Comparing pieces of our past: grains from asteroid Bennu arrive from NASA
“We were lucky to return 121.6g of material, over twice the mission requirement,” said Dr Kathleen Vander Kaaden, NASA Chief Scientist for Astromaterials Curation. “And we are excited to share a portion of this sample with Japan.”
On August 22, 2024 JAXA and NASA scientists met for a joint press conference at the JAXA Institute of Space and Astronautical Science (ISAS). Placed on the table before the teams were two documents to formally acknowledge the delivery of 0.66g of extraterrestrial grains from asteroid Bennu to JAXA.
The OSIRIS-REx mission was launched by NASA on September 8, 2016. Similar to the JAXA Hayabusa2 mission that had departed almost two years earlier, the destination of OSIRIS-REx was a carbonaceous asteroid and the goal was to return a sample for analysis on Earth. Hayabusa2 had returned a sample from asteroid Ryugu in December 2020. OSIRIS-REx would bring back a sample from asteroid Bennu in September 2023. The two mission teams had worked closely together during both missions, and a Memorandum of Understanding (MOU) had been signed to exchange part of each sample within a year after a successful return to Earth. It is an exchange that will allow a world first comparative study between two different carbonaceous asteroids. The importance of such an arrangement can not be underestimated.
Analysis of the asteroid Ryugu sample has revealed a composition very similar to that of the Sun, indicating that the asteroid is a pristine record of some of the first solid material that formed in the Solar System. This makes Ryugu an ingredients list for forming our planets. Scientists around the world are studying the composition of the Ryugu sample to understand how planets began and evolved, including how the habitability of the Earth arose.
The importance of such a reference for planet building has led to the “Ryugu Reference Project” (RRP) to create a guide to the elemental and isotopic chemical abundances that started the Solar System, using the Ryugu sample as a basis. But this work would be undermined if asteroid Ryugu turned out to be an unusual outlier in early Solar System material.
“We do not know how unique these asteroids are,” explains Professor Usui Tomohiro, Astromaterals Research Group Manager at ISAS. “Are they unique within the early Solar System, or are they common throughout the early Solar System? A comparative study will answer this question.”
The MOU stated that NASA would receive 10% of the weight of the Ryugu sample in 2021, while JAXA would receive 0.5% of the weight of the Bennu sample in 2024. The discrepancy in percentage reflected the anticipated yield of the different sampling techniques employed by each mission. Hayabusa2 collected material from two different locations on asteroid Ryugu, employing a sampling mechanism that allowed for a variety of surface conditions by using a small 5g tantalum projectile to break up larger rocks. The mission threshold for success was 100mg of material. By contrast, the OSIRIS-REx “Touch and Go sample Acquisition Mechanism” (TAGSAM) technique used a pneumatic system with injection of nitrogen gas to collect material from a single site, but with a much larger mission requirement of 60g of sample. In the end, both missions exceeded expectations, with Hayabusa2 returned 5.4g from asteroid Ryugu and OSIRIS-REx returning a stunning 121.6g from asteroid Bennu. 0.54g of Ryugu grains were delivered to NASA in November 2021, and 0.66g of Bennu grains arrived at JAXA this month.
Return to Earth! Left is the re-entry capsule and parachute from Hayabusa2 where it was spotted in the Woomera desert in Australia, on the right is the sample return capsule from NASA’s OSIRIS-REx mission after landing at the Utah Test and Training Range. (OSIRIS-REx: NASA/Keegan Barber, Hayabusa: JAXA)
While meteorite studies must battle against contamination from Earth, extensive care was taken with both the samples collected from Ryugu and Bennu to keep the space-collected material free of Earth’s influence. After landing, both sample capsules were swiftly moved to nearby temporary clean room facilities. Gases were removed from the Hayabusa2 sample container, which was then vacuum sealed and placed in the highly unreactive pure nitrogen for the flight back to Japan. The OSIRIS-REx sample container was also connected to pure nitrogen after landing in Utah before making the trip to the NASA Johnson Space Center in Houston, Texas.
In addition to the OSIRIS-REx asteroid Bennu sample, the Johnson Space Center also houses cosmic samples from both the Hayabusa and Hayabusa2 missions, along with lunar, solar wind, cometary, cosmic dust, and meteorite samples. The JAXA asteroid samples from Hayabusa, Hayabusa2, and now OSIRIS-REx, are at the Extraterrestrial Sample Curation Center (ESCuC) on the JAXA Sagamihara Campus. A new cleanroom was opened this summer for the analysis and storage of the OSIRIS-REx Bennu sample. It is here that JAXA’s comparative study of the two asteroids will begin.
As with the asteroid Ryugu sample, JAXA will first perform an initial description of the sample from Bennu. This will measure the basic properties of individual grains and the aggregate sample as a whole, such as weight, size and appearance under a microscope, and the composition revealed through an infrared spectrometer (excellent at identifying water content and organic compounds). Several instruments have been updated from the equipment used to analyse the sample from asteroid Ryugu, but the analysis conditions have intentionally been kept the same to allow an accurate comparison.
“By analysing the samples from Ryugu and Bennu under almost identical conditions, JAXA should obtain data to more accurately compare the two samples,” explains Dr Yogata Kasumi, researcher in the Astromaterials Science Research Group.
The initial description is expected to take about four months, after which applications for further analysis will be open to the worldwide scientific community to expedite comparative research between the Ryugu and Bennu samples.
Hints as to what to expect can be found in the first analysis journal paper of the Bennu sample led by OSIRIS-REx PI Professor Dante Lauretta and Mission Sample Scientist Professor Harold Connolly. Like Ryugu, the Bennu sample shows evidence of aqueous alteration, indicating the little asteroid was once part of a larger asteroidal body that contained liquid water. The composition of Bennu so far seems similar to Ryugu, but not identical and with a higher carbon abundance. The task ahead for scientists is to explore these differences in more detail, with the opportunity to run identical tests on both samples. The results will be used to piece together the overlapping and distinct histories of the two asteroids, and what they might mean for the abundances of rock, water- and organic-rich compounds that might have arrived on the early Earth and set the course for the journey towards habitability.
During the signing of the documents confirming the exchange of the Bennu asteroid sample, NASA Astromaterials Curator Dr Francis McCubbin also passed a Japan flag to ISAS Director General Kuninaka Hitoshi, noting that this particular flag had flown on the International Space Station, a journey of over twenty million miles. It was another wonderful symbol of human achievement and the power of international partnership, although a small journey indeed compared to that of Hayabusa2 and OSIRIS-REx.
The partnership between NASA and JAXA sample return missions will extend to up-coming Martian Moons eXploration (MMX) mission to return a sample from Mars’s moon, Phobos. The JAXA-led mission will include instruments and sampling technology contributed by NASA and the returned sample will be also shared with the US space agency.
“The NASA-JAXA sample curation partnership is extremely valuable, and we’re looking forward to continuing to learn and expand our capabilities by working with each other,” concluded Vander Kaaden at the press briefing. “It’s critical for science to make these precious samples available to the world to study, and we know that JAXA’s extensive capabilities in this area will support an increased science return on these materials. We look forward to continuing collaborations and exploring the Solar System together. Thank you, and onto MMX!”
Further information:
JAXA Astromaterials Science Research Group website
NASA Astromaterials Acquisition and Curation Office website (external site)
OSIRIS-REx sample delivery signing and press briefing (YouTube: mainly in Japanese)
Asteroid Bennu samples arrive at JAXA’s Sagamihara campus! (ISAS web announcement)
The Hayabusa2 sample from asteroid Ryugu: 2 year summary (video)
7 differences between JAXA’s Hayabusa2 and NASA’s OSIRIS-REx Missions (video)