Bennu is one of the most hazardous known asteroids in our solar system.
Thanks to a visit by a NASA spacecraft, scientists have a much greater understanding of the near-Earth asteroid, its upcoming closest approaches to Earth – and whether it could impact our planet.
While NASAs OSIRIS-REx mission spent more than two years orbiting Bennu, it was able to gather unprecedented information as well as a sample that is currently heading back to Earth.
The sample will arrive in September 2023.
The data collected by the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer allowed for precision tracking of the asteroids movements through to the year 2300 – findings that reduce the uncertainties scientists had about the asteroids future orbit.
While NASAs OSIRIS-REx mission spent more than two years orbiting Bennu, it was able to gather unprecedented information as well as a sample that is currently heading back to Earth. Credit: AP
The asteroid has a 1 in 1750 chance of impacting Earth through 2300.
The asteroid will make its next closest approach to Earth in 2135.
While Bennu wont come close enough to pose a threat to Earth then, knowing its exact trajectory can help scientists better understand how the gravity of our planet will change the asteroids future orbit around the sun.
This could also affect the chances of Bennu impacting Earth after 2135.
Bennu will make its most significant close approach on September 24, 2182, with a 1 in 2700 chance of impacting Earth on that day.
Bennu will make its most significant close approach on September 24, 2182, with a 1 in 2700 chance of impacting Earth on that day. Credit: dottedhippo/Getty Images/iStockphoto
The researchers agree that the risk of Bennu impacting Earth is low, and NASA will continue to observe the asteroids orbit for years to come.
A study based on the findings published Wednesday in the journal Icarus.
NASAs Planetary Defence mission is to find and monitor asteroids and comets that can come near Earth and may pose a hazard to our planet, said Kelly Fast, program manager for the Near-Earth Object Observations Program at NASA headquarters in Washington, in a statement.
We carry out this endeavour through continuing astronomical surveys that collect data to discover previously unknown objects and refine our orbital models for them.
The OSIRIS-REx mission has provided an extraordinary opportunity to refine and test these models, helping us better predict where Bennu will be when it makes its close approach to Earth more than a century from now.
Bennu is one of the most hazardous known asteroids in our solar system. Credit: AP
The OSIRIS-REx mission arrived at Bennu in December 2018 and departed earlier this year on May 10, loaded up with the sample it collected from the asteroids surface.
Even though the spacecraft is a couple of years from returning to Earth, it has been sending back data revealing what it learned about Bennu the entire time.
This allowed scientists to learn that its a rubble-pile asteroid shaped like a spinning top, composed of rocks bound together by gravity. Its about 500m wide.
The OSIRIS-REx data give us so much more precise information, we can test the limits of our models and calculate the future trajectory of Bennu to a very high degree of certainty through 2135, said lead study author Davide Farnocchia, a scientist at NASAs Centre for Near Earth Object Studies, in a statement.
Weve never modelled an asteroids trajectory to this precision before.
In this image taken from video released by NASA, the Osiris-Rex spacecraft touches the surface of asteroid Bennu on Tuesday, Oct. 20, 2020. Credit: AP
The Centre for Near Earth Object Studies, based at the Jet Propulsion Laboratory in Pasadena, California, can use asteroid data to calculate their trajectories, predict their future motion, and assess whether or not there is a possibility of an impact.
The orbits of asteroids around the sun change over time, and the smallest things can shift them.
Specifically, the researchers wanted to determine whether Bennu will experience a gravitational keyhole during its first close approach to Earth in 2135.
A gravitational keyhole is a small region of space where a planets gravity can alter the orbit of a passing asteroid.
If Bennu passes through one of these at a certain time due to Earths gravity, it could set Bennu on the course for a future impact with our planet.
Thanks to a visit by a NASA spacecraft, scientists have a much greater understanding of the near-Earth asteroid, its upcoming closest approaches to Earth – and whether it could impact our planet. Credit: XtockImages/Getty Images/iStockphoto
If Bennu does pass through a gravitational keyhole, then the gravity of the Earth would tweak the motion of Bennu by just the right amount to put it on a collision trajectory at a later date in the 22nd century, Farnocchia said.
Prior to this study, scientists were concerned that Bennu could have 26 potential gravitational keyholes to pass through. Now, they are only concerned about two of them.
But we should keep in mind that the impact probability, overall is really small, Farnocchia said.
In fact, there is a 99.94 per cent probability that there is not an impact trajectory. So, there is no particular reason for concern.
The suns heat can cause something called the Yarkovsky effect on asteroids.
As asteroids orbit the sun, they repeatedly heat and cool as they rotate.
As the asteroid spins through this temperature shift, it releases energy, and the asteroid gets a small bit of thrust.
The Yarkovsky effect will act on all asteroids of all sizes, and while it has been measured for a small fraction of the asteroid population from afar, OSIRIS-REx gave us the first opportunity to measure it in detail as Bennu travelled around the Sun, said study coauthor Steve Chesley, a senior research scientist at NASAs Jet Propulsion Laboratory, in a statement.
The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid – tiny, yes, but significant when determining Bennus future impact chances over the decades and centuries to come.
A supplied image obtained Wednesday, March 20, 2019 showing asteroid Bennu ejecting particles from its surface on January 19. Credit: NASA/GODDARD/UNIVERSITY OF ARIZONA/LOCKHEED MARTIN/PR IMAGE
Other forces can alter the movement of asteroids, including the gravity of the sun, other planets, moons and other asteroids.
Dust in the solar system and the charged stream of particles from the sun, called the solar wind, can also affect Bennus orbit.
And during the OSIRIS-REx mission, the team was surprised to observe Bennus surface ejecting particles into space, which could also play a role.
While the target goal of the mission was to collect a sample from Bennu and return it to Earth, the insight gained into near-Earth asteroids and achieving better calculations of their orbits is crucial.
The orbital data from this mission helped us better appreciate Bennus impact chances over the next couple of centuries and our overall understanding of potentially hazardous asteroids – an incredible result, said Dante Lauretta, OSIRIS-REx principal investigator and professor at the University of Arizona, in a statement.
Bennu is one of the most hazardous known asteroids in our solar system.