NASA’s OSIRIS-REx asteroid sample collection mission will help scientists understand better how to protect humanity in case Bennu’s path intersects with Earth.
Asteroid Bennu is 492 meters wide. Photo: NASA
Bennu is a precious yet potentially perilous space rock. According to Space, no other asteroid has a higher likelihood of hitting 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 chemicals from the early days of the solar system. Moreover, its 492-meter-wide orbit makes it the most hazardous object known to researchers.
Bennu is large enough to cause severe damage to Earth. If it were to collide with our planet, it would create a crater several kilometers wide. Such an impact would generate earthquakes and shockwaves through Earth’s atmosphere, demolishing structures hundreds of kilometers away from the impact site.
The actual likelihood of Bennu colliding with Earth in the near future is very low. The flight path model of Bennu and Earth’s orbit indicates a potential collision in 2182, with a probability of 1 in 2,700. Even if further adjustments to the model suggest increased risk, engineers and scientists have ample time to devise strategies for deflecting Bennu. Data collected by the OSIRIS-REx spacecraft will play a crucial role in shaping a mission to alter Bennu’s course if necessary.
When the OSIRIS-REx spacecraft touched down on Bennu to collect a sample in October 2020, the asteroid’s surface didn’t react as expected. Rather than being solid, the site of the landing site, known as Nightingale, was more like quicksand, nearly swallowing the spacecraft. This revealed surprisingly low surface density. The spacecraft sunk 50 cm into Bennu’s surface before its backup thruster fired to escape. This emergency action triggered another unexpected response. Images captured by the OSIRIS-REx camera showed a massive cloud of rocks and sand shooting up, posing a threat to the retreating spacecraft.
Currently, scientists are comparing the measurements from Bennu with data obtained during NASA’s Double Asteroid Redirection Test (DART) experiment, which successfully altered the orbit of the moonlet Dimorphos around the parent body Didymos in September 2022, according to Dante Lauretta, the OSIRIS-REx research group leader at the University of Arizona.
OSIRIS-REx’s in-depth study of Bennu from orbit also revealed towering boulders on the asteroid’s surface, constructed from porous, hole-ridden materials. Researchers suggest that this porosity may serve as a protective mechanism against smaller impacting objects. Consequently, there are fewer craters on Bennu’s surface than the research team initially anticipated, based on their understanding of asteroid impacts in the history of the solar system. The peculiar material properties comprising Bennu may also affect how the asteroid responds to a deflection mission aimed at preventing a collision with Earth.