Will 500 meter asteroid Bennu hit Earth in next century? NASA investigates

The near-Earth asteroid 101955 Bennu is one of the two most hazardous known asteroids in the solar system, along with 1950 DA. Right now, Bennu poses no threat and is very far from Earth. This is in line with prior predictions by NASA, which found that the Earth was at zero risks of an asteroid impact within the current century.

But in 2135, just a little over a century away, Bennu will begin making a closer approach to Earth. At the time, it still won't pose a threat, but it is essential to study whether the Earth's gravity will change the asteroid's path around the sun, and maybe even bring it close to striking the planet.

This is exactly what NASA sought to answer in its new study, the findings of which were published in the academic journal Icarus.

Using precision-tracking data from the agency's Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft, NASA was able to better study the asteroid and its movements through the year 2300.

Using this model, the scientists significantly shrank uncertainties in its orbit, with the asteroid having a chance of 1 in 1,750 (around 0.057%) of impacting the planet through 2300. The date with the highest chances of actually having an impact scenario is September 24, 2182, with the chance being 1 in 2,700 (around 0.037%).

The data was gathered by the OSIRIS-REx spacecraft, which spent some two years in close proximity to Bennu before leaving on May 10, 2021. A sample of rock and dust from the asteroid will be sent to Earth for study on September 24, 2023.

The big concern had about Bennu was that it could pass through what is known as a "gravitational keyhole" in 2135, as doing so at certain times could set it on a collision course with Earth. However, the studies have not yet shown any likelihood that it would become a serious risk, though the risk itself remains, even if incredibly small.

But if it did impact, the damage would be, according to one estimate, the equivalent of 1,200 megatons of TNT. For comparison, the Little Boy nuclear bomb dropped on Hiroshima in 1945 was around 0.015 megatons of TNT.

The asteroid is also set for a close approach to Earth in 2060, but it is unlikely to cause damage and will be too far away to see with common binoculars. 

An asteroid impact remains one of the most dangerous possible natural disasters that could occur, however unlikely. It is for this reason that Astronomers around the world, including NASA's Planetary Defense Coordination Office (PDCO), work to monitor all nearby asteroids and calculate their trajectory to see if any of them pose a threat to the planet.

Some, such as NASA's PDCO and John Hopkins University's Double Asteroid Redirection Test (DART) Mission, seek to find ways to counter possible asteroid impacts, this one, in particular, seeking to fire a spacecraft at an asteroid to utilize speed and its impact to alter an asteroid's trajectory ever so slightly, enough to throw it off course.

Or, in layman's terms, punching it with a rocket with enough speed to change its direction by a fraction of a percent.

This project is set to be tested soon, on an asteroid far away from the planet. However, a more immediate possible solution was proposed by Airbus, which would see TV satellites essentially hijacked and repurposed in order to deflect an asteroid – and this solution could only take a few months to get ready and launch.

Regardless, NASA and other organizations keep a watchful eye on the sky for any asteroids nearing the planet, including the use of special "asteroid hunter" telescopes.