OSIRIS-REx Mission: Insights from Bennu Asteroid Samples

 On a Sunday afternoon, precisely at 5 p.m. Italian time on September 24, 2023, a spacecraft capsule resembling a flying saucer made a gentle landing in the western Utah desert, USA. The capsule, which had separated from the OSIRIS-REx spacecraft, bore samples from the asteroid Bennu.

This marked the completion of NASA's maiden mission of returning asteroid fragments to Earth - a seven-year journey in space. These fragments, essentially space dust, hold potential insights into the solar system's history and life's origin on Earth. It's fair to say that the most intriguing part of this mission begins now.

One theory about life's inception on our planet suggests that the foundational elements, water and organic molecules, were transported here by asteroids. Studying objects like Bennu could provide support or contradict this theory.

ANTI-CONTAMINATION MANEUVER

To ensure the samples remained uncontaminated, the sealed capsule was promptly airlifted to a NASA "clean room," an uncontaminated lab with pristine air quality. Here, the capsule was exposed to a steady flow of nitrogen, a gas known for its non-reactive nature, to keep terrestrial contaminants at bay before the capsule was opened. For added safety, air, soil, and water samples were collected from the landing site to identify any terrestrial microorganisms outside the capsule.

Unlike meteorites, the 250 grams of rock and dust retrieved from Bennu remained unchanged after passing through Earth's atmosphere. This will enable scientists to study the asteroid's chemical and geological features — a carbon-rich collection of debris spanning 500 meters. They will also be able to examine the celestial body where Bennu originated 4.56 billion years ago, around the time the solar system was forming.

Next steps

In the upcoming days, the capsule will be transferred to NASA's Johnson Space Center in Houston. There, in specially designed nitrogen-filled containers, the capsule will be cautiously opened. The initial analysis will identify the types, color, weight, shape, volume, and porosity of the collected rocks. The filled-to-capacity container will also allow for the analysis of excess dust, giving a glimpse into Bennu's composition within a week.

Future generations of scientists will benefit from 70% of the rocks preserved by NASA, who will likely have access to more advanced scientific equipment. NASA will distribute 4-5% of the collected samples to mission partners in Canada and Japan while retaining the remaining 25% for thorough analysis by over 200 scientists across four continents.

BUILDING BLOCKS OF LIFE. 

We know that organic molecules containing carbon (an essential ingredient for life as we know it) cover nearly the entire surface of Bennu, but scientists studying Bennu must go one step further. As explained in Science, only 12 of the 20 amino acids that make up the millions of proteins essential to life have been identified on meteorites that have fallen to our planet, perhaps in part because the extraction methods used so far can destroy some of these molecules. Scientists on the OSIRIS-REx mission will rely on a less destructive technique that could capture all 20. 

Special attention will be paid to the amount of sinistral amino acids. Amino acids are molecules that can form in two mirror-like ways, left or right, but it has been found that proteins needed by living things prefer the former of the two configurations. The team will also search Bennu's dust for traces of more complex organic molecules, such as peptides (short protein segments) and sugars.

HUNTING FOR WATER

Another question to be answered is whether Bennu is actually as water-rich as telescopic observations suggest. These results indicate that 10 percent of the asteroid's mass is water encased in clay, and the asteroid also has long grains of carbonate, a mineral that precipitates from aqueous solutions. This suggests that liquid water was present not so much on Bennu, which is too small to have hosted it, but on the body from which it came, probably a larger asteroid.

WATER EVERYWHERE? Since Ryugu, the asteroid whose crumbs were reported by the Hayabusa2 spacecraft in 2020, also appeared to be altered by water, there is a possibility that this - and not the composition of the meteorites analyzed so far - is the standard composition in the Solar System. To survive re-entry through the Earth's atmosphere, meteorites must be dense and durable, not brittle like Bennu and Ryugu. This may have influenced our previous knowledge.