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Nasa scientists learn more about asteroid Bennu’s future orbit

Chances of it hitting Earth are low, but Bennu remains one of the two most hazardous known asteroids in our solar system

This illustration provided by Nasa depicts the OSIRIS-REx spacecraft at the asteroid Bennu. (AP)

In a study released this week, researchers at Nasa used precision-tracking data from the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) spacecraft to better understand movements of the potentially hazardous asteroid Bennu through the year 2300. This not only significantly reduces the uncertainties related to its future orbit, but also improves scientists’ ability to determine the total impact probability and predict orbits of other asteroids.

According to a news release from the US space agency, asteroid Bennu will make a close approach with Earth in 2135. Although the near-Earth object will not pose a danger to our planet at that time, scientists must still understand Bennu’s exact trajectory during that encounter. This, in order to predict how Earth’s gravity will alter the asteroid’s path around the Sun – and affect the hazard of Earth impact. The study was published in Icarus, a scientific journal dedicated to the field of planetary science.

Also read: Asteroid samples from Hayabusa-2 leave Japan scientists speechless

“NASA’s Planetary Defense 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. “We carry out this endeavor 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.”

This undated image made available by NASA shows the asteroid Bennu from the OSIRIS-REx spacecraft.
This undated image made available by NASA shows the asteroid Bennu from the OSIRIS-REx spacecraft. (AP)

Kelly Fast, program manager for the Near-Earth Object Observations Program at NASA in Washington, explains in the release that the agency’s planetary defense mission is to find, monitor comets and asteroids that can come near Earth and may pose a hazard. Continuing astronomical surveys are used to collect data and discover previously unknown objects and refine orbital models for Nasa, Fast explains: “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.”

Scientists used NASA’s Deep Space Network, a global network of spacecraft communication ground segment facilities, and state-of-the-art computer models to significantly shrink uncertainties in Bennu’s orbit. They determined the asteroid’s total impact probability through the year 2300 is about 1 in 1,750 (or 0.057%). The researchers were also able to identify September 24, 2182, as the most significant single date in terms of a potential impact, with an impact probability of 1 in 2,700 (or about 0.037%), the release explains.

Before it left Bennu, the OSIRIS-REx spacecraft spent more than two years monitoring the asteroid, collecting vital information about its shape, composition, spin and orbital trajectory. The spacecraft also collected a sample of rock and dust from the asteroid’s surface, which it will deliver to Earth on September 24, 2023, for further detailed investigation. According to Davide Farnocchia, of the Center for Near Earth Object Studies, who led the study, scientists have never modeled an asteroid’s trajectory to this precision before. All this was possible because of the OSIRIS-REx data, he explains in the release.

In this image taken from video released by Nasa, the Osiris-Rex spacecraft touches the surface of asteroid Bennu on Tuesday, Oct. 20, 2020.
In this image taken from video released by Nasa, the Osiris-Rex spacecraft touches the surface of asteroid Bennu on Tuesday, Oct. 20, 2020. ( (NASA via AP))

The researchers were also able to determine how the asteroid’s orbit will evolve over time and if it will pass through a “gravitational keyhole” during its close approach in 2135. “These keyholes are areas in space that would set Bennu on a path toward a future impact with Earth if the asteroid were to pass through them at certain times, due to the effect of Earth’s gravitational pull,” the release explains.

To understand how where Bennu will be during its 2135 close approach – and whether it might pass through a gravitational keyhole – Farnocchia and his team evaluated various types of forces and factors: everything from the Sun’s heat, its gravity, and the gravity of other planets, their moons, and more than 300 other asteroids, among other factors. They even studied the force OSIRIS-REx exerted on the asteroid when performing its sample collection in October last year.

Also read: Can rockets and spacecraft change an asteroid's trajectory?

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