NASA's recovered Bennu asteroid samples show evidence of carbon, water

Rocks and soil collected from the asteroid Bennu and brought back to Earth last month by NASA's OSIRIS-REx probe are rich in carbon and contain water-bearing clay minerals that date back to the birth of the solar system, scientists said Wednesday. The discovery gives critical insight into the formation of our planet and supports theories about how water may have arrived on Earth in the distant past.

The clay minerals "have water locked inside their crystal structure," said Dante Lauretta, a planetary scientist at the University of Arizona and the principal investigator of the asteroid sample return mission, while revealing initial photographs of the material.

"And I want to stop and think about what that means," said Lauretta. "That is how we think water got to the Earth."

Rocky fragments and soil from the asteroid Bennu, returned to Earth last month by NASA's OSIRIS-REx probe, show the dark colors expected of carbon rich material. Samples revealed by NASA Wednesday were found just outside the main sample container, giving scientist an unexpected bonus. The main container, believed to hold about 8.8 ounces of rocks and soil, has not yet been opened. / Credit: NASA TV

"The reason that Earth is a habitable world, that we have oceans and lakes and rivers and rain, is because these clay minerals like the ones we're seeing from Bennu, landed on Earth four-and-a-half billion years ago, making our world habitable," said Lauretta.
"So we're seeing the way water got incorporated ... ultimately into planets."

The OSIRIS-REx sample return capsule landed in Utah Sept. 24, nearly three years after the spacecraft briefly pushed its innovative touch-and-go sample acquisition mechanism, or TAGSAM, into the the asteroid Bennu's rubble-strewn surface.

Researchers originally expected to have the TAGSAM open by now, revealing the half-pound or so of material estimated to be trapped inside. But they were surprised to find dust and small fragments from Bennu strewn about the interior of the sample return capsule, just outside the TAGSAM.

Opening TAGSAM was put on hold while scientists eagerly examined the unexpected bonus material — which turned out to provide a tantalizing glimpse of discoveries to come.

"It's been going slow, meticulous, but the science is already starting," said Lauretta, a planetary scientist at the University of Arizona. "This is scientific treasure."

The samples are being studied inside an environmentally isolated laboratory at the Texas space center where Apollo moon samples also are protectively housed. Initial examination of the asteroid dust by a powerful electron microscope revealed water-bearing clay minerals, sulfides and high concentrations of carbon.

Along with carbon compounds and clays, sulfides are "a critical element for planetary evolution," said Lauretta. "It determines how quickly things melt, and it's also critical for biology. A lot of the amino acids that give structure to our proteins use sulfur to link and provide those bridges."

Researchers at the Johnson Space Center use a
Researchers at the Johnson Space Center use a

NASA Administrator Bill Nelson said the captured Bennu samples represent "the biggest carbon-rich asteroid sample ever returned to Earth."

"The carbon and water molecules are exactly the kinds of material that we wanted to find," he said. "They are crucial elements in the formation of our own planet, and they're going to help us determine the origin of elements that could have led to life."

Once TAGSAM is opened and the entire sample is categorized, about 25% will be reserved for study by the OSIRIS-REx team at the Johnson Space Center. Another 4% will be shared with the Canadian Space Agency, which supplied the OSIRIS-REx laser altimeter instrument, and about 0.5% will be given to the Japan Aerospace Exploration Agency.

A small portion of the material will be protectively stockpiled at a facility in White Sands, New Mexico, and the rest will be curated for eventual analysis by scientists around the world.

The samples revealed Wednesday are "the material that leaked out of the TAGSAM when we flipped it over," Lauretta said. "Underneath that flap, there's a whole treasure chest of material. And trust me, the sample science team can't wait to get their hands on it."

Equipped with three cameras, two spectrometers, a laser altimeter and an X-ray imaging system developed by college students, the OSIRIS-REx spacecraft and sample return capsule were launched atop a United Launch Alliance Atlas 5 rocket from Cape Canaveral on Sept. 8, 2016.

The spacecraft reached Bennu in December 2018, slipping into orbit around the 1,500-foot-wide asteroid for months of mapping and analysis. Nearly two years later, on Oct. 20, 2020. the spacecraft moved in and rammed the TAGSAM into the surface.

The collector, shaped like an inverted pie pan, fired a jet of nitrogen gas to stir up the soil beneath it at the moment of contact. As the gas exited through vents, small rocks and soil particles were captured in filters.

The asteroid Bennu, as imaged by NASA's OSIRIS-REx spacecraft. / Credit: NASA
The asteroid Bennu, as imaged by NASA's OSIRIS-REx spacecraft. / Credit: NASA

After backing away, OSIRIS-REx's robot arm deposited the capture device in an aerodynamic sample return container that was finally returned to Earth last month. The sample container then was flown from Utah to the Astromaterials Acquisition and Curation Office at the Johnson Space Center for two years of detailed analysis.

A key element of the OSIRIS-REx mission — the acronym stands for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer — is to learn more about the materials present at the birth of the solar system 4.5 billion years ago and how they came together to form the sun and its retinue of planets.

The composition and evolution of asteroids and comets is central to understanding where the water in Earth's oceans originated and even how life managed to arise from organic compounds and other chemicals transported to Earth.

A more down-to-Earth reason to study asteroids and comets is the risk of potential Earth impacts like the Tunguska event of 1908, when a body measuring 200 to 620 feet across exploded in the atmosphere over western Russia, flattening trees across 770 square miles.

One of the goals of the OSIRIS-REx mission is to understand the composition and structure of Bennu to get a better idea of what might work best to deflect a similar body on a collision course with Earth.

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