If We Blow Up an Asteroid, It Might Put Itself Back Together

Despite what Hollywood tells us, stopping an asteroid from creating an extinction-level event by blowing it up may not work.

The New York Times

By Robin George Andrews

March 8, 2019

Faced with the prospect of a sizable asteroid heading toward Earth and causing doomsday, humanity has come up with various responses.

Hollywood may reckon that the best way to destroy an errant space rock is with nuclear weapons. This is rarely the preferred option of experts, but using some sort of spacecraft system to smash an asteroid into small, harmless pieces is seen as a real-world possibility. A new study, looking at a gigantic space rock-on-space rock clash, hints at how utterly ineffective this type of asteroid assassination attempt may be.

Using computer models, scientists simulated a 4,000-foot asteroid smashing into a 15.5-mile asteroid at 11,200 miles per hour. Immediately after colliding, the large asteroid cracked considerably, with debris flowing outward like a cascade of Ping-Pong balls. Despite some deep fractures, the heart of the asteroid was not comprehensively damaged.

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As time went on, the gravitational pull of the asteroid’s resilient core was able to pull back ejected shards. It seems that asteroids don’t just absorb mind-boggling amounts of damage, but, as previous work has hinted, they also are able to rebuild themselves.

Charles El Mir, who studies asteroid annihilation at Johns Hopkins University and is the paper’s lead author, said his findings “could be interpreted as an argument against ‘blowing up’ an asteroid as a defensive strategy.”

Asteroid collisions and demolitions have been simulated many times in recent decades. Earlier studies suggested that large asteroids are full of internal scars because of their violent history, and that a fast enough impact would completely shatter them.

The new study, published this month in the journal Icarus, tried a different simulation.

K.T. Ramesh, director of the Hopkins Extreme Materials Institute, said that Andy Tonge, a former graduate student, had developed a computational model that looked at how materials like bulletproof vests respond to impacts. Realizing that Dr. Tonge’s model could simulate asteroid impact events, the team merged it with another model that also replicated the effects of a large asteroid’s gravitational field.

This hybrid model allowed them to more realistically see how an asteroid responds to being hit by a powerful projectile. It captured previously missing but vital small-scale details, including where fractures would appear and precisely how they would spread.

Michele Bannister, a planetary astronomer at Queen’s University Belfast, described the research as “a nice upgrade on modeling the complex physical realities” of the solar system’s enigmatic rocky monsters.

The study has limitations. Both asteroids are modeled as simple, nonrotating chunks of rock, whereas real asteroids are far more variable. In addition, the larger asteroid, despite featuring a starting collection of cracks, did not have a history of multiple impacts as true asteroids would. A large space rock smashing into a humongous space rock also differs from a missile onslaught, or an atomic bomb exploding on or beneath an asteroid’s surface while a popular rock band plays.

The study doesn’t rule out using projectiles to destroy an incoming asteroid, Dr. El Mir said. But, he added, shattering a large asteroid may end up causing more problems than it solves. Turning a cannonball into shotgun-shell fragments could still result in Armageddon if the shards strike Earth.

NASA’s Planetary Defense Coordination Office, which keeps an eye on asteroids and comets that will one day pass close to Earth, instead suggests changing a space rock’s trajectory by giving it a small nudge well in advance of reaching our world. NASA and others aim to test this strategy in 2022 with the Double Asteroid Redirection Test, in which a spacecraft will deliberately crash into the smaller member of a binary asteroid system in an attempt to change its orbit around the larger body.

Ultimately, the choice between deflection and destruction largely depends on how quickly an incoming asteroid is spotted.

“A successful deflection becomes more difficult to execute as warning time decreases,” said Megan Bruck Syal, a planetary defense researcher at the Lawrence Livermore National Laboratory. “For the shortest warning times, robust disruption and dispersal of the fragments may be the only viable option to prevent the impact.”