Future Asteroid That Threatens Earth May Be Near-Indestructible, Scientists Warn

A future asteroid that threatens Earth may be near-indestructible, scientists concluded in a new study that offered some "aggressive" solutions for what to do if we ever face one. 

Scientists who studied tiny specks of dust recovered from a potentially hazardous asteroid  discovered that “rubble-pile” asteroids, which are loose conglomerations of smaller space rocks, are much more common and robust than previously assumed, a finding that suggests it might take nuclear devices to push them off course from Earth, should the need arise.

In 2010, Japan’s Hayabusa mission stunned the world by becoming the first spacecraft to successfully deliver pristine samples from an asteroid back to Earth. The trailblazing mission collected about 1,500 grains of dust from the surface of Itokawa, a rubble pile asteroid about the same size as the Eiffel Tower that is considered potentially hazardous because its path through space crosses Earth’s orbit.

Now, scientists led by Fred Jourdan, the director of the Western Australian Argon Isotope Facility at Curtin University, have used Itokawa’s dust particles to show that the asteroid may have formed over 4.2 billion years ago from the shattered remains of a “monolithic asteroid,” a type of space rock that is much denser than rubble piles. 

This surprisingly long lifespan indicates that rubble pile asteroids are far tougher than previously assumed, a finding that may necessitate the use of “more aggressive approaches (e.g., nuclear blast deflection)” to knock them off course in the event of a possible collision, according to a study published on Monday in Proceedings of the National Academy of Sciences. 

“Monolithic-type asteroids that are more than a kilometer in diameter have been predicted to have a lifespan of a few 100 million years,” Jourdan and his colleagues said in the study. “However, the durability of rubble pile asteroids is currently not known.” 

“This study shows that the formation age of the rubble pile Itokawa asteroid is older than 4.2 billion years,” they added. “Our results suggest that rubble piles are probably more abundant in the asteroid belt than previously thought and provide constraints to help develop mitigation strategies to prevent asteroid collisions with Earth.”

Jourdan and his colleagues reached this conclusion after examining three dust particles from Itokawa, each of which measures about 150 microns—about the same size as a grain of table salt. The team zoomed in on the tiny grains with spectroscopic instruments and used dating techniques to show that Itokawa has survived catastrophic collisions for almost the entire history of the solar system.

It seems counterintuitive that rubble piles, which are half-empty collections of loose boulders, would be so much tougher than hefty monolithic asteroids. However, a rubble pile asteroid is akin to a “giant space cushion,” Jourdan said in a statement, allowing these rocks to take punch after punch without accruing much damage. 

As a result, rubble piles are probably a lot more common than expected—especially small asteroids under 600 feet—raising the odds that one might crash into Earth in the future. If we were to detect one of these rocks before it hit, we could potentially push it off course by crashing an impactor into it, though we might need to break out the big guns to do it. 

Porous asteroids like Itokawa ”are harder to deflect by kinetic impact since porosity decreases the efficiency of the transfer of momentum,” the team noted in the study. “Here, we showed that small rubble pile asteroids can survive billions of years against the ambient bombardment in the inner solar system due to their resistance to collisions and fragmentations.”

“Therefore, more aggressive approaches (e.g., nuclear blast deflection) might have a higher chance of success against rubble pile asteroids,” the researchers said. This approach would involve setting off a nuclear blast near the asteroid and using the shockwave to redirect its trajectory.

The team noted that NASA’s Double Asteroid Redirection Test (DART) mission, which intentionally crashed into a rubble pile asteroid last year, will help scientists to understand how to protect humanity from these rocks. In addition to securing a safe future for our civilization, Hayabusa’s samples continue to reveal amazing new details about the evolution of Earth, and the solar system. 

“Even though most particles recovered from Itokawa’s surface regolith have a diameter significantly smaller than 100 microns, they provide an invaluable means to study early solar system processes such as the formation of Earth’s oceans and the formation, evolution, and longevity of rubble pile asteroids,” the team noted in the study.

Moreover, Hayabusa’s successor, Hayabusa 2, also returned samples from a rubble pile asteroid in 2020, and NASA’s OSIRIS-REx mission is currently headed back to our planet with its own asteroid haul. These precious deliveries from outer space will continue to expand our understanding of our cosmic past, and help us to preserve our future in a tumultuous universe.