Hayabusa2's Ancient Asteroid Samples Are the Most Pristine Ever Seen. Why That's a Big Deal
Jackson RyanFormer Science Editor
Jackson Ryan was CNET's science editor, and a multiple award-winning one at that. Earlier, he'd been a scientist, but he realized he wasn't very happy sitting at a lab bench all day. Science writing, he realized, was the best job in the world -- it let him tell stories about space, the planet, climate change and the people working at the frontiers of human knowledge. He also owns a lot of ugly Christmas sweaters.
Now, some eighteen months later, the chest has been opened and its treasures subjected to the full gamut of scientific analyses. The Japanese space agency, JAXA, had an inkling that the precious materials inside Hayabusa2's sample capsule would be of great scientific value -- and the initial chemical analysis shows just how remarkable the agency's samples are.
In a study, published in the journal Science on June 9, JAXA scientists provide the first in-depth assessment of samples recovered from Ryugu since they were returned to Earth.
"We found Ryugu is the freshest ever CI chondrite," said Shogo Tachibana, JAXA's lead scientist on the initial sample analysis.
What this means is the materials recovered from Ryugu are the most primitive humans have ever been able to analyze on Earth. They provide a portal to the very early days of the solar system, when the sun was only a fledgling star and the planets were only just starting to form. Though the study released Thursday is a major milestone in understanding Ryugu, it's merely the first step in comprehending the solar system and our place in it.
Here's why it matters.
Journey to the Dragon Palace
Japan's Hayabusa2 mission launched in 2014 on a journey to retrieve samples from the asteroid Ryugu, named for the "Dragon Palace" in a famous Japanese folktale. The asteroid belongs to the most common class in our solar system, the C-type, and is shaped like a spinning top. Its orbit around the sun exists beyond Mars. Some scientists believe these types of asteroids delivered the raw materials for life to Earth, and that's why JAXA wanted to investigate Ryugu and steal some rock from its surface.
After a four-year journey, Hayabusa2 rendezvoused with the space rock and then, in 2019, the spacecraft made two brief touchdowns on the asteroid, hoovering up samples and storing them in a specialized sample capsule. That sample capsule landed in the Australian outback in 2020 and its precious cargo has been carefully managed since.
The two landings on Ryugu snatched away 5.4 grams of material from the surface and subsurface of the asteroid. The material is in the form of small pebbles and rocks, ranging in size up to about 0.4 inches. The study released on June 9 took an extremely tiny amount of the sample -- about 2% of the total -- to examine the chemistry and structure of the asteroid and draw some conclusions about how it formed and transformed over its life. Doing so required powerful electron microscopes and the use of spectrometers, which can provide details on the chemicals present in an object based on how the object reflects light.
The scientists conclude Ryugu likely formed after a huge rocky body in the early solar system was smashed into by another rocky body (The early solar system was pretty wild, so this was happening a fair bit). The material that was ejected during the collision eventually coalesced into the spinning-top asteroid we know as Ryugu because of gravity. This impact, according to the analysis, likely occurred around 2 million to 4 million years after the solar system formed. Based on the way the samples have been altered by water, the scientists believe they're from about 5 million years after the formation of the solar system.
"Everything happened in a very, very early timing [in regard to] the solar system formation," says Tachibana.
Since then, the asteroid has just been in hibernation mode, with little change to its composition. So... what does that all mean?
Why meteorites matter
To understand the importance of the samples, it's best to look at pieces of rock that have fallen to Earth. Scientists call these "meteorites."
Meteorites can be classified into distinct groups based on their composition and chemistry. The most rare type of meteorites scientists have seen are known as "CI chrondrites" -- since the 1800s, we've seen only five meteorites of this class fall to Earth. One of the most famous is the Orgueil fall, which occurred in France in 1864, and another is Ivuna, which was discovered in Tanzania.
"[U]nlike other meteorite groups, the chemistry of the CI chondrites hasn't evolved or been modified, and they can tell us about the initial composition of the solar system," says Ashley King, a scientist who leads the Mineral and Planetary Sciences Division at the Natural History Museum in the UK.
In a nutshell, CI chondrites are the most primitive rocks we've ever found. They come from a time when the solar system was just beginning to form. But the rocks that make it to Earth are altered by our atmosphere and the journey to the ground. When they smash into the atmosphere, they heat up and new minerals and chemicals are formed and then, when they land, they're altered by humidity and interactions with water.
When analyzing the CI chondrites, you might ask "what is naturally present in these rocks when they're in space and what has formed since arriving on Earth?" This has been something of a puzzle for meteoriticists, the scientists that specialize in studying meteorites, because -- until Ryugu -- we haven't had the ability to know what the chemical composition of an asteroid in space really is.
That's all changed with JAXA's analysis, and it's blowing some meteorite scientists away.
"I did read through the paper and my first reaction was "holy sh**!" said Gretchen Benedix, a planetary scientist at Curtin University in Western Australia.
"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," noted Benedix.
To sum it up, scientists now have access to the earliest epoch of our solar system and the implications for future study are profound. Think of it this way: JAXA scientists explored a meteorite that never made it to Earth and thus was never altered by the conditions on our planet. That's a monumental result.
"The Ryugu samples are the most chemically primitive extraterrestrial materials currently available to study and will lead to new breakthroughs in our understanding of the origin and evolution of planetary systems," says King.
This first paper is merely the beginning for JAXA scientists. Over the next few months, it's expected many more details about the samples from Ryugu will be revealed, unveiling details about the rock's magnetism, how it's been affected by space weathering and its exposure to the solar wind and cosmic rays.
What lies in wait for the scientists to discover? The possibilities are endless. Just this week, reports suggested JAXA had also discovered amino acids -- the "building blocks of life" -- in Ryugu. A full scientific report of Ryugu's amino acids is still to come, but this discovery adds to the notion that organic compounds may have been delivered to Earth from outer space.
As scientists across the world study the rock grains from Ryugu, and Bennu, our fuzzy understanding of the earliest time in solar system history will gradually come into focus. Potentially, it might even reveal where we come from. As we study the ancient space rocks, we could find the very stuff that makes us us may have been delivered on a rock billions of years ago.