Bennu is a 500-meter-wide asteroid that circles our solar on a path that takes it dangerously near to Earth on a regular basis.
According to Icarus, NASA scientists utilized new data and complicated computer models to estimate the exact course of the Bennu asteroid for the next 300 years. The possibility of an asteroid impact, which could create a 3-to-6-mile-wide crater and pack the energy of more than 1.1 billion tons of TNT for an asteroid the size of Bennu, is of particular interest.
“An object Bennu’s size impacting in the Eastern Seaboard states would pretty much devastate things up and down the coast.” NASA’s planetary defense chief Lindley Johnson told reporters.
There is a Low Likelihood of an Asteroid Impact
Fortunately, the chances of Bennu hitting Earth are low: roughly a 1 in 1,750 (or 0.057 percent) chance between now and 2300. The date with the greatest likelihood of a collision is September 24, 2182, when Bennu has a 1 in 2,700 (approximately 0.037 percent) chance of colliding with Earth.
While these figures are somewhat higher than prior predictions, any worry should be mitigated by the enhanced capacity to anticipate the passage of near-Earth objects correctly. This increases the likelihood that humans will ultimately be able to change the movement of such items if required.
OSIRIS-REx Delivers Unprecedented Accuracy
According to NASA, accurate forecasts for the Bennu asteroid were made feasible by data from the agency’s OSIRIS-REx probe, which stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer. Bennu was founded in 1999, and comparative approaches with Earth were studied using ground-based telescopes in 1999, 2005, and 2011. OSIRIS-REx was started in 2016 and arrived at Bennu in December of 2018.
OSIRIS-REx hovered around Bennu like a hummingbird for about two and a half years, snapping images and collecting data on its size, shape, mass, and composition, as well as tracking its spin and orbital course. It was continually sending data back to Earth via NASA’s Deep Space Network of massive radio antennae during that period. It was frequently able to determine Bennu’s position within a few meters. This is a remarkable feat, given that the radius of its orbit is around 168 million kilometers.
Small Forces Can change Asteroid Trajectories
Because asteroids are far smaller than planets, their paths are influenced by many tiny factors, including solar heat. The asteroid Bennu spins around its axis, altering which parts are exposed to the sun. As sun-warmed portions spin into darkness, they cool and emit infrared radiation, generating a tiny amount of push.
Steve Chesley, a senior research scientist who was engaged in the study, said:
“The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid — tiny, yes, but significant when determining Bennu’s future impact chances over the decades and centuries to come.”
Bennu has been drifting by 934 feet each year due to this influence.
The impact of gravity from the sun, planets, moon, Pluto, and more than 300 asteroids in the asteroid belt are also included in the computations. The drag induced by the solar wind was also incorporated, as was the influence of Bennu’s habit of ejecting particles from its surface, which NASA described as unexpected.
Finally, researchers examined the impact of OSIRIS-REx sampling Bennu’s surface in October 2020. This final effect proved insignificant, which is good news for future asteroid expeditions.
Encounters with the Earth
The data obtained by OSIRIS-REx enabled scientists to compute the course of the Bennu asteroid with a high degree of precision until 2135, outperforming earlier projections by a factor of 20. There is no risk of an asteroid impact from Bennu until 2135 when the trajectory predictions become less certain due to a significant event.
Bennu will be closer to Earth than the moon in September 2135 (approximately 123,000 miles from the Earth’s surface, compared to 238,900 miles from the Earth to the moon). Depending on when and where Bennu makes this near approach, Earth’s gravitational pull may cause Bennu’s orbit around the sun to vary just enough for it to smash with Earth at a later period.
Computer models have discovered the tiny areas of space through which Bennu would have to traverse in September 2135 to set up a potential collision with Earth. The size of these 26 “gravitation keyholes” ranges from a few hundred feet to a few miles. Researchers ruled out Bennu passing through 24 of these keyholes using data from OSIRIS-REx. Two of the keyholes are still open.
Astronomers will be keeping a careful eye on this event in September 2135 and adjusting estimations for possible future repercussions. That gives civilization about 50 years to prepare for an impact in September 2182. By that time, the knowledge and technology accessible should be remarkable. Unfortunately, that occurrence is two lifetimes away.
Nonetheless, there will be fascinating events to look forward to long before then. OSIRIS-REx departed Bennu in May 2021 and is scheduled to drop a 4.5-billion-year-old rock sample onto Utah’s desert in September 2023. According to The New York Times, NASA will try to push the Didymos asteroid sufficiently to change its route in 2022. Didymos offers no imminent danger and is just around one-third the size of Bennu, but this expedition will see whether humanity can avoid an asteroid collision.
To present, scientists have cataloged about 26,000 near-Earth asteroids, including over half of the asteroids of Bennu’s size (more than 140 m). We can only speculate on what remains uncovered until an additional study is completed.
