NASA’s first asteroid samples fetched from deep space parachuted into the Utah desert on Sunday, capping off a seven-year journey.

In a flyby of earth, the Osiris-Rex spacecraft released the sample capsule from 100,000 kilometres out. The small capsule landed four hours later on a remote expanse of military land, as the mothership set off after another asteroid.

Scientists estimate the capsule holds at least a cup (or about 235ml) of rubble from the carbon-rich asteroid known as Bennu – but won’t know for sure until the container is opened.

Some of the rubble is said to have spilled and floated away when the spacecraft scooped up too much of it, with rocks jamming the container’s lid during collection three years ago.

Japan, the only other country to bring back asteroid samples, gathered about a teaspoon in a pair of asteroid missions in comparison.

The pebbles and dust delivered on Sunday represent the biggest haul to date from beyond the moon. Thought to be preserved building blocks from the dawn of the solar system 4.5 billion years ago, the samples will help scientists better understand how earth and life on it was able to form.

Osiris-Rex, the mothership, rocketed away on the $1 billion (€937m) mission in 2016. It reached Bennu two years later and, using a long stick vacuum, grabbed rubble from the small, roundish space rock in 2020. By the time it returned, the spacecraft had logged a staggering 6.2 billion kilometres.

NASA’s recovery effort in Utah included helicopters as well as a temporary clean room set up at the Defence Department’s Utah Test and Training Range.

The samples will be flown on Monday morning to a new lab at NASA’s Johnson Space Center in Houston. The building already houses the hundreds of kilograms of moon rocks gathered by the Apollo astronauts more than half a century ago.

The mission’s lead scientist, Dante Lauretta from the University of Arizona, will accompany the samples to Texas. The opening of the container in Houston in the next day or two will be “the real moment of truth,” given the uncertainty over the amount inside, he said ahead of the landing.

Engineers estimate the canister holds 250 grams of material from Bennu, plus or minus 100 grams. Even at the low end, it will easily surpass the minimum requirement of the mission, Lauretta confirmed.

It’s likely to take a few weeks to get a precise measurement, NASA says, but they plan a public show-and-tell in October.

Currently orbiting the sun 81 million kilometres from earth, Bennu is about one-half of a kilometre across, roughly the size of the Empire State Building – but shaped like a spinning top. It’s believed to be the broken fragment of a much larger asteroid.

During a two-year survey, Osiris-Rex found Bennu to be a chunky rubble pile full of boulders and craters.

The surface was so loose that the spacecraft’s vacuum arm sank about 0.5 metres into the asteroid, sucking up more material than anticipated – hence the jamming of the lid.

These close-up observations may come in handy late in the next century. Bennu is expected to come dangerously close to earth in the year 2182 – possibly close enough to hit.

The data gleaned by Osiris-Rex will help with any asteroid-deflection effort, according to Dante Lauretta

Osiris-Rex is already chasing after the asteroid Apophis – and is set to reach it in 2029.

This was NASA’s third sample return from a deep-space robotic mission. The Genesis spacecraft dropped off bits of solar wind in 2004, but the samples were compromised when the parachute failed and the capsule slammed into the ground. The Stardust spacecraft successfully delivered comet dust in 2006.

NASA’s plans to return samples from Mars are on hold after an independent review board criticised the cost and complexity. The Martian rover Perseverance has spent the past two years collecting core samples for eventual transport to earth.