THE climactic end of a seven-year voyage is due today when a Nasa capsule lands in the Utah desert, carrying to Earth the largest asteroid samples ever collected.

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

The Osiris-Rex probe’s final, fiery descent through Earth’s atmosphere would be perilous, but the United States space agency was hoping for a soft landing around 9am local (1500 GMT), in a military test range in northwestern Utah.

Four years after its 2016 launch, the probe landed on the asteroid Bennu and collected roughly nine ounces (250g) of dust from its rocky surface.

Even that small amount should “help us better understand the types of asteroids that could threaten Earth” and cast light “on the earliest history of our solar system”, said Nasa administrator Bill Nelson.

“This sample return is really historic,” Nasa scientist Amy Simon told AFP. “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 would require “a dangerous manoeuvre”, she said.

Osiris-Rex was set to release the capsule – from an altitude of more than 67,000 miles (108,000km) – some four hours before it lands.

The fiery passage through the atmosphere would come 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 5,000ºF (2,760ºC).

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

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

Japanese samples

Once the tyre-sized capsule has touched down in Utah, a team in protective masks and gloves would place it in a net to be airlifted by helicopter to a temporary “clean room” nearby.

Nasa wanted this done as quickly and carefully as possible to avoid any contamination of the sample with desert sands, skewing test results.

Tomorrow, assuming all goes well, the sample will be flown by plane to Nasa’s Johnson Space Center in Houston, Texas. There, the box will be opened in another “clean room” – the beginning of a days-long process.

Nasa planned to announce its first results at a news conference on October 11.

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

Japan had earlier given Nasa a few grains from the 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 asteroid.

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

Earth’s origin story

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 programme executive Melissa Morris.

“It’s our own origin story.”

By striking Earth’s surface, “we do believe asteroids and comets delivered organic material, potentially water, that helped life flourish here on Earth,” said Simon.

Scientists believed Bennu, which was 1,640 feet (499.8m) in diameter, was rich in carbon – a building block of life on Earth – and contained water molecules locked in minerals.

Bennu had surprised scientists in 2020 when the probe, during the few seconds of contact with the asteroid’s surface, had sunk into the soil, revealing an unexpectedly low density, sort of like a children’s pool filled with plastic balls.

Understanding its composition could come in handy in the distant future, for there was a slight chance (one in 2,700) that Bennu could collide catastrophically with Earth, though not until 2182.

But Nasa last year succeeded in deviating the course of an asteroid by crashing a probe into it in a test, and it might at some point need to repeat that exercise – but with much higher stakes. – AFP, September 24, 2023.