“They are stained glass windows to the earliest time period of the solar system,” says Harold Connolly, a cosmochemist with Rowan University in New Jersey, about the enigmatic origins of ancient chondrules delivered to Earth by Japan’s Hayabusa2 mission. “They are witnesses to processes that operated in the early solar system. The question is, what did they witness?”
A Building Block of Life?
“I hope this will shed light on how the solar system was formed and how water was brought to Earth,” said Hiroshi Yamakawa president, of Japan Aerospace Exploration Agency (JAXA), about retrieved samples from the distant diamond-shaped asteroid Ryugu– after a nearly 5.3-billion-kilometer trip –contained in the return toaster-sized capsule of the Hayabusa2 mission .The capsule, parachuted to a landing in the red desert sand of Woomera, Australia, harbors carbon-rich soil and rock fragments –clues about the ancient delivery of water and organic molecules to Earth. Awaiting teams of scientists located the capsule’s landing site with radar and rushed via helicopter to retrieve it.
From 2014 to Today
Launched in 2014 by the Institute of Space and Astronautical Science of JAXA, Hayabusa2 spent 18 months circling Ryugu, making remote observations, and releasing several tiny rovers that hopped on the surface gathering data. After identifying safe spots amid the boulders, reports JAXA, “the craft made two fleeting touchdowns to grab samples, once from the surface and again after blasting a crater to expose subsurface materials.”
A Cosmic “Treasure Box”
The Mission goal was to collect 100 milligrams of carbon-rich soil and rock fragments. The “treasure box” will be opened in clean room facilities in Tokyo this week. “We believe that a lot of material was collected,” JAXA Mission Manager Makoto Yoshikawa said in a recent briefing.
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 bombarded a proto-Earth billions of years ago, they may have helped deliver the building blocks of life, Yoshikawa said. “It could be that these organic materials were the sources of life on Earth.” The mysterious origins of chondrules—small seedlike rocks measuring up to just a few millimeters across,—may be revealed at last thanks in part to pristine material returned to Earth from Ryugu.
Enigmatic Chondrules –Life Everywhere?
Chondrules are thought to have formed some 4.5 billion years ago, shortly after the birth of our solar system. From there, they became embedded in larger rocks, called chondrites, which make up the majority of the roughly 64,000 meteorites that humans have discovered throughout recorded history. “Chondrules are everywhere,” says Fred Ciesla, a planetary scientist from the University of Chicago.
So far, reports Jonathan O’Callaghan for Scientific American, “no one has been able to explain this ingredient’s origins, yet the ramifications of doing so are tremendous. It may reveal to us not just some nebulous history of the solar system, but also never-before-seen details of the process by which our sun’s retinue of planets formed. In our understanding of how Earth—any planet in the cosmos, in fact—came to be, there may be nothing as important as the mystery of the chondrule.”
Scientists can date their formation to a window of a few million years 4.567 billion years ago by measuring the abundance of an isotope of aluminum they contain called aluminum-26, according to O’Callaghan. “This is a short-lived nuclide that only exists in the early solar system,” says Noriko Kita, an expert in meteorite aging from the University of Wisconsin-Madison.That advanced vintage, writes O’Callaghan, “makes chondrules the second-oldest recognizable objects in our solar system, after calcium-aluminum-rich inclusions (CAIs), specks of white in meteorites that are thought to have formed one to three million years earlier by condensing out of the gas that surrounded our young sun”.
Water-Bearing Minerals are Ubiquitous
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. But distinguishing biomolecules due to earthly contamination from pristine organics in the asteroid samples is “very difficult,” says Seiji Sugita, a planetary scientist at the University of Tokyo. “The Ryugu samples brought by Hayabusa2 are as Earth-contamination-free as it can get,” he says.
The abundance of water in Ryugu will help determine how much water asteroids delivered to Earth billions of years ago, says Sugita. Oddly, 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. But we need a definite answer from sample analysis.”
Gave Prebiotic Chemistry on Ancient Earth a Boost
“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 reports Science. 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.”
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.
NASA –Destination Bennu
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, reports Science. “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.”
Image credits: JAXA and top of page, Shutterstock License