To date, there have been three missions to collect samples from asteroids and bring this material back to Earth: the Hayabusa and Hayabusa2 missions led by JAXA, and the OSIRIS-REx mission led by NASA. The three asteroid samples are being studied in laboratories around the world to investigate the origin of our planets, the development of habitability, and to better understand the structure of these small celestial bodies in case humanity one day needs to protect the Earth from a fatal impact.
The first review paper of all three missions was published in the academic journal, "Contemporary Physics", giving an overview of each exploration and highlighting several of the key scientific discoveries so far revealed.
A tale of three missions
On 13 July 2010, the JAXA Hayabusa mission returned to Earth carrying a sample gathered from an asteroid. Severely damaged after being struck by a massive solar flare, the spacecraft successfully released the protective re-entry capsule before burning up in the Earth's atmosphere. The capsule landed safely in the southern Australian desert, bringing home the first pristine material from the small bodies of our Solar System: a time capsule of tiny grains from when the Earth was just beginning to form.
Billions of years of geological, chemical and sometimes biological activity has erased the starting conditions and early evolution of the planets. To probe what material initially formed the planets, and explore how this starting point might have led to life on Earth, we need to seek out celestial bodies that formed at the very start of this process and which were too small to do... much of anything else.
However, asteroid sample return missions are some of the most technically demanding robotic exploration attempted by humanity. Very little of an asteroid's surface properties can be determined from observations from Earth, meaning that the complex operations required to collect a sample has to be designed without any knowledge of the landing area. The landing and acquisition sequence must also be conducted autonomously, due to the distances involved incurring long communication times, and the spacecraft must make a complete round-trip to return the sample to Earth that greatly extends the mission operation time. When the sample capsule is finally delivered to Earth, a second fight begins to protect the pristine asteroid grains from contamination from our planet's extremely vibrant biosphere.
The three asteroid sample return missions so far flown also met unexpected challenges. Hayabusa was struck by one of largest solar flares in recorded history, causing damage to the spacecraft that led to significant technical difficulties over the journey to and from asteroid Itokawa. Hayabusa2 arrived at asteroid Ryugu to find a surface far more rugged than anticipated, forcing the team to redesign the landing operation so that the spacecraft could touchdown in a far smaller region than originally planned. OSIRIS-REx felt the surface give way as the spacecraft descended to collect material, causing a drop of almost half a meter into asteroid Bennu.
Despite these difficulties, the observations made by the spacecraft of the asteroids' global properties, coupled with the detailed analysis possible from the retrieved samples, have revealed a history of three small celestial bodies that probes both the evolution of small and large celestial worlds.
The JAXA Hayabusa mission (sample return 2010)
Figure 1: The history of asteroid Itokawa as discovered by the Hayabusa mission (from Tasker et al. 2026, Figure 6).
The destination of Hayabusa was asteroid Itokawa, an S-type near Earth object with an orbit between Mars and the Earth. Upon arrival, Hayabusa did not find a monolithic body but a rubble pile, consisting of loosely accumulated fragments that had coalesced after a catastrophic collision. Although "rubble-pile asteroids" had previously been suspected, this was the first direct evidence of their existence.
The sample from Hayabusa confirmed that S-type asteroids matched LL chondrite meteorites. Due to the difficulties in comparing the very different data collected from ground-based observations of asteroids and laboratory analysis of meteorites, it is challenging to match meteorite material with asteroid types. The sample grains returned from Itokawa was the first confirmation of the link between the celestial and Earth-bound rocks.
Notably, connecting S-type asteroids and LL chondrites had been further inhibited by S-type asteroids showing a spectrum (the different wavelengths of the reflected light) that seemed redder than LL chondrites. Examination of the sample returned from Itokawa showed that this was due to "space weathering", whereby the surface of the asteroid is affected by solar radiation, the solar wind (high-energy particles streaming from the Sun), and cosmic rays. Space weathering occurs on airless bodies without atmospheres to protect their surface. The effect had previously been observed on the Moon, but this was the first evidence of how space weathering works on an asteroid.
The Itokawa sample showed evidence of intense heating, up to temperatures of 800°C. The asteroid's minerals had therefore been thermally altered, evaporating away any volatile material that might have been present when the material first formed. The most likely source of such heating is the radioactive decay of Aluminium-26 (Al-26), which was abundant in the early Solar System. The present-day rubble-pile Itokawa must once have been part of a larger parent asteroid that formed around two million years after the start of the Solar System, early enough to have accreted plenty of Al-26 and become very hot as this short-lived radioactive isotope decayed. However, not all early planet-building material met this fate. The temperatures reached depended on the size of the first asteroid, and exactly when it formed. Other types of asteroid might therefore have quite different histories. So with the technical abilities to collect an asteroid sample now established, JAXA launched the Hayabusa2 mission.
The JAXA Hayabusa2 mission (sample return 2020)
Figure 2: The history of asteroid Ryugu as discovered by the Hayabusa2 mission (from Tasker et al. 2026, Figure 13).
The destination of Hayabusa2 was the C-type asteroid, Ryugu. Like asteroid Itokawa, Ryugu proved to be a rubble pile, indicating that the asteroid had once been part of a much larger body that had undergone a major disruption.
Further evidence of a larger parent was found in the sample, which was discovered to be packed with hydrated minerals that contain the hydroxyl group (-O-H) or water molecule (H-O-H) as part of their structure. Hydrated minerals require water to form, but Ryugu's current size is too small to host liquid water. The asteroid minerals must therefore have formed when Ryugu was part of a larger parent asteroid.
Unlike Itokawa, the sample from Ryugu showed no evidence of heating above 100°C. The sample composition included both refractory and volatile elements, and was a close match to both the Sun and a rare class of meteorite known as CI chondrites. Only ten CI chondrites have ever been found on Earth, yet C-type asteroids like Ryugu appear to be common in space. This suggests that most CI chondrites burn up in our atmosphere, and only the rarer but tougher asteroid types make it to the ground. The result is a strong bias in our meteorite samples, emphasising the importance of sample return to learn about more typical planet-building material.
Surprisingly, tiny inclusions of liquid were found embedded in the sample grains. Analysis revealed a composition of water and carbon dioxide. For these to be included in Ryugu, the asteroid must have formed where both water and carbon dioxide could exist as solid ice. Ryugu's parent asteroid therefore formed far out in the Solar System, and was scattered inwards toward the terrestrial planets. This demonstrates a possible delivery mechanism for water on Earth, with asteroids similar to Ryugu forming hydrated minerals in the ice-laden outer Solar System and bringing this water to the inner planets.
But Ryugu's water-rich grains were a surprise. Observations by the spacecraft suggested the asteroid was lacking in water. This proved to be due to space weathering, which has created a dehydrated cloak on the asteroid surface, concealing the inner water-rich composition. Observations of asteroids from Earth or from spacecraft may therefore underestimate the volatiles present in these small worlds.
The Ryugu sample did not just carry water-rich minerals, but also a plethora of organics. These included many molecules needed by life on Earth, including amino acids and all five of the primary nucleobases that form the base sequences of RNA and DNA. It is therefore possible that packages of the key ingredients for habitability are formed regularly in the cold regions of planetary systems, and can be transported inwards to temperate rocky planets as a key step to a habitable world.
Hayabusa2 collected two samples from different locations on Ryugu. However, there was the possibility that the asteroid was anomalous, and it was rare that such organic and water rich material formed in the Solar System. What was needed was a comparison.
The NASA OSIRIS-REx mission (sample return 2023)
Figure 3: The history of asteroid Bennu as discovered by the OSIRIS-REx mission (from Tasker et al. 2026, Figure 17).
Launched less than two years after Hayabusa2, the NASA OSIRIS-REx mission team and the JAXA team joined forces. A Memorandum of Understanding (MoU) was signed by the two space agencies that included the exchange of three mission co-investigators, and a sample exchange of the delivered grains from Ryugu and the target of OSIRIS-REx, asteroid Bennu.
Asteroid Bennu is classified as a B-type asteroid, a class that shows strong observational similarities with C-type asteroids such as Ryugu. It was hoped that Bennu would also comprise of material that has not experienced strong thermal changes. The MoU between the two teams would therefore enable the first comparative analysis between two examples of pristine asteroids.
Bennu was discovered to be a third rubble pile, with strong evidence of having once been part of a larger parent asteroid that had hosted liquid water. The chemistry of Bennu is more nitrogen-rich than Ryugu, but the asteroid was also packed with hydrated minerals and organics, including the life-essential amino acids and nucleobases.
Bennu also showed evidence of having hosted brines, created as water partially evaporated to produce a solution enriched in dissolved solids. Brines encourage the precipitation of highly-soluble salts, which have also been seen on Ceres and Enceladus. Bennu may be a precursor to such icy worlds, giving clues to organic packages that have been delivered and possibly developed beyond the Earth.
Bennu has also experienced space weathering, but despite hosting a similar composition at Ryugu, the asteroid surface showed a different change in colour. This might be a later stage of space weathering, and the variety is important to understand when interpreting ground-based observations of asteroids.
OSIRIS-REx also studied the trajectory and structure of Bennu to better predict the asteroid's future path. Like Itokawa and Ryugu, Bennu is a near-Earth object. The asteroid is classified as "potentially hazardous", with a probability of a future collision with the Earth. Results from OSIRIS-REx confirmed a cumulative probability of just 0.057% of an impact through the year 2300.
The future
2026 is a big year for small body exploration and sample return. This fiscal year, JAXA will launch the Martian Moons eXploration (MMX) mission. MMX will visit the two moons of Mars, Phobos and Deimos, and collect a sample from Phobos to return to Earth. While not on asteroid-like orbits, the two moons are also small celestial bodies that may have been formed during a giant impact with Mars, or be asteroids that were snagged by Mars's gravity. The mission will investigate the composition of the moons to understand their formation process, and the movement of water and organics through the Solar System as the planets developed.
Longer term, a sample return from a comet is being considered by both JAXA (Next Generation small-body Sample Return Mission, NGSR) and NASA. Comets formed in the Kuiper Belt or Oort cloud, and are considered the least altered building blocks in the outer Solar System. Returning a comet sample will be a new challenge, as the volatile-rich material must be preserved over the long return journey. Meanwhile, the ESA-led Comet Interceptor mission will launch in 2029, with involvement from JAXA. While the mission will not return a sample, it will rendezvous with a long-period comet or possibly interstellar object for remote analysis.
After delivering the sample from Ryugu to the Earth, Hayabusa2 returned to deep space on an extended mission. Now referred to as the Hayabusa2 Small Hazardous Asteroid Reconnaissance Probe (Hayabusa2#), the mission will first attempt a flyby observation of asteroid Torifune on 5 July, 2026. A flyby requires a high precision close approach which will test the trajectory control relevant for planetary defence manoeuvres.
In 2022, the NASA DART mission tested just such a manoeuvre in an intentional collision with asteroid Didymos. In November this year, the ESA-led Hera mission (carrying a thermal imager designed by JAXA) will arrive at Didymos to better understand the outcomes of kinetic deflection techniques.
A big opportunity to gather more information for planetary defence will arrive in the form of asteroid Apophis, which will make an unprecedented close approach to the Earth in April 2029. The asteroid will be observed by OSIRIS-REx, which will rendezvous with Apophis shortly after the asteroid's close approach for the spacecraft's extended mission, OSIRIS-APEX. Prior to reaching the Earth, Apophis will also be observed during a flyby exploration by JAXA's DESTINY+ mission, and then accompanied through the approach to Earth by the ESA/JAXA Ramses mission.
These international teams will observe how the proximity of the Earth affects the structure and trajectory of an asteroid, and explore how we might deflect such an object on a collision course. Together, we are collecting information in case we need to protect our existence against the small bodies that may have begun it.
Publication information:
Title: The science from asteroid sample return missions
Journal: Contemporary Physics
Authors: E. J. Tasker, H. C. Connolly Jr, S. Tachibana
DOI: 10.1080/00107514.2026.2646056
