EXPERT REACTION: Super-rare space dirt found in Ryugu asteroid samples dropped in South Aussie outback

Hayabusa2 has provided us with a sample of asteroid Ryugu and it turns out to be a rare type of meteorite that only very infrequently arrives down on Earth. 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. But the representative CI meteorites are exceedingly rare, only 10 or so known, and they are vulnerable to terrestrial contamination and alteration from reaction with our oxygen and water-rich atmosphere. So the Ryugu sample gives us a chance to look at what these meteorites represent, free of any potential Earth involvement. Ryugu will now become a keystone sample in assessing many chemical signatures of the early solar system.

I did read through the paper and my first reaction was “holy sh**!” This is truly amazing. We’ve had other samples come back from other planetary bodies before, but never the most primitive material in the solar system. And we know how to access more of it if we want to. It actually has really blown my mind and I’ve been having a hard time putting it into words. I was considering using the word Rosetta Stone – but that’s probably a bit strong. On earth we have 70,000 meteorites (that we know of)  - of these only 9 are classified as CI. 5 of those were seen to fall. The total amount of material of these rocks is around 15 kg. We base almost all our comparisons of geologic processes on Earth to the compositions of these meteorites. I’m basically stuck in awe of this study at the moment and finding it hard to translate into normal words how interesting and important it is to have the source of this type of meteorite available for future study. 

Not only that, but 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 Hayabusa 2 mission to Ryugu is the most successful asteroid sample return ever. This new research shows that Ryugu is very similar to the Ivuna meteorite, which fell to Earth in Tanzania in 1938. 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’.
 
Out of over 50,000 known meteorites on Earth, there’s less than a dozen like Ivuna and Ryugu. They’re rich in water, and impacts from asteroids and meteorites like them may have been responsible for delivering water to Earth and the Moon early in the solar system’s history.
 
The Earth examples, though, are fragile. They’ve been contaminated by weathering, and have absorbed moisture and other chemicals. The Ryugu sample is pure, so it can tell us so much more.
 
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.

This work is absolutely fascinating, and really shows just how valuable samples from other objects in the Solar system are. By being able to bring home samples of Ryugu, and analyse them in the lab, astronomers can learn far far more than simply by studying the asteroid from a distance - or even sending a spacecraft there!

In this case, though, the samples reveal a really fascinating history for the material on Ryugu's surface. 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! 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. Since that period of 'aqueous alteration' (basically being chemically altered by water), the material has stayed in relatively cold storage - with temperatures likely never exceeding the boiling point of water, or a bit warmer!

If we'd only got hold of these samples as a result of a meteorite landing on Earth (the usual method of finding extraterrestrial material), it's likely we'd never have been able to learn as much, as the samples would have been polluted and altered by their time on Earth - so it is only because we were able to get the samples from Ryugu that the researchers were able to learn so much about what the samples had experienced, back when the Solar system was so young.

Indeed, it seems like the samples brought back from Ryugu are the most pristine sample of material from the Solar system's youth that we've ever encountered - and I'm sure that future studies will teach us a lot more about the Solar system's youth as a result.

CI chondrite meteorites are very rare. There’s only half a dozen in existence. They look like very fragile bits of coal. The wacky thing is, within error, they have the same composition as the sun. The sun isn’t just hydrogen and helium. There’s loads of other elements in there. Take the hydrogen and helium out of the sun and what you have is a CI chondrite. 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. It's just bonkers that – until now – we’ve only had these small numbers of meteorites to work with. But those few rocks define a calibration point for every other geochemical analysis. Every rock analysis is ratioed to CI chondrite and to average solar system.

These measurements from the Hayabusa-2 probe and its visit to Ryugu are amazing, quite literally out-of-this-world. Since the probe descended to the surface of the asteroid Ryugu, 'what was it going to show' and 'what was the asteroid like' were some of the big questions. The hope was that the samples would be some of the most pristine - bits that formed right after our Solar System formed, and that is exactly what has been shown. These samples from this asteroid are the leftover bits of the Solar System, the crumbs on the counter that you spill when making a cake.  It gives us insight into what the Solar System was like billions of years ago. 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. 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.

With this study, this is the first time ever that fragments from a pristine carbonaceous asteroid are analysed. 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. Results show that lots of liquid water circulated within Ryugu during the first 7 million years of its existence, when it was still hot. In an interesting twist, it also suggests that all the meteorites from C-type asteroids that fell on Earth had their composition modified upon or after landing, and no longer represent pristine material. Hence, Ryugu’s particles are currently the only one we have that are totally pristine!