Just a few miles from the glamor of the famous French Riviera lies a little-known French national laboratory that is largely used to conduct material analysis for next-generation semiconductors. But a team at the Valbonne lab, the CNRS-CRHEA (Research Center for Hetero-Epitaxy and its Applications) is now analyzing 100 milligrams of tiny grains from NASA’s OSIRIS-REx sample return mission to asteroid Bennu.
In fact, the Valbonne sample contains a few surprises that will be announced by NASA as early as next week, Guy Libourel, a cosmochemist at the Observatoire de la Cote D’Azur in Nice and co-principal investigator of OSIRIS-REx, told me here. . This object is very pristine because since it was formed, it has not evolved, it has not transformed, he says.
The sample, safely encased in nitrogen since its retrieval by OSIRIS-REx, dates from the earliest beginnings of our solar system’s protosolar nebula, about 4.567 billion years ago.
The French team used a technique known as hetero-epitaxy to analyze various crystalline substrates to identify their mineralogy. Among other things, so far they have identified iron oxide, many sulfides. the elements of manganese and magnesium, as well as silicate serpentines that indicate the fact that Bennu was once filled with water.
Some of the mineral fragments inside Bennu could be older than the solar system itself, NASA says.
These tiny dust grains could be the same ones that were ejected from dying stars and eventually coalesced to make the sun and its planets nearly 4.6 billion years ago, NASA notes.
What makes the French laboratory in Valbonne unique is that it uses a newly improvised cathodoluminescence method. This is a process by which beams of electrons inside a scanning electron microscope strike luminescent materials and create either an image or a spectrum, Marc Portail, a French CNRS researcher, told me in the lab.
Much of the material in the Bennu sample consists of silicate crystals capable of emitting light when bombarded with a high-frequency electron beam. By analyzing the luminescence from both the images and the spectra as the beams strike the sample, researchers learn details about the crystalline distribution of the sample’s minerals.
In short, the scanning electron microscope allows us to have a very detailed map of these tiny grains to analyze the mineralogy in detail, says Libourel.
What’s so special about these Bennu samples?
Meteorites that survive our planet’s violent, fiery surface become contaminated when they land on dirt, sand or snow, nasa says. Some are even battered by the elements, like rain and snow, for hundreds or thousands of years. Such events change the meteorites’ chemistry, obscuring their ancient records, NASA notes.
But the samples inside the spacecraft that landed in the Utah desert last September were fully protected from the ravages of crossing Earth’s atmosphere from the start. Unlike meteorites, NASA’s samples were carefully encased in chemically inert nitrogen to prevent oxygen from damaging our own atmosphere.
NASA chose Bennu as its target because it is rich in carbon and could contain the chemical building blocks of life as we know it. The asteroid also has a small chance of hitting Earth early next century. If so, Nasa says studying Bennu could also help us learn how to be prepared to defend ourselves against such a potential impact.
It’s pretty obvious that Bennu was part of a larger body at one point, so what we’re observing now is a piece of large boulders, Libourel says.
But the Bennu samples may arguably be more useful as long-term chemical mileposts for future planetary scientists.
The composition and mineralogy of asteroids observed from Earth (using telescopes) is assessed only by their optical spectrum, which measures the sunlight they reflect, Libourel says.
Being able to analyze the composition and mineralogy of Bennu in detail is a unique opportunity to learn the chemical ground truth for such a celestial object. Therefore, Bennu will forever remain a reference, says Libourel.
And here in Valbonne, we will have the sample by the end of next year, says Libourel.
What excites Libourel most about samples?
During my career as a cosmochemist, I have often analyzed meteorites, says Libourel. But these samples, he says, are preserved in nitrogen which enables us to analyze their primitive nature as if we were some 300 million kilometers away on Bennu.