrogen and nitrogen in the asteroid are consistent with an origin in the outer solar system; that is, Ryugu began his life much farther from the Sun. This would be consistent with the comet theory, since those frozen bodies are visitors from the farthest reaches of the Solar System.
Ryugu, the researchers found, also has a noticeable difference from carbonaceous chondrites. The asteroid samples lack ferrhydrite (compounds of iron and oxygen) and sulfate (sulfur and oxygen). Since these compounds are found in meteorites, they were thought to be components of extraterrestrial materials. Their lack in Ryugu suggests that they could be the result of terrestrial weathering in meteorites.
This means that future meteor studies should take this possibility into account … and that future asteroid sample return missions will be able to shed more light on the matter.
“In this study we prove it [carbonaceous] Meteorites, despite their geochemical importance as a proxy for the mass composition of the Solar System, are earth-level contaminated samples, “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 the returned samples in totally inert and sterile conditions. The evidence presented here shows that Ryugu particles are undoubtedly among the materials of the System. The most pristine solar available for the laboratory the study and ongoing investigations of these precious samples will certainly broaden our understanding of the early solar system processes. “
The research was published in Astronomy of nature.