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NASA successfully tags asteroid Bennu: What you need to know about the mission

The Osiris-Rex spacecraft attempted to swipe souvenirs from Bennu on Tuesday to bring home to Earth. Soon we'll know how successful it was.

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Artist's conception of NASA's Osiris-Rex spacecraft and the asteroid Bennu.

NASA/Goddard/University of Arizona

Editors' note: Osiris-Rex has touched down on Bennu. Our coverage of the event is here. Our answers to questions about the mission are below.

NASA's Osiris-Rex spacecraft briefly touched down on a large asteroid Tuesday to snag some rocks and dust from its surface to be returned to Earth for study. On Wednesday, NASA revealed the first batch of images. The event marks a major first for NASA and a boon for science, space exploration and our understanding of the solar system. 

The touch-and-go, or TAG, sample collection of asteroid 101955 Bennu was deemed a success at around 3:12 p.m. PT. NASA broadcast the TAG maneuver live on NASA TV and the agency's website. You can find a video at the end of this piece. For answer to your mission questions, read on. 

When did the mission begin?

Osiris-Rex as a concept has been in existence since at least 2004, when a team of astronomers first proposed the idea to NASA. After more than a decade of development, the spacecraft launched from Cape Canaveral, Florida, on Sept. 8, 2016, atop an Atlas V rocket from United Launch Alliance, a joint venture of Lockheed Martin and Boeing. The spacecraft spent the next 26 months cruising to Bennu, officially arriving on Dec. 3, 2018.

Since then, the mission team has spent nearly two years orbiting the diamond-shaped space rock, surveying and mapping its surface to select the best sampling spot. In recent months, rehearsals led up to the sample collection attempt. 

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Why Bennu?

Bennu is what's called a "rubble pile" asteroid, meaning it was formed in the deep cosmic past when gravity slowly forced together remnants of an ancient collision. The result is a body shaped something like a spinning top with a diameter of around one-third of a mile (500 meters) and a surface strewn with large rocks and boulders. 

Bennu is thought to be a window into the solar system's past: a pristine, carbon-rich body carrying the building blocks of planets and of life. Some of these resources, such as water and metals, could also be worth mining at some point in the future for use on Earth or in space exploration. 

The asteroid has one other characteristic that makes it particularly interesting to scientists, and humans in general. It has a chance of impacting Earth in the distant future. On NASA's list of impact risks, Bennu is ranked No. 2. Current data shows dozens of potential impacts in the final quarter of the 22nd century, although all only have a minute chance of actually happening. 

How does TAG work?

For anyone who's ever dabbled with robots or maybe even entered a robotics competition, the Osiris-Rex mission would seem to be the ultimate culmination of a young roboticist's dreams. The touch-and-go sampling procedure is a complex, high-stakes task that's been building to a key climactic moment for years. If it succeeds, it will play a role in history and our future in space. 

The basic plan was for Osiris-Rex to touch down on Bennu at a rocky landing site dubbed Nightingale. The van-size spacecraft would need to negotiate building-size boulders around the landing area to touch down on a relatively clear space that's only as large as a few parking spaces. However, a robotic sampling arm was the only part of Osiris-Rex to actually set down on the surface. One of three pressurized nitrogen canisters was fired to stir up a sample of dust and small rocks that could then be caught in the arm's collector head for safe keeping and return to Earth. 

The descent to the surface of Bennu took roughly four hours, about the time it takes the asteroid to make one full revolution. After this slow approach, the actual TAG sample collection procedure remarkably lasted only a few seconds. 

Preparing for TAG did not go exactly as planned. Mission organizers initially hoped the surface of Bennu would have plenty of potential landing spots covered primarily with fine materials comparable to sand or gravel. It turns out the surface of Bennu is extremely rugged with no real welcoming landing spots. 

After spending much of the last two years reevaluating the mission, the team decided to try "threading the needle" through the boulder-filled landscape at Nightingale.

It's all paid off, so far. Osiris-Rex was able to touch down, but we won't know for sure if it collected a sample until later in October. Fortunately, if the tag was unsuccessful, the spacecraft can try again. It's equipped with three nitrogen canisters to fire and disrupt the surface, which means the team gets up to three tries at nabbing a sample. 

Then what?

Immediately after collecting its sample, Osiris-Rex fired its thrusters to back away from Bennu. The spacecraft will continue to hang around above Bennu for the rest of 2020 before finally performing a departure maneuver next year and beginning a two-year journey back to Earth. 

On Sept. 24, 2023, Osiris-Rex is scheduled to jettison its sample return capsule, which will land in the Utah desert and be recovered for study. 

Hasn't this been done before?

Yes. Japan's Hayabusa spacecraft successfully returned tiny grains of the asteroid 25143 Itokawa to Earth in 2010. Its successor, Hayabusa-2, fired a special copper bullet at the large asteroid Ryugu in 2019 and then retrieved some of the shrapnel. That sample is on its way back to Earth.  

How can I watch? 

The CNET Highlights channel covered the event live. You can rewatch the stream below: