The sample, no mere piece of rubble, will revolutionize scientists' understanding of these flying space rocks, which are believed to hold clues to how the Solar System formed billions of years ago.
"The reason there’s so much interest in asteroids is a lot of them are very primitive, from when the Solar System formed, and they didn't change with wind and water, or weather like on Earth," Amy Simon, a planetary scientist at NASA's Goddard Space Flight Center, tells Inverse. "They're still more pristine than anything you could find in the universe."
This landmark achievement for science took place Tuesday at 6:11 p.m. Eastern, as the world watched OSIRIS-REx touch down down on Bennu and extend its robotic arm to scoop up the sample. It marks NASA's first attempt to not only land on an asteroid, but also return a sample of these curious bodies back to Earth.
OSIRIS-REx's mission was carried out in three steps. The spacecraft's checkpoint burn began its steep descent towards the surface of the asteroid. After ten minute of descending towards Bennu, OSIRIS-REx then conducted a matchpoint burn maneuver, which changed the spacecraft's flight path to match the rotation of Bennu so that it could target the landing site.
Finally, OSIRIS-REx touched down on Bennu at 6:11 p.m. Eastern and collected a sample before backing away from the asteroid.
It was a dramatic climax to a mission that launched in 2016. OSIRIS-REx has been orbiting asteroid Bennu since December, 2018. The spacecraft is equipped with six instruments designed to map the asteroid, document the sample site, and collect other data and observations of Bennu.
Now that it has the sample in hand, the spacecraft will store the precious cargo until it can be dropped off on Earth — hopefully in 2023. The mission is perhaps the most ambitious sample return attempt since astronauts brought back samples of the Moon during the Apollo mission.
"Bennu represents an important class of asteroids, it's a laboratory of early Solar System formation," Michael Daly, an associate professor at York University's department of physics and astronomy, tells Inverse. "[These asteroids] relatively haven’t been touched since the early Solar System."
The road to Bennu — There are 500,000 known asteroids in the Solar System. Of these, there are just 192 that have a low-eccentricity orbit similar to Earth's, and only 26 of those asteroids have diameters larger than 200 meters, which meant they don't spin so fast as to cause material to fall off.
Of these 26 asteroids, just five, including Bennu, are known to be rich in carbon.
Bennu orbits the Sun every 436.6 days. It is a rare, B-type asteroid — the most primitive kind of asteroid. Bennu has barely changed since it formed 4 billion years ago, and it contains relatively high amounts of carbon, organic molecules, and amino acids — considered to be the building blocks of life.
Most of what we know about asteroids come from meteorites, which rain down to Earth as their parent comets and asteroids pass our planet. But this material may be significantly altered by virtue of Earth's atmosphere. The material on Bennu, however, is pristine — untouched by Earth's atmospheric conditions, water, or weather.
Another reason why scientists study asteroids is due to their potential threat.
Bennu comes within a mere 0.002 Astronomical Units to Earth every six years, and there is a slight chance it will collide with our planet in about 150 years. Therefore, studying Bennu's orbit and the small forces that affect its trajectory can help scientists create better models of these rocky bodies' trip around the Sun and their chances of colliding with the Earth.
Delicate operations — The road to Bennu has not been easy.
In March, the plan to land on Bennu took a twist. Scientists discovered Bennu’s surface was more hazardous than they first thought, and covered in large boulders, some the size of buildings. Originally, the plan was for OSIRIS-REx to land within a 164-feet touchdown area. But a new navigation method was needed to land the spacecraft on a far smaller site of about 52-feet wide — 10 percent of the original safe zone.
Mark Fisher, Lockheed Martin’s lead OSIRIS-REx spacecraft engineer, compared the team's work to reconfigure the spacecraft's landing remit while it was in space to attempting to perform surgery on one's self.
"It takes a while and it's very challenging," Fisher tells Inverse. "You can't let the spacecraft stop doing what it's doing."
NASA’s mission control created a 3D map of Bennu's topography to document how high the rocky boulders are, and how deep the asteroid’s craters go. The navigation system used that data, in addition to real-time images taken during the landing attempt, to guide the spacecraft.
After collecting the sample, OSIRIS-REx stored it in a 2.6-foot-long canister, which Fisher describes as like a clam shell that closes up tight on the journey back to Earth. The spacecraft itself won't be returning to Earth — rather, the 'clam shell' will be dropped off, landing (hopefully) in the middle of the desert in Utah. There, scientists can collect it and begin their studies.
"As we fade away from the asteroid, the priority is to protect that sample," Fisher says.
OSIRIS-REx will begin its return back to Earth in March of 2021. Before it leaves Bennu, it will collect data and more pictures of the asteroid — scientific souvenirs for the road home.