NASA’s mission to collect samples from the OSIRIS-REx asteroid will contribute to a better understanding of how to protect humanity if Bennu’s path intersects with Earth.
The asteroid Bennu is 492 meters wide. Image: NASA.
Astronomers regard Bennu as a “precious gem,” but it also poses a considerable threat. According to Space, no asteroid is more likely to impact Earth within the next 200 years than Bennu. Discovered in 1999, Bennu is a rare type B asteroid rich in carbonaceous material, believed to contain chemical compounds dating back to the early days of the Solar System. Moreover, its 492-meter-wide orbit makes it the most dangerous object known to researchers within the Solar System.
Bennu is sizable enough to cause significant damage on Earth. If it were to collide with our planet, it would create a crater several kilometers wide on the surface. The impact would also generate earthquakes and shockwaves through Earth’s atmosphere, destroying buildings hundreds of kilometers away from the impact site.
The actual probability of Bennu colliding with Earth in the near future is very low. Models of Bennu’s trajectory and Earth’s orbit indicate a potential collision in 2182, with a 1 in 2,700 chance of impact. Even with adjusted models showing increased risk, engineers and scientists have ample time to devise a strategy to divert Bennu if necessary. Data collected by the OSIRIS-REx spacecraft will play a vital role in shaping this redirection mission.
When the OSIRIS-REx spacecraft landed on Bennu to collect samples in October 2020, the asteroid’s surface behaved unexpectedly. It turned out to be porous, almost like a sandy beach, nearly swallowing the spacecraft during its descent onto the Nightingale crater. This discovery highlighted the surprising low-density surface of the asteroid. The spacecraft sank about 50 cm into Bennu’s surface before the backup thruster fired. The emergency escape maneuver triggered another unexpected reaction, as images from OSIRIS-REx’s camera revealed a massive cloud of debris and dust billowing up, threatening the spacecraft as it retreated.
Currently, scientists are comparing the measurements taken from Bennu with data gathered during NASA’s DART (Double Asteroid Redirection Test) experiment, which successfully altered the orbit of the moonlet Dimorphos around the parent body Didymos in September 2022, according to Dante Lauretta, the principal investigator of OSIRIS-REx at the University of Arizona.
OSIRIS-REx’s in-depth study of Bennu from orbit has also revealed towering rock formations on the asteroid’s surface composed of porous, hole-filled material. Researchers believe that this porosity may shield Bennu from smaller impacts. As a result, there are fewer craters on Bennu’s surface than the research team initially expected based on historical asteroid collision knowledge within the Solar System. The unique material characteristics that make up Bennu could also influence how the asteroid responds to a redirection attempt to prevent it from colliding with Earth.