Evrim Yazgin
Cosmos science journalist
When space dust from the near-Earth asteroid 162173 Ryugu landed in the red desert sands of South Australia a year-and-a-half ago, it was the culmination of a six-year, 5.24-billion-kilometre journey. Now, the analysis of the most treasured 5.4 grams of dirt on Earth (from space) has revealed the rare and untouched clues to the building blocks of the early solar system.
Japan Aerospace Exploration Agency spacecraft Hayabusa2’s samples from Ryugu touched down in the Australian outback in December 2020. Ryugu is a carbonaceous chondrite (also CI chondrite or C1 chondrite), meaning it is made from carbon-rich rock.
Scientists have previously only had the opportunity to study the make-up of asteroids when a small handful of meteorites have crash landed on Earth. But, by this point, the material is “contaminated” by Earth’s own matter.
Ryugu has provided researchers the opportunity to look at a pristine sample from the creation of our solar system 4.6 billion years ago, offering a window into the geological and chemical make-up of the solar system – including our own planet – as it was forming.
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Results of the international effort to analyse the tiny amount of material returned from Ryugu have been published in Science.
Ryugu is a very rare type of meteorite, with only around 10 known to science, says Trevor Ireland, earth sciences professor at Australian National University (ANU). “CI chondrites may be rare, but they may be the closest representative of the molecular dust cloud that collapsed to form our solar system 4,567 million years ago. They also contain abundant organic molecules and water – two of the essential ingredients in the building of proteins to make life.”
“These samples were formed 37 million years after the first solid stuff in our solar system – a precise measurement of how long they’ve been around for,” explains Brad Tucker, a research fellow at ANU. “It also tells us that meteorites from similar type asteroids are a bit contaminated as they pass through the Earth’s atmosphere, shedding light on how we can use meteorites that fall to Earth to better understand the solar system.”
“Take the hydrogen and helium out of the sun and what you have is a CI chondrite,” says Phil Bland, director of the Space Science and Technology Centre at Curtin University. “Because most of the mass of the solar system is in the sun, if you want to pick a composition for average solar system stuff, it’s CI chondrite. It’s what everything was made from.”
“We’ve had other samples come back from other planetary bodies before, but never the most primitive material in the solar system,” says Gretchen Benedix, an astrogeologist at Curtin University. “And we know how to access more of it if we want to.”
Benedix also believes that study of Ryugu’s composition can help sharpen current techniques for identifying asteroids in the solar system. “This also helps with creating a geologic map of the solar system. We currently classify asteroids based on how their surfaces reflect sunlight. Doing laboratory experiments that simulate this showed that asteroids are the most likely source of many of the meteorites we have. Having this direct link to the most primitive material will let us better unravel those reflected sunlight signals (spectra).”
“Japan’s Hayabusa2 mission to Ryugu is the most successful asteroid sample return ever,” adds Flinders University associate professor Alice Gorman, an internationally recognised leader in the emerging field of space archaeology.
“Bizarrely, the composition of Ryugu is very like the outer layer of the Sun. This indicates that its parent body was formed at around the same time at the beginnings of the solar system, about 4.6 billion years ago. It’s a fascinating window into a time when the planets were coming into being and the Sun was still young.”
“Back when the solar system was young, the material that now makes up Ryugu was part of a larger ‘parent planetesimal’, which has long since been shattered and torn asunder,” says Jonti Horner, an an astrobiologist and astronomer from the University of Southern Queensland. “The results of the new analysis show that the minerals in the sample were exposed to relatively warm (around body temperature) liquid water when the parent object was young – just five million years after the solar system formed.”
Gorman and others hint that Ryugu and asteroids like it might hold the key to the origins of life on Earth and beyond.
“This new research shows that Ryugu is very similar to the Ivuna meteorite, which fell to Earth in Tanzania in 1938,” Gorman says. “Some researchers have claimed there are fossils of microbes inside Ivuna, but as with most of these claims, it’s more wishful thinking than reality. Ivuna-class meteorites do, however, contain abundant amino acids, which are often called the ‘building blocks of life’.”
“With this study, this is the first time ever that fragments from a pristine carbonaceous asteroid are analysed,” says Fred Jourdan, Curtin University professor and director of the Western Australian Argon Isotope Facility. “This is very significant because C-type asteroids such as Ryugu contain lots of carbon and water, the building block of organic matter, which, in fact, may well have provided material to start life on Earth. This study shows that these samples are the most pristine undisturbed samples that we have on Earth and they provide the clearest picture yet of the conditions reigning at the very beginning of the solar system.”
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