Scientists have begun to release the first findings from an analysis of a handful of dirt scooped from the surface of a speeding asteroid by Hayabusa2. What they discovered suggests that this asteroid is made of the same material that formed our sun four and a half billion years ago.
After a six-year journey, the daring Hayabusa2 spacecraft zinged back into Earth’s atmosphere in late 2020 and landed deep in the Australian outback. When researchers from the Japanese space agency JAXA opened it, they discovered its precious payload sealed and intact: a handful of dirt scooped from the surface of a speeding asteroid by Hayabusa2.
Scientists are now releasing the first results of their analysis of this extraordinary sample. What they discovered suggests that this asteroid is made of the same material that formed our sun four and a half billion years ago.
“Previously, we only had a handful of these rocks to study, and they were all meteorites that fell to Earth and were stored in museums for decades to centuries, changing their compositions,” said geochemist Nicolas Dauphas, one of three University of Chicago researchers who worked with a Japan-led international team of scientists to analyze the fragments. “It’s incredible to have pristine samples from space. They are eyewitnesses from parts of the solar system we have yet to explore.”
Usually, all we get to study asteroids is the pieces that are big enough to make it to the ground as meteorites. If you took this handful and dropped it in the atmosphere, it would burn up. You would lose it, and a lot of evidence about the history of this asteroid would go with it.
Andrew M. Davis
‘It’s spectacular’
Hayabusa2 landed on Ryugu, a moving asteroid, in 2018 and collected particles from above and below its surface. After orbiting the asteroid for a year and a half, it returned to Earth with a sealed capsule containing about five grams of dust and rock. Scientists all over the world have been waiting for this one-of-a-kind sample, which could help redefine our understanding of how planets evolve and how our solar system formed. Scientists are especially ecstatic because these particles would never have made it to Earth without the protective shield of a spacecraft.
“Usually, all we get to study of asteroids is the pieces that are big enough to make it to the ground as meteorites,” said UChicago geochemist Andrew M. Davis, another member of the analysis team. “If you took this handful and dropped it in the atmosphere, it would burn up. You would lose it, and a lot of evidence about the history of this asteroid would go with it.
“We really haven’t had a sample like this before. It’s spectacular.”
Davis, Dauphas, and UChicago colleague Reika Yokochi are all part of a team assembled to help Japanese researchers analyze the samples. Each part of the capsule’s contents is being rigorously studied. Yokochi is part of a team that is analyzing the gases that were trapped in the capsule or in the dirt. Dauphas and Davis are part of a team that is studying the chemical and isotopic compositions grains to reveal their history.
The first compilation of these results, reported in Science, reveal the makeup of Ryugu.
The rock resembles a type of meteorite known as a “Ivuna-type carbonaceous chondrite.” These rocks have a similar chemical composition to what we measure from the sun and are thought to date back to the early days of the solar system, roughly four and a half billion years ago – before the sun, moon, and Earth formed.
All that existed at the time was a massive, rotating cloud of gas. Scientists believe that most of that gas was drawn into the center and formed the sun. As the remnants of that gas-cooled and expanded into a disk, they transformed into rocks that still float around the solar system today; Ryugu appears to be one of them.
The fragments appear to have been soaked in water at some point, according to scientists. “Imagine a floating ice and dust aggregate that turned into a giant mudball when the ice was melted by nuclear energy from the decay of radioactive elements present in the asteroid when it formed,” Dauphas explained. Surprisingly, the rock itself appears to be relatively dry today.
They estimated that Ryugu was altered by water circulation only about five million years after the solar system formed, using radioisotope dating. These findings are particularly intriguing to researchers because they suggest that comets and some asteroids, such as Ryugu, formed under similar conditions.
“By examining these samples, we can constrain the temperatures and conditions that must have existed during their lifetimes and attempt to understand what happened,” Yokochi said. She compared the process to attempting to figure out how a soup was made without knowing the recipe: “We can take the soup and separate the ingredients, and try to tell how much it was heated and in what order based on their conditions.”
The scientists noted that a portion of the discovery will be set aside for future analysis with more advanced technology, similar to how we did with Apollo lunar samples.
“After we got moon samples from Apollo 50 years ago, our ideas about how the moon formed completely changed,” Davis said. “We’re still learning new things from them, because our instruments and technology have advanced.
“The same will apply to these samples. This is the kind of gift that keeps on giving.” This is the first of several international missions that will return samples from another asteroid named Bennu, as well as previously unexplored areas of our moon, Mars, and Mars’ moon Phobos. This should all happen within the next 10 to 20 years.
“It has flown under the radar for the general public and some policymakers, but we are entering a new era of planetary exploration that is unprecedented in history,” Dauphas said. “When our children and grandchildren visit museums, they will see returned fragments of asteroids, Mars, and hopefully other planets.”
