Deflecting an asteroid will be harder than scientists thought

March 4 (UPI) -- According to new asteroid collision models designed by scientists at Johns Hopkins University, deflecting a large rock headed for Earth will be harder than previously thought.

Using the most up-to-date findings on rock fracturing, researchers developed computer models to more accurately simulate asteroid collisions.

"Our question was, how much energy does it take to actually destroy an asteroid and break it into pieces?" Charles El Mir, a mechanical engineer at Johns Hopkins, said in a news release.

The results, detailed this week in the journal Icarus, suggest the task is quite difficult.

"We used to believe that the larger the object, the more easily it would break, because bigger objects are more likely to have flaws," El Mir said. "Our findings, however, show that asteroids are stronger than we used to think and require more energy to be completely shattered."

Scientists used small rocks in lab experiments to study asteroid collisions, but accurately scaling the dynamics of violent space rock collisions has proven difficult. Nearly two decades ago, researchers developed collision models to measure the effects of a rock's mass, temperature, and material brittleness on its potential to fracture.

The first high-speed rock collision simulations suggested an asteroid 15 miles across could be easily destroyed by an asteroid measuring just a half-mile in diameter traveling at 180 miles per hour.

Over the last decade, scientists have slowly made improvements to asteroid collision models by accounting for more detailed rock fracturing processes ignored by the earliest simulations.

For example, the first asteroid collision models failed to accurately account for the slow speeds at which cracks in asteroids develop.

For the newest study, scientists decided to divide the model into two phases. Phase one modeled the immediate fracturing that happens in the wake of a collision -- the processes that play in a matter of seconds. The second phase simulated the gravitational re-accumulation process that happens over the course of several hours or days.

The first phase of the updated model showed a large asteroid is not destroyed by a much smaller asteroid. Instead, millions of cracks form throughout, the core fractures and a crater is left behind. During phase two, the fractured core exerts a strong gravitational pull on the smaller pieces of debris and shrapnel broken during the impact.

Because the asteroid did not crack completely during phase one, the space rock retained significant strength.

If scientists are going to develop an asteroid deflection strategy that can actually work, they need to know how much force it really takes to destroy or deflect one. The latest study -- published in the newest issue of the journal Icarus -- showed it's more force than was originally thought.

"We are impacted fairly often by small asteroids, such as in the Chelyabinsk event a few years ago," said K.T. Ramesh, director of the Hopkins Extreme Materials Institute. "It is only a matter of time before these questions go from being academic to defining our response to a major threat. We need to have a good idea of what we should do when that time comes -- and scientific efforts like this one are critical to help us make those decisions."