After a six-year journey, a brave spacecraft named Hayabusa2 returned to Earth’s atmosphere in late 2020 and landed deep in the Australian outback. When researchers from the Japanese space agency JAXA opened it, they found its precious cargo sealed and intact: a handful of earth that Hayabusa2 managed to collect from the surface of a running asteroid.
Scientists have now begun to announce the first results of the analysis of this extraordinary sample. What they found suggests that this asteroid is a piece of the same substance that merged into our sun four and a half billion years ago.
“Previously we only had a handful of these rocks to study, and all of them were meteorites that had fallen to Earth and kept in museums for decades or centuries, which changed their composition,” said geochemist Nicolas Dauphas, one of the three Universities of Chicago researchers who worked with an international team of scientists led by Japan to analyze the fragments. “Having pristine samples from space is just incredible. They are witnessing parts of the solar system that we would not otherwise have explored.”
In 2018, Hayabusa2 landed on a moving asteroid called Ryugu and collected particles from above and below its surface. After spending a year and a half in orbit around the asteroid, he returned to Earth with a sealed capsule containing about five grams of dust and rock. Scientists around the world have eagerly awaited the unique sample, which could help redefine our understanding of how planets evolve and how our solar system was formed.
Scientists are particularly excited that these particles would never have reached Earth without the protective barrier of a spacecraft.
“Usually, all we can study about asteroids are the pieces that are large enough to land as meteorites,” said UChicago geochemist Andrew M. Davis, another member of the analysis team. “If you took this handful and dropped it into the atmosphere, it would burn. You would lose it and a lot of evidence about the history of this asteroid would go with it.
“We’ve never had a champion like this before. It’s spectacular.”
Davis, Dauphas and UChicago colleague Reika Yokochi are all part of a team brought together to help Japanese researchers analyze the samples. Each part of the contents of the capsule is rigorously studied. Yokochi is part of a team that is analyzing gases that have been trapped in the capsule or in the mud. Dauphas and Davis are part of a team that is studying the chemical and isotopic compositions of grains to reveal their history.
The first compilation of these results, shown in Science on June 9, reveals Ryugu’s makeup.
The rock is similar to a class of meteorites known as “Ivuna-type carbonaceous chondrites”. These rocks have a chemical composition similar to what we measure from the sun and are thought to date back to the beginning of the solar system about four and a half billion years ago – before the formation of the sun, moon and Earth. [should Moon be capitalized to distinguish it from other moons?]
Back then, all that existed was a giant spinning cloud of gas. Scientists think most of that gas was drawn to the center and formed the star we know as the sun. When the remnants of that gas expanded into a disk and cooled, it turned into rocks, which still float around the solar system today; it seems Ryugu may be one of them.
Scientists said the fragments show signs of being submerged in water at some point. “Imagine an aggregate of ice and dust floating in space, which turned into a giant ball of mud when the ice was melted by nuclear energy from the decay of radioactive elements that were present in the asteroid when it formed.” Dauphas said. But surprisingly, the rock itself appears to be relatively dry today.
Using radioisotope dating, they estimated that Ryugu was altered by water circulation only about five million years after the solar system was formed.
These results are of particular interest to researchers because they suggest similar formation conditions between comets and some asteroids such as Ryugu.
“By examining these samples, we can limit the temperatures and conditions that must have occurred during their lifetime and try to understand what happened,” explained Yokochi.
He likened the process to trying to figure out how a soup was made, but with only the end result rather than the recipe: “We can take the soup and separate the ingredients, and try to figure out from their condition how much it was heated and in what order.”
Scientists have noted that a percentage of the find will be set aside so that they can be analyzed in the future with more advanced technology, just like we did with the Apollo lunar samples.
“After receiving moon samples from Apollo 50 years ago, our ideas about how the moon formed have changed completely,” Davis said. “We are still learning new things from them, as our tools and technology are advanced.
“The same will be true of these champions. This is a gift that continues to give.”
This mission is the first of several international missions that will bring back samples from another asteroid called Bennu, as well as unexplored areas on our moon, Mars and Phobos, the moon of Mars. All of this is expected to happen in the next 10-20 years.
“It has been very hidden from the public and some decision makers, but we are entering a new era of planetary exploration that is unprecedented in history,” said Dauphas. “Our children and grandchildren will see fragments of asteroids, Mars and hopefully other planets returned when they visit museums.”