A NASA spacecraft just landed on an asteroid to suck up rocky dust to bring back to Earth. Here's how the mission works.

• NASA's Osiris-Rex spacecraft landed on an asteroid called Bennu and collected samples of its rock on Tuesday.
• The probe, which is the size of a 15-passenger van, maneuvered around hazardous boulder fields to reach its small landing zone.
• NASA does not yet know whether Osiris-Rex scooped up enough rock. If it did, the sample could help scientists learn how life arose on Earth.
• The mission could also help NASA deflect the asteroid if it is found to be at risk of crashing into Earth.

NASA just landed a spacecraft on an asteroid.

If everything went as planned, the probe also sucked up a sample of dust and rock from the surface.

From 200 million miles away, NASA and its engineering partner, Lockheed Martin, instructed the Osiris-Rex spacecraft to descend to the surface of a space rock called Bennu, touching it for just five to 10 seconds on Tuesday evening. In that time, the probe should have collected samples from the asteroid's surface, though NASA won't confirm success in that maneuver for several more days. It's set to bring these pieces of Bennu back to Earth in 2023.

The spacecraft's name is short for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer. It beamed back confirmation that it had landed on Bennu's surface, and the signal reached Earth at 6:11 p.m. ET — about 18 minutes after the actual touchdown.Mission Control erupted in cheers and applause.

"Transcendental. I can't believe we actually pulled this off," Dante Lauretta, the mission's principal investigator, said during NASA's live broadcast of the operation. "The spacecraft did everything it was supposed to do."

The goal was for Osiris-Rex to pick up at least one 2.1-ounce (60-gram) sample, which is about a small bag of potato chips' worth of mass.It will take a few days to determine whether the probe did indeed snatch up enough rock.

The spacecraft has been orbiting Bennu since December 2018. It's set to leave in March 2021, samples in tow, then reach Earth on September 24, 2023.

The mission's research could be crucial over the next 100-plus years, since Bennu's path puts it at risk of crashing into Earth.

"Bennu is one of the most potentially hazardous asteroids, with a non-negligible chance of impacting the Earth at some point in the 22nd century," Lauretta said in September. "Part of our science investigation is about understanding its orbital trajectory, refining the impact probability, and documenting its physical and chemical properties so that future generations can develop an impact-mitigation mission, if that's necessary."

There are other important reasons to study Bennu as well: As new missions go deeper into space, they will need to make pit stops to mine asteroids for resources like water, which can be split into oxygen and hydrogen for rocket fuel. The data NASA is gathering from Bennu could help inform future asteroid-mining attempts.

Osiris-Rex is also, in a sense, a soul-searching mission. Asteroids are bits of ancient rock from the beginnings of the solar system 4.5 billion years ago. The leftover material that made the rocky planets — Mercury, Venus, Earth, and Mars — coalesced over time into asteroids, where it's largely preserved in its original form.

Some theories posit that asteroids delivered key ingredients for life to ancient Earth. On Bennu, scientists may find signs of those ingredients, cluing them in to how life arose on Earth (and possibly on Mars or Venus too).

If successful, this mission will be one of the first to return samples of primordial rock. Japan's Hayabusa-2 spacecraft is also set to bring back asteroid samples in December.

"This is all about understanding our origins, addressing some of the most fundamental questions that we ask ourselves as human beings: Where did we come from? And are we alone in the universe?" Lauretta said.

NASA's spacecraft dropped 3,000 feet to blast asteroid dust

Osiris-Rex's early data revealed a problem for the mission: Bennu is much rockier than NASA thought. Landing in a field of boulders puts a spacecraft at risk of tipping over and getting stranded.

To target the smoothest possible terrain on the asteroid, the Osiris-Rex mission team chose a landing spot that was much smaller than originally planned. Its leeway was just 26 feet (8 meters), whereas the initial plan expected it to have 164 feet (50 meters). That forced the spacecraft, which is about the size of a 15-passenger van, to target an area roughly equal to six parking spaces on the fast-spinning asteroid.

The landing spot was a relatively smooth area named Nightingale, which is covered in a fine rocky dust called regolith. This is the material that Osiris-Rex attempted to scoop up.

The spacecraft slowly descended about 3,280 feet (1 kilometer), maneuvering past a two-story boulder that mission controllers call "Mount Doom." Osiris-Rex had twice rehearsed this descent, practicing "basically everything except for the final two minutes," said Mike Moreau, a project manager.

The sequence went like this: The spacecraft's thrusters fired, pushing it out of its kilometer-high orbit above Bennu. Then the probe deployed its sample-collection arm and pointed its navigation camera to the asteroid's surface. About 3 1/2 hours later — and about 410 feet above the surface — the spacecraft fired its thrusters again to push itself toward the landing site. After another 10 minutes and another 260 feet of descent, the spacecraft burned its thrusters to maneuver into a precise landing spot.

If the spacecraft had detected hazardous rocks at its landing point, the probe would have initiated a back-away burn just 16 feet above the surface. But the whole operation seems to have gone according to plan.

The spacecraft appears to have reached Bennu's surface with its sample-collection arm stretched down. Assuming no snafus arose, this arm should have shot nitrogen gas out of a bottle to stir up the regolith beneath it. In the disturbance, some material was likely caught in the collection tool at the end of the arm.

Shortly after touchdown, Osiris-Rex fired its thrusters to push itself away from Bennu.

NASA will decide whether to stow the sample or try again

Once the spacecraft is back in Bennu's orbit, it will take a few days for NASA mission controllers to analyze the regolith sample it collected. If there's enough rock and dust, mission leaders will command the spacecraft to store the sample in a pod for its return to Earth.

But if the spacecraft has less than 2.1 ounces of regolith, it will try this whole sequence again in January, targeting a backup site on a different part of the asteroid.

"By far the most likely outcome that we will have on October 20 is we will contact the surface and come away with a large sample that exceeds our minimum requirements," Moreau said in September. "But Bennu has thrown us a number of curveballs."

Osiris-Rex was carrying three bottles of nitrogen for stirring up dust, allowing it three attempts to descend to Bennu's surface and collect a proper sample.

The Bennu sample should reach Earth in 2023

When Osiris-Rex returns to Earth in 2023, it's slated to shoot the capsule containing the samples into Earth's atmosphere. The samples should then parachute into the Utah desert for NASA to pick up.

"It's going to probably be Christmas in September," Lauretta said. "The best Christmas present I've ever had, these pristine samples from asteroid Bennu that I've been dreaming — literally dreaming — about for, at that point, almost 20 years of my life."

Scientists will set about analyzing the sample, but NASA will preserve some of the regolith for future study.

"These samples returned from Bennu will also allow future planetary scientists to ask questions we can't even think of today," said Lori Glaze, the director of NASA's Planetary Science Division, "and to be able to use analysis techniques that aren't even invented yet."

This story has been updated to reflect Osiris-Rex's successful landing on asteroid Bennu.