Japan has once again retrieved samples from a distant asteroid, which scientists will scrutinize for clues about the ancient delivery of water and organic molecules to Earth. The return capsule of the Hayabusa2 mission—about the size and shape of a wok—parachuted to a landing in the red desert sand of Woomera, Australia, in the early morning of 6 December, after a nearly 5.3-billion-kilometer trip to the asteroid Ryugu. A helicopter team homed in on a radio beacon and found the capsule intact.
Launched in 2014 by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency (JAXA), Hayabusa2 spent 18 months circling Ryugu, making remote observations of the diamond-shaped rubble pile. It also released several tiny rovers that hopped on the surface gathering data. After identifying safe spots amid the boulders, the craft made two fleeting touchdowns to grab samples, once from the surface and again after blasting a crater to expose subsurface materials. The goal was to collect 100 milligrams of carbon-rich soil and rock fragments. Just how much material was collected won’t be known until the sample container—the “treasure box”—is opened in clean room facilities in Tokyo this week. But by studying videos of the sample collection, “we believe that a lot of material was collected,” JAXA Mission Manager Makoto Yoshikawa said in a recent briefing.
In 2010, the original Hayabusa mission became the first to return material from an asteroid to Earth, after a visit to the asteroid Itokawa. Planetary scientists are interested in asteroids because they hold primordial material present during the formation of the Solar System 4.6 billion years ago that was not altered by the heat and pressures of processes on planets. Ryugu is a carbonaceous, or C-type, asteroid, which are thought to contain both organic materials and hydrates—minerals rich in chemically bound water. When similar asteroids pummeled a proto-Earth billions of years ago, they may have helped kick-start life by delivering the building blocks, Yoshikawa said. “It could be that these organic materials were the sources of life on Earth.”
Remote observations of Ryugu already indicate “that water-bearing minerals are ubiquitous,” and that the surface holds a “significant amount of organic materials,” says Sei-ichiro Watanabe, a planetary scientist at Nagoya University and Hayabusa2 project scientist. Analyses in terrestrial labs will identify the hydrated minerals and organic molecules, providing clues as to when and how they were formed.
Seiji Sugita, a planetary scientist at the University of Tokyo, says determining the abundance of water in Ryugu will help determine how much water asteroids delivered to Earth billions of years ago. But there is a puzzle: Ryugu appears to carry far less water than the otherwise similar asteroid Bennu, which is the target of a NASA sample return mission. “We have a couple of promising hypotheses on why and how Ryugu or its parent body lost or failed to gain water,” says Sugita, a Hayabusa2 team member. “But we need a definite answer from sample analysis.”
As for the origin of life, there is little support for the idea that asteroids actually seeded life itself, says Jonti Horner, an astrobiologist at the University of Southern Queensland, Toowoomba, who is not affiliated with the Hayabusa2 mission. But carbon-rich meteorites, hailing from asteroids similar to Ryugu, show chemistry on these primordial bodies may generate amino acids and even RNA—which could have given prebiotic chemistry on ancient Earth a boost. “That’s why people are very interested in looking at what the very primitive material on asteroids like Ryugu actually contains,” Horner says. But distinguishing biomolecules due to earthly contamination from pristine organics in the asteroid samples is “very difficult,” Sugita says. “The Ryugu samples brought by Hayabusa2 are as Earth-contamination-free as it can get,” he says.
After releasing the sample return capsule into Earth’s gravitational grasp, Hayabusa2 skipped away and will continue on to a 2031 rendezvous with the asteroid 1998 KY26. Mission planners decided it was the most scientifically interesting asteroid Hayabusa2 could reach and study, given remaining fuel, Yoshikawa said. The tiny 30- to 40-meter-diameter body appears to rotate once every 10 minutes.
Meanwhile, NASA’S OSIRIS-REx mission is due to return samples from asteroid Bennu in September 2023. JAXA and NASA have agreed to swap samples from their respective missions. Together with the Itokawa samples, researchers will be able to compare samples from three asteroids. “We’ll be able to learn a lot more about the Solar System’s past than we ever could by just visiting one of them,” Horner says. “It’s going to be a really interesting few years as we see the results these missions yield.”