NMNH in Review: How an Asteroid Sample Traveled From Outer Space to the Museum’s Mineral Hall

After a 500 million mile journey, a piece of the asteroid Bennu is now on display at the Smithsonian. But how did it get here?

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The Smithsonian is the first institution to display a Bennu sample to the public; it is on exhibition in the meteorite gallery of the museum’s Janet Annenberg Hooker Hall of Geology, Gems, and Minerals. James Di Loreto and Phillip R. Lee, NMNH

2023 was a banner year for the National Museum of Natural History marked by the arrival of significant specimens, the unveiling of multiple exhibitions and hundreds of scientific publications. Tune in to the “NMNH in Review” series over the next month to learn about a new orca skeleton, historic asteroid samples and the top ten discoveries made by museum scientists this year. Read previous installments here.

Just over two decades ago, the asteroid Bennu was nothing but a distant light in the night sky, shining from 200 million miles away. In 1999, the ancient space boulder crept close enough to Earth to be observed by the Lincoln Near-Earth Asteroid Survey. It was an exciting discovery that enabled scientists to analyze Bennu through radar imaging, gathering data about its shape, size and composition from afar. But those scientists never could have imagined that 24 years later, NASA would reach out into the cosmos and bring a piece of Bennu back to Earth.

On September 24th, NASA’s OSIRIS-REx mission delivered dust and rocks collected from Bennu’s surface to Earth. This historic endeavor was the first asteroid retrieval to be launched by the United States, and its success was decades in the making. Now in the hands of Earth’s scientists, samples of the asteroid will undergo numerous tests – and potentially answer dozens of questions about Earth’s deep history and the origins of the Solar System. But one piece – a rock slightly larger than a pea – is reserved for public display at the Smithsonian’s National Museum of Natural History.

“The future is today,” said Tim McCoy, curator of meteorites at the museum and a collaborator on the OSIRIS-REx mission. “Six weeks after it landed on this planet, we put it on exhibit. That’s something I’ve waited 20 years for.”

A Deep Time Capsule

Although asteroids like Bennu are not of our planet, they can tell us a lot about how it formed and how life evolved on its surface. Earth formed about 4.5 billion years ago, but its oldest preserved rocks are only four billion years old. That’s because the Earth is really good at destroying rocks, explained McCoy. Plate tectonics, volcanism, weathering and other processes grind and degrade them over time. Thus, 500 million years of Earth’s history have been lost from its geologic record. Bennu, on the other hand, is made up of rocky matter that dates back to the very formation of our Solar System – spanning all 4.5 billion years of its existence.

The Bennu Asteroid photographed by the OSIRIS-REx spacecraft on December 2nd, 2018. NASA/Goddard/University of Arizona

Scientists think that within 10 million years of the birth of the Solar System, Bennu’s current composition was already established. It was chosen as the target for the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer) mission in part because of its proximity to Earth, but also because early observations of the asteroid suggested that it contained the essential ingredients for life: carbon and water. A large body of research suggests that meteorites from asteroids like Bennu were the vehicles that delivered these life-giving compounds to early Earth.

“Everything that we think of here on Earth – whether it’s the apple you have for lunch, your gold watch, the car you drive, or the tree that lives in your yard – came from the elements that were delivered to Earth either while it was forming, or later from asteroids and meteorites accumulating to make this planet,” McCoy says.

Acquiring a sample of Bennu would allow scientists like McCoy to analyze its composition down to nanometers, breaking particles of rock and dust apart to reveal their atomic structure, chemical makeup and mineralogy. In addition to carbon and water molecules, they’ll be looking for amino acids – the building blocks of proteins and thus, life.

Because the sample was excavated directly from Bennu and carried to Earth in a protective capsule, it has not been contaminated by Earth’s atmosphere. As a result, the Bennu sample offers a pristine look at the very minerals and compounds that may have jump-started life on Earth.

From Outer Space to Planet Earth

In September of 2016, the OSIRIS-REx unmanned spacecraft launched from Cape Canaveral, Florida and began its long journey to Bennu. This relatively small spacecraft is about the size of a 15-passenger van, and it is equipped with a 11-foot-long robotic arm called a Touch-And-Go Sample Acquisition Mechanism, or TAGSAM, which it used to reach out and retrieve sample material from Bennu’s rocky surface.

The journey from Earth to Bennu is not a straight shot. “You’re essentially chasing it around the sun,” McCoy says. Before OSIRIS-REx could enter Bennu’s orbit, it had to catch up with the asteroid as it traveled around the sun. Four days after the spacecraft departed Earth, OSIRIS-REx entered the sun’s gravitational field and circled it once. Then, about a month later, the spacecraft passed by Earth at a distance of about 10,700 miles, initiating a gravity-assist maneuver wherein Earth’s gravity tilted OSIRIS-REx’s orbit to match that of Bennu, sending it on course toward the asteroid.

Two years after its launch, in August of 2018, the OSIRIS-REx got its first glimpse of Bennu. The spacecraft snapped a grainy photo of the asteroid from 1.4 million miles away and sent it back to Earth. Just a few months later, in November, it delivered clearer images that showed the asteroid’s shape and some of its surface features. Bennu is slightly wider than the Empire State Building is tall, and it’s not perfectly round. It’s shaped more like a spinning top, with a wide diameter at its equator that narrows slightly at its poles. Its surface is extremely uneven and rocky with many hazardous boulders – a surprising discovery for the OSIRIS-REx research team, who did not expect to find such treacherous terrain.

The OSIRIS-REx spacecraft unfurled its robotic arm Oct. 20, 2020, and briefly touched the asteroid Bennu to collect dust and rock from its surface. NASA/Goddard/University of Arizona

When OSIRIS-REx finally arrived at Bennu on December 3rd, 2018, it became apparent that finding a safe sample-collection site would be challenging. The spacecraft orbited Bennu for over two years, mapping its surface and searching for the perfect site. Finally, the research team on Earth selected a 66-foot-wide northern crater that they named “Nightingale” for the sample collection. Evidence suggested that this crater was newly formed, and thus its regolith – the rocks and dust on its surface – would be freshly exposed and ripe for collection.

In October of 2020, OSIRIS-REx initiated its collection maneuver. In order to approach the Nightingale crater, the spacecraft first had to maneuver past a boulder the size of a two-story building, which the research team nicknamed “Mount Doom.” After a nail-biting 11-minute coast past this treacherous obstacle, OSIRIS-REx arrived at the Nightingale crater and began its slow descent towards Bennu’s surface. Once it kissed the ground, it outstretched its robotic arm and delivered a blast of nitrogen gas toward the ground to kick up regolith. OSIRIS-REx gathered the sample and stored it inside the spacecraft’s inner collection capsule.

Once the collection was complete, the spacecraft began slowly drifting away from Bennu. It soared just two miles above the surface as it took images of the asteroid one last time, capturing all 360 degrees of Bennu. Later, McCoy and colleague Erica Jawin, a research geologist formerly at NMNH but now at the Smithsonian Air and Space Museum, used the images taken by OSIRIS-REx to construct the first full geologic map of the asteroid. Finally, the spacecraft fired its thrusters and withdrew from Bennu, embarking on its two year, 500 million mile journey back to Earth.

After orbiting the sun twice, OSIRIS-REx reached Earth on September 24, 2023. Seven years of space flight led up to the most pivotal moment of the mission: when OSIRIS-REx would release the sample back to Earth. If all of its instruments did not deploy exactly as planned, the capsule could crash-land in the Utah desert – scattering the sample across the sand and contaminating it.

The sample return capsule from NASA’s OSIRIS-REx mission is seen shortly after touching down in the desert, Sept. 24, 2023, at the Department of Defense's Utah Test and Training Range. NASA/Keegan Barber

Aboard OSIRIS-REx, a severing system cut the cable that tethered the capsule to the spacecraft and a spring-like mechanism ejected it. But OSIRIS-REx did not follow the sample down to Earth. Instantly renamed OSIRIS-APEX, it fired its thrusters and set off on course for the asteroid Apophis, where it will orbit and collect images of its surface. The Bennu sample capsule hurtled toward Earth at more than 27,000 miles-per-hour before touching down safely in the Department of Defense's Utah Test and Training Range.

An Information Goldmine

At the NASA Johnson Space Center in Houston, Texas, curation experts spent ten days meticulously deconstructing the sample capsule to reveal the treasures inside. When they finally looked within, they were astonished to find it brimming with regolith. The goal of the mission was to collect at least 60 grams of asteroid material, enough to study for decades to come. But OSIRIS-REx had gone above and beyond, returning more than 70 grams of Bennu – more than enough to fill your average coffee cup.

Researchers work to open the lid of the capsule containing the asteroid samples collected by the OSIRIS REx spacecraft. Robert Markowitz

Thanks to the highly sophisticated instruments available today, scientists can glean massive amounts of information from tiny pieces of an asteroid sample. Using an scanning electron microscope, for example, mineralogists can determine an asteroid’s composition from a piece the size of a grain of rice, explained Cari Corrigan, a research geologist and the museum’s curator of Antarctic meteorites. “People can do analyses on tiny, tiny amounts of material. And that gets better over time,” she says. 75 percent of the Bennu samples will be reserved for research, enough for scientists to study long into the distant future.

The Bennu samples have been on Earth for only 12 weeks. Yet scientists are already extracting critical insights from it. Initial analyses confirmed that the asteroid does, in fact, contain carbon and water molecules. But this is just the beginning. Moving forward, a network of over 200 scientists from around the world will study the sample to understand exactly what it’s made of and how its components are assembled. “What we know now is a tiny piece of what we will know two years, five years, ten years from now,” McCoy said.“ The story is going to get a lot deeper.”

A smaller portion of the sample has been set aside for display. On November 3rd, the museum unveiled a piece of the Bennu sample to the public for the first time in the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals meteorite gallery. In addition to the sample, visitors can see scale-models of the OSIRIS-REx spacecraft and the Atlas V11 rocket that carried it, and a short film about the mission.

"Six weeks after it landed on this planet, we put it on exhibit. That’s something I’ve waited 20 years for.” — Tim McCoy, NMNH Curator of Meteorites

Although the sample on display may be small, “You look at it and it gives you chills,” said Michael Lawrence, the museum’s assistant director of exhibitions. He thinks that seeing it in person drives home the incredible feat accomplished by the OSIRIS-REx mission – traveling beyond the reaches of humanity to bring back an object that may tell us how life began on Earth. “I just find that astonishing,” Lawrence said.

McCoy and Corrigan hope that making this piece of Bennu available to the public will inspire the next generation of scientists and researchers. According to Corrigan, when young learners visit the museum and see a specimen from outer space, it piques their curiosity and invites them to ask questions – questions that could one day become the subject of a major study.

A sample of the asteroid Bennu is now on view at the Smithsonian’s National Museum of Natural History after being unveiled to museumgoers on Friday Nov. 3, 2023. James Di Loreto and Phillip R. Lee, NMNH

“This is the first time [the United States] has seen a sample return from the surface of a planetary body in 50 years,” McCoy says. He recalls being deeply inspired by the Apollo mission in the 1970s and considers himself a part of the Apollo generation. Now, OSIRIS-REx will usher us into a new age of scientific discovery – wherein we may finally begin to understand the origins of our existence.

“This is the OSIRIS-REx generation,” he says. “The Bennu generation.”

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