Between 2014 and 2020, Japan’s space agency sent a spacecraft the size of a large refrigerator to a diamond-shaped asteroid, blasted a crater into its surface, and carried home the material that flew out. The mission, Hayabusa2, returned the first samples ever collected from beneath an asteroid’s surface — rock that had been shielded for eons from the harsh weathering of open space. Those pristine grains, delivered to Earth in a small capsule in December 2020, gave scientists a chemically unaltered look at the building blocks left over from the birth of the solar system.
A rubble pile called Ryugu
The destination was asteroid 162173 Ryugu, a dark, carbon-rich body roughly 900 meters across that spins with a distinctive spinning-top shape. Ryugu is not a solid boulder but a loosely bound pile of rubble, a heap of rock and dust held together by weak gravity. That composition made it a prime scientific target: carbonaceous asteroids are thought to preserve some of the oldest and least-altered material in the solar system, including water-bearing minerals and carbon compounds. Hayabusa2 launched in December 2014, arrived at Ryugu in mid-2018, and spent more than a year surveying the surface before attempting to grab a piece of it. During that survey the spacecraft dropped a set of tiny hopping rovers and a European-built lander onto Ryugu, which returned the first pictures ever taken from the surface of an asteroid. Those images revealed a landscape strewn with boulders and almost entirely lacking the fine, sandy dust many scientists had expected.
Firing a copper projectile into an asteroid
To reach material that the Sun and cosmic rays had never touched, the mission had to dig. On April 5, 2019, Hayabusa2 released a device called the Small Carry-on Impactor, which fired a two-kilogram copper slug into Ryugu at high speed while the spacecraft ducked behind the asteroid to shelter from flying debris. The strike carved out an artificial crater more than 10 meters wide — the first artificial crater deliberately formed on an asteroid — and flung buried rock across the surface, exposing pristine subsurface grains for collection.
The second touchdown that grabbed buried grains
Reaching the exposed material demanded pinpoint flying. On July 11, 2019, Hayabusa2 descended a second time and briefly touched down near the fresh crater, firing a small projectile into the surface to kick up particles that were funneled into a collection horn. Because that spot had been excavated from below, the grains it captured had spent their existence sealed inside the asteroid, protected from the space weathering that darkens and chemically alters exposed surfaces. The boulder-strewn ground left almost no flat, safe area to land, so engineers dropped a reflective target marker onto the surface in advance and narrowed the touchdown zone to a patch only a few meters wide, threading the spacecraft into it. The maneuver made Hayabusa2 the first mission to collect subsurface material from an asteroid, a feat its mission record documents alongside the earlier surface sampling.
A capsule in the Australian outback
With its samples sealed inside, the spacecraft began the long journey home. On December 6, 2020, Hayabusa2 released a small return capsule that streaked through the atmosphere and parachuted to a soft landing in the Woomera desert of South Australia, while the mothership itself flew on toward a new target. When curators opened the sealed container, they found more than five grams of dark rock and dust — a haul that vastly exceeded the mission’s minimum goal of 0.1 gram — along with the first gas sample ever brought back from an asteroid. NASA’s astromaterials curation team, which received a share of the material, catalogs the returned Ryugu sample for study by laboratories worldwide.
Why buried grains are scientifically priceless
An asteroid’s outer skin is a poor record of its origins. Constant bombardment by solar particles, micrometeorites, and cosmic radiation slowly bakes and reshuffles the surface, erasing the chemistry that was present when the body first formed. Material from below the surface escapes that damage, preserving a purer snapshot of the early solar system. Analyses of Ryugu’s grains found water-bearing minerals and a rich inventory of organic molecules, including compounds relevant to the chemistry of life, and confirmed that the asteroid ranks among the most primitive objects ever examined in a laboratory, according to peer-reviewed analysis of the returned volatiles.
Ryugu as a time capsule for the solar system
The scientific value of the mission comes from the pairing of two things that are rarely available together: material that formed at the dawn of the solar system, and knowledge of exactly where in space it came from. Meteorites that fall to Earth are altered by their fiery passage through the atmosphere and by exposure to the ground, and their parent bodies are usually unknown. Ryugu’s grains carry no such uncertainty. By drilling to the asteroid’s interior and delivering the results intact, Hayabusa2 turned a distant rubble pile into a controlled sample of the raw ingredients from which the planets — and eventually life — were assembled. The approach set the template that later sample-return missions have followed: NASA’s OSIRIS-REx delivered pieces of a different carbon-rich asteroid, Bennu, to Earth in 2023, and comparing the two hauls lets researchers test which chemical traits are common to such bodies and which are unique. Hayabusa2, having released its capsule, did not stop; the spacecraft continued on an extended mission toward yet another asteroid, still flying years after its samples reached the ground.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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