When Bennu has the best chance of hitting Earth


NASA / Goddard

In 2135, the asteroid Bennu will perform a close flyby of the Earth. The gravity of our planet will alter Bennu’s path, making it a challenge to calculate his future path.

While the University of Arizona-led OSIRIS-REx mission studied and sampled the asteroid Bennu, it also helped scientists calculate if – or when – the half-mile body will ever crash. on the ground.

Their findings appear in the journal Icarus.

September 24, 2182: Over the next 300 years, this is when Bennu has the best chance of hitting Earth: around 0.05%.

To figure this out, the team factored in everything from hundreds of gravitational hits to tiny surges from surface heating and particle ejection.

“Just like the photons from the heat transfer pulse to the asteroid, the ejection of particles from its surface can also have an effect,” said Dante Lauretta, the University of Arizona planetary scientist who directs the mission.

This matters because even a small variation in where or when Bennu passes between Earth and the moon in 2135 could have a big influence on his way back in 2182.

“The cases where Bennu aligns perfectly to become an impactor, we call that a keyhole. So if he’s in exactly the right place at the right time, Earth’s gravity will essentially launch him. Fifty years later, it’s coming back to touchdown, ”Lauretta said.

Bennu is only a fraction of the size of the body that wiped out the dinosaurs. It is also not known whether the bulk conglomerate, or “rubble heap”, would shatter upon entering Earth’s atmosphere. But anyway, the total energy would stay the same.

“I like to say, ‘Would you rather be hit by a cannonball or a shot from a shotgun?’ Because that’s what’s going to happen when Bennu breaks up in the atmosphere: the pieces will spread over hundreds of kilometers, and you will have smaller impacts, but spread over a much larger area, ”he said. Lauretta said.

Launched in 2016, OSIRIS-REx (the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) reached Bennu in 2018, where he studied the composition, mass, structure and temperature of the planetary fragment. In 2020, the craft carried out a tactile sample of one kilogram of surface material, which it will deliver by parachute into the Utah desert in September 2023.

After that, Lauretta’s team hopes to expand the craft’s operations.

“Once the spacecraft releases the sample return capsule, that vehicle is still very capable. All of the science instruments are mostly functional. And so we thought, where else could we go?” said Laurette.

One possible destination: 99942 Apophis, another asteroid that was once believed to be on a collision course with Earth. Scientists now know that Apophis is intended for a flyover, not a flyby, but the 340-meter asteroid will pass very close to Earth in 2029.

Flight dynamics calculations also allow OSIRIS-REx to be in the vicinity.

“We can design our gravitational assistance so that a few weeks later the spacecraft meets the asteroid,” Lauretta said.

The plan must first pass NASA’s main exam, in which teams will detail their plans and the agency will decide whether or not to fund an extension until 2030.


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