After a long, successful, and fascinating journey, NASA's OSIRIS-REx spacecraft is finally about to return its precious cargo to Earth.
On September 24, the mission will drop off its collection canister, before zipping back into space on another mission.
The cargo it will deliver consists of samples of dust and rubble from a carbon-rich asteroid named Bennu, which is thought to have formed very early in the history of the Solar System, and which has been drifting around relatively unchanged for the 4.5 billion years or so since.
In its collection canister, OSIRIS-REx is ferrying around 250 grams (8.8 ounces) of invaluable Bennu dirt. That canister will be dropped within a 59-kilometer by 15-kilometer ellipse (37-mile by 9-mile) inside a United States Department of Defense testing and training zone in the Utah desert.
NASA scientists estimate that the capsule will enter Earth's atmosphere at 14.41 UTC (10.41AM EDT), and touch down some 13 minutes later.
The cargo that will be dropped off is a big deal. It represents the biggest haul of asteroid rubble ever brought back to Earth – although it's only the third haul so far. Japan's collections from asteroids Itokawa and Ryugu arrived back in 2010 and 2020, respectively.
But Bennu is a particularly exciting asteroid. It's classified as a B-type, which means that it's thought to contain volatile elements in addition to its high carbon content. It's essentially a time capsule of the early Solar System that could help answer such questions as whether Earth's water and other ingredients for life were delivered by asteroids and meteors.
"There are two things pervasive on Earth: water and biology," says astrochemist Jason Dworkin, OSIRIS-REx project scientist at NASA Goddard. "Both can severely alter meteorites when they land on the ground and muddle the story told by the sample's chemistry and mineralogy. A pristine sample could provide insights into the development of the Solar System."
OSIRIS-REx's mission has been a careful one. The spacecraft launched from Earth in September 2016, and spent just over two years traveling to the asteroid, which has an orbit that brings it close to Earth every 6 years or so. In December 2018, OSIRIS-REx parked in orbit around Bennu, and spent the next two years observing the asteroid, and swooping in for sample collection.
It departed for its journey back to Earth in May 2021, and NASA scientists have been preparing for its return ever since. Once the capsule has been collected, it will immediately be taken to a portable clean room at the site to ensure minimal Earth contamination.
In addition, scientists will take samples of the ground and air around the capsule's landing site. This can be compared to the sample, once it has been opened and analyzed, to identify local contaminants. We won't know the results of the first analysis until 11 October, but that's not so long to wait. After all, these are big questions that scientists hope a cup of stardust will answer.
"This is all about understanding our origins," OSIRIS-REx principal investigator Dante Lauretta said back in 2020, "addressing some of the most fundamental questions that we ask ourselves as human beings: Where did we come from? And are we alone in the Universe?"
Oh, and philatelists take note: there's going to be a special commemorative postage stamp. Heckin' A.