In a kiss-like maneuver, the spacecraft's robotic arm will collect some material from Bennu's surface, then sling the sample back toward Earth.
For the past two years, the OSIRIS-REx spacecraft has sailed across the solar system by the light of the stars. Like ancient mariners and the Apollo astronauts, it needed the constancy of the constellations to navigate the dark unknown.
All that changed Monday, when the NASA probe finally reached its target, an Empire State Building-sized asteroid called Bennu.
Now OSIRIS-REx faces a whole new kind of challenge: exploring the smallest object ever orbited by a spacecraft.
Sitting at mission control at the Denver offices of Lockheed Martin, which operates the spacecraft for NASA, engineer Javi Cerna waited for the signal indicating OSIRIS-REx had begun the burn needed to bring it close to its target.
"Standby for Bennu arrival," Cerna announced.
He fidgeted in his chair, then stood. The room was utterly silent.
Then Cerna grinned and spread his arms out wide
We have arrived!"
OSIRIS-REx was within 12 miles of Bennu's surface - about the distance between the White House and NASA's Goddard Space Flight Center, which manages the spacecraft.
Soon an image of the asteroid appeared on the mission control screens: a diamond-shaped body with a rough, speckled exterior. OSIRIS-REx was finally at the doorstep of its new home.
Bennu is a carbonaceous asteroid - a primitive, carbon-rich piece of debris left over from the process that formed the solar system 4.6 billion years ago. OSIRIS-REx will spend the next 18 months there, surveying the landscape and probing Bennu's chemical makeup before finally selecting what piece of the asteroid it wants to bring back home. In a kiss-like maneuver, the spacecraft's robotic arm will collect some material from Bennu's surface, then sling the sample back toward Earth. It will be the largest planetary sample retrieved since the Apollo era, when astronauts brought rocks back from the moon.
Studying the sample in terrestrial labs, scientists hope to uncover clues about the birth of the planets and the origins of Earth's water and life. They may also uncover potentially useful natural resources such as organic molecules and precious metals. And since Bennu has a 1-in-2,700 chance of impacting Earth about 200 years from now, researchers figure it would be good to glean some insights about the asteroid's fate - and how it might intersect with our own.