Thwarting Giant Asteroids Headed To Earth: Lawrence Livermore Lab

LIVERMORE, CA — If a massive asteroid gets on a collision course with Earth, researchers at Lawrence Livermore National Laboratory now have a better understanding of how we might deflect it.

Actually, there is a remote chance that a giant — scientists have named it "101955 Bennu" — could cross paths with Earth more than a century from now. Researchers aren’t really all that concerned with a Bennu collision, but the large asteroid — which measures 500 meters wide — does offer an ideal study subject of how effective different deflection technologies might be, according to LLNL.

Bennu has been used as a guinea pig twice. One case study found that a "kinetic impactor" — similar to using a spacecraft as a battering ram — would not deflect a Bennu-sized asteroid.

But an interagency team of researchers led by LLNL has completed the first ever in-depth investigation into how an asteroid would respond to a nuclear deflection attempt. Results: "A standoff nuclear impulse would be effective in deflecting Bennu and protecting life on Earth," according to LLNL.

The research was published online in Acta Astronautica and will appear in print in early 2020.

“The whole purpose of studies like this is to help us shorten the response timeline if we were to see something coming at us,” said physicist Megan Bruck Syal, who is the LLNL planetary defense team lead and an author on the paper. “We don’t want to have to scramble to figure out whether to use an impactor or a nuclear device on a particular asteroid. These studies help us define those thresholds.”

Unlike popular portrayals of a nuclear deflection mission — like the movie “Armageddon” — the nuclear deflection approach would consist of detonating a nuclear explosive some distance from the asteroid, according to LLNL. This would flood one side of the asteroid with X-rays, vaporizing a layer of the surface, which would create rocket-like propulsion as vaporized material is ejected from the asteroid, researchers said.

“The nuclear option would be the key to deflecting large asteroids,” said Dave Dearborn, LLNL physicist and lead author on the paper. “It also offers flexibility that impactors don’t. For instance, the amount of energy deposited into an asteroid with a nuclear device can be tuned by adjusting how far it is from the asteroid when detonated.”

Researchers estimate that it would take a minimum of 7.4 years before a nuclear impulse could be delivered to Bennu. This includes the time it would take to build the spacecraft, plan the mission and travel to the object. Assuming the impulse was successfully delivered, it would take many years for the small change in speed to accumulate into a sufficient change in a giant asteroid's trajectory, according to LLNL.

It would take many decades of lead time to change Bennu's trajectory, according to the researchers. Even more uncertainty exists for other space objects that do not regularly pass close enough to Earth for radar observation.

There are more than 20,000 "near-Earth objects" (NEOs) found by NASA so far, and scientists estimate that this is just a fraction of the total NEO population, according to LLNL.

A U.S. Congress-defined goal to discover and track the orbits for 90 percent of NEOs greater than 140 meters in diameter is likely years from completion.

“Time would be our No. 1 enemy,” Bruck Syal said. “That’s why it’s critical that we advance our ability to detect threats through future space-based telescopes like NEOCam, which would be dedicated to hunting down NEOs. We also want to shorten the timeline for making a mitigation decision and launching a deflection mission. The chances of a Bennu-class collision appear slim now, but they aren’t zero and the consequences could be devastating if we aren’t able to act in time. In the end, our ability to protect people and critical infrastructure on Earth could come down to how ready we are to respond quickly.”