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Inside the bland, brick-and-steel Building 34 at the NASA Goddard Space Flight Center in suburban Maryland, scientists are about to run a series of tests that will have profound results. They are investigating about four grams of rocks and dirt scooped from the asteroid Bennu as part of the OSIRIS-REx mission, which returned a spacecraft to Earth last September with a tiny cargo—121.6 grams in total, or less than five ounces. Present at the creation of the solar system, when clouds of gas and dust were coalescing into the sun and the planets, the dirt awaiting analysis at the Goddard lab is among the oldest stuff on Earth. The spacecraft traveled 3.86 billion miles on a mission that took seven years in order to collect it.
The “O” in OSIRIS-REx stands for “Origins,” which in this case applies to the beginning of everything on Earth. “This is the feedstock of life, of oceans, of everything you know,” said Tim McCoy at the November 2023 unveiling of a miniscule piece of Bennu now on display at the Smithsonian’s National Museum of Natural History.
McCoy, curator of meteorites at the museum, is analyzing other samples of the asteroid in the museum’s Department of Mineral Sciences to classify and describe the textures of the rocks and the kinds of minerals they contain. The sample that has just arrived at Goddard’s Astrobiology Analytical Laboratory will offer different information. I’ve come to the lab on this stifling June day to watch how the scientists here will get at it.
Lab director Jason Dworkin and Danny Glavin, a senior scientist for NASA’s sample return missions, meet me just outside what’s known as a white room, which because of constant air filtering and limited personnel has air as free of dust and bacteria as a neonatal intensive-care unit. The room is furnished with benches topped by controlled cases made of clear plastic. We are separated from the white room by strips of heavy plastic, like those used in a butcher shop to divide cold storage from counter space. Through a window, I can see the small glass vial holding four grams of asteroid. For a moment, we all behold it, and I half expect it to glow from sheer rarity, but it’s very dark, almost black, and looks like ash. “It’s sticky,” says Glavin. “It has a sticky, clay-like consistency. That’s essentially what it is, like the clay we see on Earth.”
One thing scientists know from the data returned by the OSIRIS-REx spacecraft during its two-year orbit of Bennu is that at some point in the asteroid’s long history, it was wet. They also know that it is rich in carbon, the essential chemical constituent of all life on Earth. A team of analysts at the Carnegie Institution for Science reported that with a percentage of 4.7, the sample has the highest abundance of carbon of any extraterrestrial sample—meteorite or returned material—that the institution has ever measured. And that’s where the Astrobiology Analytical Laboratory comes in.
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The scientists here want to understand how asteroids like this one became part of the story of life on this planet. Astrobiologists believe that the nucleic acids RNA and DNA first developed with some level of contribution from amino acids and other molecules that rode in on asteroids like Bennu billions of years ago. To test that hypothesis, they will study the organic molecules in the Bennu sample.
“Most of my work in the last 20 years has been on meteorites,” says Dworkin. “These are remnants of the formation of planets, and so [they have] the raw materials that went into planets from a mixture of the interstellar medium and the protosolar nebula.” On Earth, those raw materials have been obscured by tectonic and other geologic activity, by the heat caused by a barrage of impacts that occurred in the first billion years of the planet’s history, and by the very life that, once started, proliferated and evolved, wiping out its own origin story. “There’s nowhere on Earth we’ve ever looked at that isn’t already inhabited,” says Dworkin.
But Bennu underwent none of those geologic or biologic processes; the word used most often by the scientists on the OSIRIS-REx mission team to describe the samples is “pristine.” To keep this one pristine, the lab follows careful protocols: People entering the white room where the sample resides don masks, hairnets, lab coats, shoe covers and nitrile gloves. A sticky mat at the white room door traps any loose particle from the shoe covers. The case holding the glass vial of sample is actually an airlock, with two hatches. Any tools or smaller objects that enter the white room where the sample is kept pass through one hatch, which is closed before the corresponding hatch on the other side is opened.
Glavin says that although they’re happy that they can now begin work, transporting the sample here and taking the responsibility for it in the lab is stressful. “You can do the math,” he says. “The mission cost [roughly] $1 billion, and we have 3.3 percent of the sample returned.” By that calculation, this half-vial of ashy regolith is worth $33 million, but to scientists studying the origins of life, it’s invaluable. Dworkin has received in his lab other invaluable samples, including dissolved extracts from the asteroid Ryugu, brought to Earth by a Japanese spacecraft in 2020. He has been preparing for the Bennu samples for 20 years—he joined the project in 2004, 12 years before the probe was launched—and is one of 233 scientists around the world representing 38 scientific institutions who will spend the next 15 months unlocking what they all hope will be the full biography of Bennu. All 38 institutions will divide up only about 25 percent of the 121.6 grams of asteroid returned.
“We interpret the organics in the context of mineralogy,” says Glavin. “We don’t work in isolation. One set of experiments can’t tell the whole story.” The OSIRIS-REx science team published an introduction to that context late last month in the science journal Meteoritics & Planetary Science. The mineralogists identified magnesium-sodium phosphates among the asteroid’s constituents, phosphate salts that can be dissolved in water and that can therefore participate in chemistry. It was an unexpected finding, because the OSIRIS-REx sensors didn’t detect the phosphates while the spacecraft was mapping Bennu.
“This is why sample return is so important,” says Glavin. Remote sensing cannot give a complete accounting of a celestial body’s composition.
Phosphates are among the constituents of nucleotides, which in turn form the structural units of nucleic acids, like DNA. Finding the phosphates in the returned sample, says Dworkin, “permit[s] us to ask the question if these soluble phosphate salts could have contributed to the formation of phosphorylated organic compounds.”
“We have not done any testing for these yet,” he adds.
One finding, mentioned in the paper almost in passing, gives me goosebumps. Lindsay Keller, who manages the Electron Beam Analysis Labs at the NASA Johnson Space Center, discovered grains thought to have originated in red giant stars—stars that are older than the sun. Also found were traces of supernova ejecta, the chemicals blasted outward in the fatal explosion of a star.
Behind us, a door opens, and a young man announces that he’s about to start the test. Angel Mojarro is a postdoctoral researcher who started at Goddard last February. “My first job out of grad school is analyzing Bennu,” he says, with a smile that shows he considers himself incredibly lucky.
In a room where various types of mass spectrometers and other large instruments share space with computer monitors, Mojarro is holding another capped glass vial in his gloved hands. In it, a tiny sphere the color of a poppy seed and about three times that size clings to the glass. (This particle barely makes a dent in the four-gram sample meted out to the lab for processing; plenty of sample remains.) Mojarro extracts it with long metal tweezers and places it in a receptacle in a gas chromatography mass spectrometer, which loosely resembles an office printer, then closes a door. For the few seconds between its removal from the vial and placement in the mass spectrometer, the Bennu particle is exposed to air, but given the test Mojarro is about to perform, Dworkin says exposure to air is inconsequential.
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The mass spectrometer first vaporizes the particle by delivering a thermal shock, then propels the resulting gas through coils of glass capillaries. The spectrometer measures the mass of the individual molecules and generates a spectrum, indicating the chemical composition of the gas. In 90 minutes, Mojarro will have the result: a fingerprint of the soluble and insoluble organic compounds in the asteroid sample. That information cannot be reported until the paper on this particular study is published later this year, after it has been peer-reviewed.
An earlier similar test found the presence of multiple different amino acids, organic molecules that can combine to form proteins. Most of them were glycine, the simplest in structure of all the amino acids.
In addition to working with meteorites and asteroids, the Astrobiology Analytical Laboratory studied samples of Comet Wild 2 (pronounced “VILT-two”) returned in 2006 by NASA’s Stardust spacecraft. In 2008, Glavin and Dworkin isolated glycine from minute grains of the comet’s tail. The next step was to prove that the glycine came from the comet, not from operations on Earth before the spacecraft was launched. To confirm its extraterrestrial provenance, they and their colleagues subjected the microscopic amount of Wild 2 to isotopic analysis that confirmed it came from space. It was the first observation of an amino acid from a comet. The discovery strengthened the hypothesis that the carbon-based compounds required for life on Earth came at least in part as hitchhikers on the asteroids and comets that bombarded the planet in its babyhood.
As scientists around the world conduct research on the Bennu samples, asteroids are having a moment. The OSIRIS-REx spacecraft is continuing its mission, now to the asteroid Apophis, and two other NASA probes are also on their way to other asteroids. Dworkin says that his favorite part of the OSIRIS-REx mission is what will happen to the remaining 75 percent of the sample after it has been divided: “The rest goes to the future,” he says. To future scientists who will have better instruments for studying such material, who will know more about asteroids than today’s scientists do, and, Dworkin says, “who will ask questions we haven’t thought of.”