NASA’s OSIRIS-REx mission embarked on a groundbreaking journey, marking the first attempt to retrieve a sample from an ancient asteroid, Bennu. This mission – the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer – is a seven-year long voyage that just delivered to Earth a pristine asteroid sample.
We last reported on NASA’s OSIRIS REx mission in the November 2021 EXPLORER after the spacecraft sampled asteroid 101955 Bennu and began its return. The recent arrival of its sample to Earth is an opportunity to go into more depth on the mission and compare it to another asteroid sampling mission to Bennu’s twin, carbonaceous asteroid 162173 Ryugu. Japan’s JAXA Hyabusa2 mission returned its samples almost three years ago. These missions are the first to visit carbonaceous asteroids.
Asteroids fit into three broad types:
- C for dark carbonaceous objects
- S for stony (siliceous) objects
- U for those which did not fit into either C or S
Asteroids are assigned a type and often a sub-type based on spectral shape, color and, sometimes, albedo, or reflectivity. These types correspond to an asteroid’s surface composition. The asteroid spectral shape can be compared to spectra of meteorites of known composition. C-type asteroids are the most primitive, pristine and common variety, forming about 75 percent of known asteroids. They are rich in volatiles and have a very low albedo because they contain a large amount of carbon, along with siliceous rocks and minerals plus nickel and iron metals.
Asteroid Bennu is a spectral B-type asteroid, a subtype of the wider C-group of carbonaceous asteroids. Bennu has an average diameter of approximately 1,611 feet. Some of these carbonaceous asteroids display indications of early aqueous alteration, and they may have incorporated significant amounts of water ice and organic carbon. The study of Bennu will provide valuable insights into the earliest solar system and the formation of celestial bodies.
The Epic Journey
OSIRIS-REx began its monumental voyage with a successful launch on Sept. 8, 2016, from Cape Canaveral Air Force Station atop an Atlas V rocket.
About a year after launch, OSIRIS-REx conducted an Earth-gravity-assist maneuver to gain momentum from our planet’s gravity, utilizing it as a slingshot to increase its velocity and fine-tune its trajectory towards Bennu.
After a journey covering millions of miles, on Dec. 3, 2018, OSIRIS-REx reached its destination, the asteroid Bennu. This was a crucial phase in the mission as the spacecraft entered a quasi-orbit around the primitive celestial body with extremely low gravity. Adjusting and maintaining the spacecraft’s distance from Bennu required constant vigilance and tweaks.
OSIRIS-REx spent more than a year surveying Bennu, mapping its surface in detail, and selecting a suitable site for sample collection. The mission team meticulously analyzed the asteroid’s topography and composition to identify a safe and scientifically valuable sampling location.
The most critical operation of the mission occurred on Oct. 20, 2020, when OSIRIS-REx executed the “touch-and-go” sample collection maneuver. The spacecraft descended to Bennu’s surface, briefly touched down while firing a burst of nitrogen gas to stir up regolith, collecting samples in a specialized container. This daring maneuver aimed to retrieve at least 2.1 ounces and potentially more asteroid material.
After the TAG event, OSIRIS-REx successfully stowed the sample container on Oct. 28, 2020 into a secure sample return capsule compartment within the spacecraft. This ensured that the collected material remained protected during the spacecraft’s journey back to Earth.
The SRC is a blunt-nosed cone, 81 centimeters in diameter and 50-centimeters tall and comprises five principal components: the heat shield, back shell, sample canister, parachute system and avionics. The total mass of the capsule is about 100 pounds (on Earth, that is).
The SRC first came into action after the collection of the sample, when a camera confirmed that a sufficient amount of material was present within the sample head. At that point, the hinged-forward heat shield opened up on a clamshell mechanism to allow the sample arm to place the entire sampling head into the capsule where it locks in place. Images captured during the stowage sequence reveal that a few particles managed to escape during the procedure. However, the team expressed confidence that a substantial amount of material remained secure.
Notably, a mylar flap – intended to retain the sample – seemed to be wedged open by larger rocks. With the head now securely stowed inside the SRC, the risk of further sample loss had been mitigated. Subsequently, the capsule was closed and sealed in preparation for the journey back to Earth.
The TAGSAM arm motion torque calculation indicated a sample mass of some 8.8 ounces – perhaps four times what was planned. A more precise mass estimate awaits the opening of the TAGSAM at NASA’s Astromaterials Acquisition and Curation Office at the Houston Johnson Space Center.
Having accomplished its primary objectives at Bennu, OSIRIS-REx bid farewell to the asteroid and on May 10, 2021, initiated its long journey back to Earth. The spacecraft left Bennu’s orbit, carrying with it the precious cargo of pristine asteroid samples.
Triumphant Return
OSIRIS-REx completed its return journey to Earth on Sept. 24, 2023, delivering the collected samples back to our planet. The SRC made a high-speed re-entry into Earth’s atmosphere at 27,000 miles per hour! A parachute brought it to a soft landing right on target in a designated recovery site in the Utah Test and Training Range in the desert of western Utah.
A helicopter transferred the SRC to a hangar at the Range and moved it into a clean room for partial disassembly. Clean room staff found a bonus treasure trove of loose asteroid particles, from fine dust to pebbles, inside the capsule but outside of the Sample Head. They were collected in aluminum cups for transfer to JSC for preliminary analysis. The sample canister, along with disassembled capsule components and environmental samples from Utah, was transported to NASA’s Johnson Space Center in Houston the next day. The TAGSAM waits to be opened in a special clean room at JSC. That process has been very methodical to avoid contamination and losing any of the precious samples.
Meanwhile, preliminary analysis of the loose bonus particles proceeded and was revealed at a NASA live webcast on Oct. 11, where the world got its first look at the bonus samples. These varied rocks, rich in carbon and organic content, align with the team’s expectations. In an initial assessment conducted by the Carnegie Institute of Science, a small test sample measured a carbon content of 4.7-percent – greater than most carbonaceous chondrite meteorites. NASA sample team lead analyst Daniel Glavin, responded, “Wow! OMG! This is the highest bulk carbon Carnegie has analyzed from any extraterrestrial sample. This is a unique sample we’re dealing with. We picked the right asteroid. And not only that, we brought back the right sample. This stuff is an astrobiologist’s dream.”
Further examination using ultraviolet analysis detected organic globules within the dust grains. Electron microscope analysis unveiled the presence of water-bearing clay minerals, sulfur and iron particulates. X-ray tomography analysis also identified sulfide minerals. The discovery of water-bearing clays is particularly intriguing, as scientists hypothesize that asteroids like Bennu might have played a crucial role in delivering water and organic materials to early Earth.
Further investigation is required to comprehend the detailed composition of the rocky materials from Bennu, yet the initial findings are optimistic. The presence of water and carbon in this celestial body suggests a potential explanation for the original delivery of water to Earth. Dante Lauretta, principal investigator of the OSIRIS-REx mission, and professor of planetary sciences and cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory, suggests that asteroids like Bennu might have played a crucial role in the emergence of life on our planet.
Over the next two years, the scientific team of the mission will continue the process of characterizing the samples and conducting the necessary analyses to fulfill the mission’s scientific objectives. NASA intends to preserve a minimum of 70 percent of the collected sample at Johnson Space Center for future research, perhaps using techniques unknown today. As a component of OSIRIS-REx’s scientific initiative, more than 200 scientists worldwide, including researchers from various U.S. institutions and international partners such as the Japan Aerospace Exploration Agency and the Canadian Space Agency, will explore the properties of the regolith. Furthermore, additional samples will be loaned to the Smithsonian Institution, Space Center Houston and the University of Arizona for public display later this fall.
What Do the Twin Asteroids Tell Us?
Asteroid Bennu is a B-type asteroid classified by the spectrum of its reflected light. Its surface reflects only about four percent of incoming sunlight, indicating high carbon content. This makes it exceptionally dark compared to other celestial bodies. Bennu has been relatively undisturbed for billions of years, maintaining its primitive composition. It is estimated to have formed in the first 10 million years of the solar system’s history – more than 4.5 billion years ago. It is classified as a “rubble-pile” asteroid composed of rocky debris loosely held together by weak gravity. It likely originated from the breakup of a larger parent asteroid, resulting in a structure with 20 to 40-percent porosity.
There is a 1-in-2,700 chance of Bennu impacting Earth between 2175 and 2199. Scientists closely monitor its trajectory for any changes caused by the effects of sunlight on its rough surface.
Ryugu is classified as a C-type asteroid with a slightly higher reflectivity than Bennu. It is about twice the diameter of Bennu with a similar top-like shape. It is also a rubble-pile asteroid and might have formed from the breakup of the same primitive parent asteroid as Bennu. Both asteroids have a rugged surface with large rocks and boulders.
Ryugu’s surface material is less water-rich than Bennu’s. Ryugu has undergone thermal alteration, perhaps relating to proximity to the impact that disrupted its parent body. Bennu, on the other hand, is thought to have remained relatively unchanged since it formed. Hayabusa2, which visited Ryugu, collected samples successfully returned to Earth in 2020.
Ryugu Analysis
Samples returned from the asteroid Ryugu are similar to Ivuna-type CI carbonaceous meteorites, according to Tetsuo Yokoyama and his colleagues in with JAXA.
Ryugu predominantly consists of phyllosilicate, serpentine and saponite, along with minerals like dolomite, breunnerite, pyrrhotite and magnetite. These minerals are products of precipitation from aqueous solutions. Inside Ryugu’s parent body, primary minerals would have transformed into these secondary minerals through aqueous alteration in solutions of melting ice – a phenomenon akin to that observed in CI chondrite meteorites. The intensity of aqueous alteration on Ryugu has been so significant that only a few primary minerals remain, mirroring the characteristics of CI chondrites.
Following the initial aqueous alteration, the Ryugu sample doesn’t seem to have undergone heating above 100-degrees Celsius until the present. However, a substantial portion of the interlayer water between phyllosilicate layers evaporated into space, distinguishing it from CI chondrites.
These meteorites originate from C-type asteroids, abundant in the solar system, making the Ryugu sample a primordial specimen that closely aligns with the average composition of the solar system. The chemical composition ratio of CI Ivuna-type chondrite meteorites is believed to mirror that of the entire solar system, establishing Ryugu as the most primitive celestial body that has retained the chemical composition of the entire solar system since its formation.
NASA and JAXA team’s analysis reports that Ryugu has a rich assortment of organic molecules. Abiotic chemical reactions in asteroids can make organic molecules that are some of life’s ingredients. Carbonaceofus chondrite meteorites have been found to contain protein building blocks, amino acids and DNA building blocks, purines and pyrimidines. An iron and lithium-containing protein of extraterrestrial origin has also been reported.
Ryugu contains many types of organics that form with liquid water, including carboxylic acids, polycyclic aromatic hydrocarbons, aliphatic amines and nitrogen-containing heterocyclic compounds.
“So far, the amino acid results from Ryugu are mostly consistent with what has been seen in certain types of carbon-rich meteorites that have been exposed to the most water in space,” said NASA’s Jason Dworkin.
“However, (purine and pyrimidine components of DNA and RNA) which have been discovered in some carbon-rich meteorites, have not yet been identified in samples returned from Ryugu,” said Daniel Glavin of NASA Goddard.
What will a full, detailed analysis of asteroid Bennu samples reveal?
Destination: Apophis
The OSIRIS REx mission has been extended as OSIRIS APEX. The main OSIRIS spacecraft used its return to Earth as a gravity assist on a new course toward asteroid Apophis. It fired its engines about 20 minutes after releasing the SRC samples, sending it on another long, looping voyage.
Apophis is approximately 1,214 feet in diameter in an orbit that crosses Earth’s orbit. Apophis is expected to make an extremely close approach to Earth on April 13, 2029. It will pass inside the orbits of communication satellites but is not anticipated to collide with Earth during this encounter. However, a small possibility of impact remains during a subsequent close approach in the year 2036.
On Oct. 13, 2023, a Falcon Heavy rocket launched with NASA’s Psyche mission, flying six years out to asteroid Psyche between the orbits of Mars and Jupiter. For the first time ever, an asteroid will be explored that is made, not of rock or ice, but of metal, about 140 miles in diameter!
Launched in 2021, NASA’s 12-year Lucy mission will explore more asteroids than any other spacecraft, flying by two asteroids in the main asteroid belt, and by eight Trojan asteroids that share an orbit with Jupiter.
Stay tuned for more astrogeology reports in the December EXPORER.