Ryugu sample return

The Hayabusa2 spacecraft returned 5.4 g of material from the asteroid Ryugu. A first analysis of the samples found an estimated density of 1,282 ± 231 kg m⁻³, considerably lower than even the most porous meteorites. Together with preliminary spectral analysis, these results indicate that Ryugu is similar to CI chondrites, but darker, more porous and more brittle.

The MicrOmega imaging spectrometer performed a first characterization of the sample returned from asteroid Ryugu by Hayabusa2. Compositional homogeneity dominates down to millimetre scales, with signatures of hydrated phases and organics. At the submillimetre scale, NH-rich compounds and alteration products such as carbonates are detected.

The sample taken from carbonaceous asteroid Ryugu and brought back to Earth by the Hayabusa2 spacecraft contains outer Solar System-derived materials uncontaminated by terrestrial processes. Even CI carbonaceous chondrites, despite their closeness to solar abundances, are not pristine.

About 0.5% by volume of the Ryugu particle C0009 is made up of anhydrous silicates, mostly olivines, despite the extensive aqueous alteration of its parent body. Such aggregates, rich in ¹⁶O, were present in Ryugu’s protolith and survived fluid activity.

A comparison of copper and zinc isotopic measurements between the Ryugu samples and various carbonaceous chondrites excludes any genetic link between the two except for the CI (Ivuna-type) chondrites. Ryugu-like material might have accounted for ~5% of Earth’s mass.

Oxygen isotopic measurements from the Ryugu returned sample suggest that primitive hydrated carbonaceous chondrites are an important source of early water and other volatiles to Earth, despite being underrepresented in our meteorite collection due to their preferential destruction during atmospheric entry.

A close-up look at the action of space weathering on carbonaceous asteroids, provided by Ryugu’s returned samples, highlights its role on the dehydration of the first micrometre-thick layer of the surface, possibly hiding a water-rich interior. The depth of the 2.7 µm hydration band may be an indication of the level of space weathering withstood by a C-type asteroid.

The aqueous activity responsible for carbonate formation on Ryugu happened much earlier—less than 1.8 million years after CAI formation—than estimates (4–6 Myr) from carbonaceous chondrite meteorites. Ryugu’s parent body either was smaller than ∼20 km in diameter or was disrupted before reaching the high temperatures required.

MicrOmega characterized the population of carbonates detected in the bulk components and in individual grains of the Ryugu returned samples. Two main carbonate families are detected, which were likely formed via two distinct processes at different stages in the early Solar System.

The returned samples from Hayabusa2 show that C-type asteroid Ryugu experienced various steps of mineralogical alteration within only 1–2 million years after accretion.

The MASCOT lander observed a boulder on the surface of asteroid Ryugu up close. The boulder’s low thermal inertia is closer to fine regolith or comets rather than stony boulders, indicating high porosity and low tensile strength. Orbit measurements confirm that Ryugu’s surface is covered with similar boulders.

The Hayabusa2 team has discovered two types of bright boulder on the dark, carbonaceous asteroid Ryugu. One type has a spectrum consistent with material from an anhydrous silicate-rich asteroid, likely introduced by one or more collisions in Ryugu’s past.

The distribution of boulders on the surface of top-shaped asteroids such as Bennu or Ryugu tells us about the processes driving their evolution. A model shows that the spin-up induced by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect can explain simultaneously both the latitudinal behaviour of the boulders and the regolith migration.

Hayabusa2 created an artificial crater on Ryugu to analyse the subsurficial material of the asteroid. Results show that the subsurface is more hydrated than the surface. It experienced alteration processes that can be traced back to Ryugu’s parent body.

The Hayabusa2 spacecraft found dark boulders with very high porosity (>70%, as high as cometary nuclei) at the bottom of small craters on Ryugu. Such boulders are probably the most pristine parts of the planetesimals that formed Ryugu’s parent body and might have been captured by Hayabusa2 sampling.

Modelling shows that electrostatic lofting removes the finer particles from the asteroid regolith layer efficiently for kilometre-sized or smaller bodies, creating the boulder-dominated surfaces seen on Bennu or Ryugu. On larger bodies, the formation of fine regolith via weathering effects dominates instead.

Missions from various space agencies are going to be busy delivering material from different bodies throughout the upcoming decade, looking forward to the return of samples from Mars.

The first robotically obtained samples of a carbonaceous asteroid have been safely returned to Earth. A non-destructive first-look analysis shows that asteroid Ryugu may be a CI chondrite with interesting variations.

Samples returned from the carbonaceous (C-type) asteroid 162173 Ryugu by the Hayabusa2 mission were preliminarily analysed in a non-destructive manner. Their dark spectral features, small densities and absence of a high-temperature component imply that they are most similar to primitive CI group chondrites, but show some differences to known planetary materials.

The Hayabusa2 spacecraft will soon rendezvous with asteroid Ryugu in order to study its composition using remote sensing, a lander, rovers and sample return, explains Elizabeth Tasker.

On 27 June 2018 the Hayabusa2 spacecraft arrived at the carbonaceous asteroid Ryugu — a top-shaped asteroid with a very dark surface and many boulders. After a careful search for a safe and flat landing site, the first touchdown successfully took place on 22 February 2019.

The new generation of sample return missions from small bodies will deliver to us fresh witnesses from the early Solar System. In-depth laboratory analysis of retrieved samples will allow us to look in unprecedented detail at the formation and evolution of organic materials in asteroids.

NASA’s spacecraft OSIRIS-REx is planning to bring back a sample from a near-Earth asteroid in 2023, and it has just delivered its first scientific results. It is only one of the projects from various space agencies that will put small bodies and sample return into the spotlight in the upcoming decade.

The Hayabusa2 and OSIRIS-REx teams have unexpectedly found bright boulders on their respective dark asteroids, Ryugu and Bennu, which provide solid clues about the composition and origin of impacting bodies in their formation history.

The future of Solar System exploration lies in the subsurface of rocky bodies, including planets. Robots provide a relatively cost-effective and safe method of probing the subsurface; this Perspective summarizes recent efforts in robotic drilling and regolith-sampling methods, concluding with a summary of China’s future space exploration plans.

The exploration of small planetary bodies depends crucially on the success of anchoring robots. This Perspective takes us through the diverse challenges and technological innovations involved when making contact with unknown surfaces.