Bennu, an asteroid with a small chance of crashing into Earth in the 22nd century, has inspired an unprecedented feat of cosmic reconnaissance from NASA.
The U.S. space agency estimates Bennu will come close enough to Earth and pose a 1-in-2,700 chance of impacting the planet between the years 2175 and 2196. "Put another way, those odds mean there is a 99.963 percent chance the asteroid will miss the Earth. Even so, astronomers want to know exactly where Bennu is located at all times," NASA explained in a press release.
NASA launched an unmanned spacecraft in September 2016 to study Bennu and the possible impact it could have on Earth. OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer) spent two years traveling 1.2 billion miles (1.9 billion kilometers) toward Bennu and eventually reached the asteroid two years later.
In December 2018, OSIRIS-REx switched from flying toward to Bennu to orbiting 11.8 miles (19 km) around it, and on Dec. 31 it entered the asteroid's orbit — making Bennu the smallest object ever to be orbited by a spacecraft.
In the following months, OSIRIS-REx conducted flyovers as it set new records for the closest orbit of a planetary body by a spacecraft. On June 12, it performed a maneuver that brought it within just 2,231 feet (680 meters) of Bennu, or about 0.4 miles above the surface. The previous record, also set by OSIRIS-REx, was about 0.8 miles (1.3 km). This kicked off a new phase of the mission, called Orbital B, that will involve mapping the asteroid's entire surface to find the best sampling site. The main goal is to analyze the asteroid's mass and spin rate. Then, NASA hopes to briefly touch Bennu's surface in order to collect a sample. This sampling is scheduled for summer 2020, with OSIRIS-REx delivering the sample back to Earth in 2023.
Why is NASA so interested in this asteroid?
Bennu may offer additional insights into the formation of our solar system.
"On planets like Earth, the original materials have been profoundly altered by geologic activity and chemical reactions with our atmosphere and water," said Edward Beshore, deputy principal investigator for OSIRIS-REx. "We think Bennu may be relatively unchanged, so this asteroid is like a time capsule for us to examine."
If Bennu were to crash into Earth, scientists estimate the asteroid's impact would be 4,000 to 5000 times more powerful than the Chelyabinsk meteor that dramatically exploded over Russia in 2013. While certainly not a world-threatening event (it's estimated that it would take an object 60 miles wide to completely wipe out life on Earth), Bennu's impact on an urban population center would likely be catastrophic.
"If astronomers someday identify an asteroid that presents a significant impact hazard to Earth, the first step will be to gather more information about that asteroid," added Beshore. "Fortunately, the OSIRIS-REx mission will have given us the experience and tools needed to do the job."
Editor's note: This article has been updated with new information since it was originally published in August 2016.