NASA's Osiris-Rex probe carrying first asteroid sample returns to Earth

The climactic end of a seven-year voyage comes when a NASA capsule lands in the Utah desert, carrying to Earth the largest asteroid samples ever collected.

The Osiris-Rex probe's final, fiery descent through Earth's atmosphere will be perilous, but the US space agency has been hoping for a soft landing.

Scientists have high hopes for the sample, saying it will provide a better understanding of the formation of our solar system and how Earth became habitable.

Four years after its 2016 launch, the probe landed on the asteroid Bennu and collected roughly 250 grams of dust from its rocky surface.

Even that small amount, NASA says, should "help us better understand the types of asteroids that could threaten Earth" and cast light "on the earliest history of our solar system," NASA Administrator Bill Nelson said.

"This sample return is really historic," NASA scientist Amy Simon said. "This is going to be the biggest sample we've brought back since the Apollo moon rocks" were returned to Earth.

But the capsule's return requires "a dangerous maneuver," she acknowledged.

The return concludes

The fiery passage through the atmosphere came only in the last 13 minutes, as the capsule hurtled downward at a speed of more than 27,000 miles per hour, with temperatures of up to 2,760 Celsius.

Its rapid descent was supposed to be slowed by two successive parachutes as it made its way to the 37-mile by nine-mile landing zone.

The main chute, however, deployed "much higher than was originally anticipated," at about 6,100 meters rather than 5,000 feet, NASA said.

NASA images showed the tire-sized capsule on the ground in a desert wash, with scientists approaching the device and taking readings.

Eventually, they concluded the capsule was not breached, meaning its all-important air-tight seal remained intact, avoiding any contamination of the sample with desert sands.

The team then lifted the capsule by helicopter to a nearby "clean room."

Meanwhile, the probe that made the space journey fired its engines and shifted course away from Earth, NASA said, "on its way" for a date with another asteroid, known as Apophis.

Scientists predict that an asteroid will come within 20,000 miles of Earth in 2029.

Japanese samples

On Monday, the sample heads to the Johnson Space Center in Houston for additional study, and NASA plans to announce its first results at a news conference on October 11.

Most of the sample will be conserved for study by future generations. Roughly one-fourth will be immediately used in experiments, and a small amount will be sent to mission partners Japan and Canada.

Japan had earlier given NASA a few grains from asteroid Ryugu, after bringing 0.2 ounces of dust to Earth in 2020 during the Hayabusa-2 mission. Ten years before, it had brought back a microscopic quantity from another steroid.

But the sample from Bennu is much larger, allowing for significantly more testing, Simon said.

Earth's origin story

Osiris-Rex is set to release the capsule — from an altitude of more than 108,000 kilometres — some four hours before it lands.

The fiery passage through the atmosphere will come only in the last 13 minutes, as the capsule hurtles downward at a speed of more than 43,000 kilometres per hour, with temperatures of up to 2,760 Celsius.

Its rapid descent, monitored by army sensors, will be slowed by two successive parachutes. Should they fail to deploy correctly, a "hard landing" would follow.

If it appears that the target zone (37 by 9 miles) might be missed, NASA controllers could decide at the last moment not to release the capsule.

The probe would then keep its cargo and make another orbit of the sun. Scientists would have to wait until 2025 before trying a new landing.

If it succeeds, however, Osiris-Rex would head toward a date with another asteroid.

Asteroids are composed of the original materials of the solar system, dating to some 4.5 billion years ago, and have remained relatively intact.

They "can give us clues about how the solar system formed and evolved," said Osiris-Rex program executive Melissa Morris.