That will make Bennu the smallest object ever to be orbited by a spacecraft in space. The seven-year mission involved a close-up survey of the asteroid Bennu and collection of sample from Bennu's surface and return to Earth for study.
The arm has a full range of motion, with joints capable of movement comparable to shoulder, elbow and wrist joints.
There is also the possibility the asteroid sample could be rich in a valuable material that could be extracted for use on earth.
"Our CSIRO team in Canberra and our two sister Deep Space Network stations around the world in Spain and the United States will be with the mission every step of the way".
OSIRIS-REx is scheduled to return the sample to Earth in September 2023.
"Now that we've arrived, we will explore [Bennu's] surface through a series of flybys and orbital campaigns that allow us to determine which areas on Bennu are the safest and have material that can be ingested by our sampling mechanism", Daniella DellaGiustina of the University of Arizona told Sky and Telescope.
It is the first US attempt to gather asteroid samples for return to Earth, something only Japan has accomplished so far.
Some of Bennu sample will be held in reserve while the rest is subjected to two years of detailed analysis. 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.
Bennu is so small (about 0.05 percent of the mass of Mount Everest) that its gravity is almost negligible.
The asteroid could pass close to Earth, closer than the moon, in 2135, with even closer approaches possible in 2175 and 2195.
By expanding our understanding of asteroids, the mission could also help scientists to better understand the threat that asteroids may pose to humans on Earth.
'Bennu is likely rich in organic molecules, which are made of chains of carbon bonded with atoms of oxygen, hydrogen, and other elements in a chemical recipe that makes all known living things. It's because of objects like Bennu that these resources were delivered to Earth during its formation.
"For the past several months, Bennu has been coming into focus as I approached", the probe's Twitter account said. It is about 1,600 feet (488 meters) wide and most likely broke away from a larger asteroid between Mars and Jupiter a couple of billion years ago. This knocked it through space until an orbit close to Earth locked it in place.
OSIRIS-REx will spend the next year in orbit around its target before dropping down briefly so it can get close enough to scoop up a sample of dirt and rock from the surface.
This meeting will provide scientists with a rare window to look back at the beginnings of Earth's solar system, said Jay McMahon, an assistant professor in aerospace engineering at CU Boulder. "We work together to understand the history of the solar system".