A NASA capsule has landed in the Utah desert after a seven-year voyage, carrying to Earth the largest asteroid samples ever collected.
"Touchdown of the Osiris-Rex sample return capsule. A journey of a billion miles to asteroid Bennu and back has come to an end," a commentator said on NASA's live video webcast of the landing.
NASA chief Bill Nelson hailed the mission and said the asteroid dust "will give scientists an extraordinary glimpse into the beginnings of our solar system."
Four years after the Osiris-Rex probe's 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.
Osiris-Rex released the capsule - from an altitude of more than 108,000km - some four hours before it landed.
The fiery passage through the atmosphere came only in the last 13 minutes, as the capsule hurtled downward at a speed of more than 43,000km/h, with temperatures of up to 2,760C.
Once the tyre-sized capsule touched down in Utah, a team in protective masks and gloves were due to place it in a net to be airlifted by helicopter to a temporary "clean room" nearby.
NASA wants this done as quickly and carefully as possible to avoid any contamination of the sample with desert sands, skewing test results.
Stu Wylie of the US Air Force and Vicky Thiem of Lockheed Martin were first to approach the capsule after it reached Earth. They conducted a safety survey of the surrounding area before reporting back that the sample had not been breached.
Tomorrow, it 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 plans to announce its first results at a news conference on 11 October.
Most of the sample will be conserved for study by future generations.
Roughly a quarter of it will be immediately used in experiments, and a small amount will be 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 ounce 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 is much larger, allowing for significantly more testing, Ms 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 program 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," Ms Simon said.
Scientists believe Bennu, which is 499m in diameter, is rich in carbon - a building block of life on Earth - and contains 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 is a slight, but non-zero, chance (one in 2,700) that Bennu could collide catastrophically with Earth, though not until 2182.
But last year NASA 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.