The rock was chosen as a target because of the things we think we know about it. Bennu is probably a remnant from the long-gone days of our solar system's formation, dated at around 4.5 billion years.
Its age makes it a prime candidate for study for people looking to better understand how Sol got to be, and learn details about potentially hazardous asteroids. It may also prove an invaluable clue as to how life here on Earth came to be.
Because of the above, Bennu was selected as the target for the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission, which left for it in 2016. The ship reached the asteroid in 2018, and spent the following three years sampling its surface.
In 2021 the spacecraft began its long journey home (in all, it covered a distance of 3.9 billion miles/6.3 billion km), and all of that ended on September 24, 2023, in the Utah desert, with a soft landing of a capsule containing the few precious 8.8 ounces (250 grams) of alien soil.
The landing part of the mission went without a hitch, with the capsule reaching our planet's surface as planned in the target area at the Utah Test and Training Range. It then took crews just one and a half hours to locate, load into a helicopter and transport the capsule to a temporary clean room located in a hangar on the premises.
The sample of alien rock is still there at the time of writing, being flooded inside the container that holds it with nitrogen. The gas is one of the few that we know of not to interact with chemicals, and shooting it at the sample will ensure contaminants originating here on our planet don't get in and spoil years of hard work and billions spent.
On Monday, September 25, the Bennu sample will be moved to the Johnson Space Center in Houston, where it will be removed from its canister. Science to be performed on it will begin with weighing and will continue intensively all over the world, as the sample will be split up and distributed to scientists.
The spacecraft that brought the sample home has now been renamed OSIRIS-APEX and is already en route to its next survey target, asteroid Apophis. As for Bennu, the piece of floating danger will continue to orbit our Sun just like we do, occasionally coming uncomfortably close to Earth.
According to the most recent study on its trajectory, published in 2021, Bennu has a cumulative 1-in-1,750 chance of impacting our planet between the years 2175 and 2199.
After a journey of nearly 3.9 billion miles, the #OSIRISREx asteroid sample return capsule is back on Earth. Teams perform the initial safety assessment—the first persons to come into contact with this hardware since it was on the other side of the solar system. pic.twitter.com/KVDWiovago— NASA (@NASA) September 24, 2023