"The primary objective of the mission is to bring back 60 grams (2.1 ounces) of pristine carbon-rich material from the surface of Bennu."
US space agency NASA is poised Thursday to launch its groundbreaking first mission to a near-Earth asteroid to collect samples that could shed light on the dawn of the solar system.
Scientists hope the seven-year, $800 million mission will reveal something about the origins of the Bennu asteroid and of life itself.
The OSIRIS-REx spacecraft is scheduled to blast off Thursday at 7:05 pm (2305 GMT) from Cape Canaveral Air Force Station, near the Kennedy Space Center in Florida.
"The primary objective of the mission is to bring back 60 grams (2.1 ounces) of pristine carbon-rich material from the surface of Bennu," said Dante Lauretta, principal investigator of the mission and a professor of planetary science at the University of Arizona.
"We expect these samples will contain organic molecules from the early solar system that may give us information and clues to the origin of life."
The Lockheed Martin-made spacecraft will be carried aboard an Atlas V rocket made by United Launch Alliance, a 50-50 joint venture owned by Lockheed and Boeing.
Weather forecasters said there was an 80 percent chance of favorable conditions for the launch of the mission aimed at peering into the solar system's birth 4.5 billion years ago.
OSIRIX-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) is expected to reach Bennu in August 2018 and return to Earth with its bounty in 2023.
The asteroid is about 1,600 feet (492 meters) in diameter. "Think of it as a small mountain in space," Lauretta said.
Its 1.2-year orbit around the sun brings it closer to Earth every six years at a distance similar to the moon -- although there is very little chance Bennu could collide with Earth, according to estimates by the National Aeronautics and Space Administration.
The highest probability, one in 2,500, would occur between 2175 and 2196.
Once OSIRIX-REx reaches the asteroid in 2018, five instruments will map its surface using 3D laser imaging, identify the minerals and chemicals that may be on the surface, and select the sample site.
In July 2020, the spacecraft will touch Bennu -- but only for three seconds -- with a three-meter (3.3-yard) arm to collect rocks and dust using a device called the Touch-and-Go Sample Acquisition Mechanism (TAGSAM).
The TAGSAM is a type of reverse-vacuum device originally conceived by a Lockheed Martin engineer in his garage.
Sample returns in 2023
The space dust -- which may reveal how the materials necessary for life, such as carbon and ice, made their way to Earth -- will be stored in a capsule for the return journey.
The OSIRIS-REx will leave the asteroid in March 2021 and travel two and a half years to return to Earth in September 2023.
As the spacecraft nears our planet, the return sample capsule will be ejected and gently lowered to Earth by parachutes to an area southwest of Salt Lake City in the western state of Utah.
From there it will be transported to the NASA space center in Houston, Texas, where the materials will be analyzed.
The OSIRIS-REx will remain in orbit around the sun.
The mission will lay the groundwork for future explorations of asteroids and other small objects in the solar system, scientists say.
It could notably cast light on the widely accepted hypothesis that this type of asteroid brought water and other materials seen as necessary for life on Earth, they say.
Another aim of the mission is to measure the Yarkovsky effect, the sun's heating force on asteroids as they rotate that can cause them to drift widely over time.
A better understanding of this effect could help scientists more accurately predict the long-term risk of asteroids to Earth and divert the path of those threatening to collide with our planet.
In December 2014 the Japanese Aerospace Exploration Agency launched a similar mission, Hayabusa 2, which should reach an asteroid (162173 Ryugu) in 2018.
The Hayabusa 2 spacecraft will place on the space rock's surface a small lander named Mascot, produced by the French and German space agencies.
Its predecessor, Hayabusa, was supposed to study the effect of a crash landing on asteroid Itokawa and recover samples to bring back to Earth, but it only managed to bring back a few micrograms of material in 2010.
The European Space Agency succeeded in November 2014 to put its Philae lander on a comet, a space first. The lander transmitted 60 hours of data before running out of power.
Unlike the OSIRIS-REx mission, a return to Earth had not been planned.