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Victoria Thiem, Lockheed Martin System Safety Engineer conducts a rehearsal of NASA's first major asteroid sample recovery for its OSIRIS-REx mission, in Littleton, Colo. on June 27, 2023. OSIRIS-REx is the first U.S. mission to capture a sample from the surface of an asteroid and will arrive back on earth on Sept. 24.JASON CONNOLLY/AFP/Getty Images

Scientists in the United States and Canada are making final preparations for the arrival of a space capsule bearing precious cargo: fragments of rock and dust snatched from the surface of an asteroid that could shed light on the formation of Earth as a life-supporting planet.

The unmanned capsule is part of OSIRIS-REx, a NASA mission that launched in 2016 and collected a sample from the asteroid Bennu four years later. Its return journey is set to reach a dramatic conclusion on Sept. 24 when it enters Earth’s atmosphere high above western North America.

If all goes well, the cone-shaped craft, which is roughly the diameter of a car tire, will automatically deploy a parachute and touch down in the Utah desert at a military facility about 140 kilometres southwest of Salt Lake City. From there, the capsule will be whisked by helicopter to a temporary clean room and then to the Johnson Space Center in Houston.

“We’re very excited to be in the final phase of this long journey,” said Rich Burns, the mission’s project manager, at a news briefing at the Utah Test and Training Range on Wednesday.

The briefing followed a successful dress rehearsal of the retrieval process, using a mock capsule released from an altitude of about 2,130 metres.

Mission scientists estimate the OSIRIS-REx spacecraft was able to collect about 250 grams of material when it approached and briefly made contact with Bennu on Oct. 20, 2020.

The Canadian Space Agency is a participant in the mission and provided a laser altimeter that was used as part of the effort to map the 525-metre-wide asteroid and identify a favourable spot for the touch-and-go manoeuvre to capture a sample. In return, Canada is slated to receive a 4-per-cent share of the sample once it has been safely retrieved.

The mission marks the first attempt by the U.S. space agency to collect material from an asteroid, one of the solar system’s building blocks. It will also provide Canada with its first sample from any celestial body.

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A training model of the sample return capsule is seen is seen during a drop test in preparation for the retrieval of the sample return capsule from NASA's OSIRIS-REx mission on Aug. 30.NASA/Keegan Barber/Handout

“The great thing about a sample-return mission is that it’s a gift that keeps on giving,” Timothy Haltigin, senior mission scientist for planetary exploration at the Canadian Space Agency, told The Globe and Mail.

“It’s not just the science that we’re going to do on the samples in the next few months,” he said. “It’s being able to make those samples available to generations of Canadian researchers,” he said.

Images from OSIRIS-REx show Bennu to be a boulder-strewn heap of rubble barely held together by gravity, like a “droplet of rock,” according to Dante Lauretta, a planetary scientist at the University of Arizona and the mission’s principal investigator.

The carbon-rich asteroid is thought to be a repository of material that is representative of what Earth and its neighbouring planets were built from when the solar system formed more than 4.5 billion years ago.

A key goal for the mission is to preserve any volatile substances such as water and organic molecules that the Bennu sample may contain. These are typically lost when asteroid fragments fall to Earth as meteorites. A pristine sample from Bennu would potentially offer scientists their best window yet on the contents of the early solar system and their role in the emergence of life on Earth.

“We’re looking for clues as to why Earth is a habitable world – this rare jewel in outer space that has oceans, that has a protective atmosphere,“ Dr. Lauretta said during Wednesday’s briefing. “And of course, the biggest question, the one that drives my scientific investigations, is the origin of life.”

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