Supercomputer Takes on a Cosmic Threat

Supercomputer-created shock physics simulation of a 10 megaton nuclear device exploding at asteroid Golevka’s center of mass. The simulation provided realism in crack formation and propagation if the body were a single, solid rock with strength. Image CREDIT: Sandia National Laboratories

A super-powerful computer has simulated what it might take to keep Earth safe from a menacing asteroid.

Researchers have utilized the number-crunching brainpower of Red Storm--a supercomputer at Sandia National Laboratories in Albuquerque, New Mexico. Red Storm, a Cray XT3 supercomputer, is the first computer to surpass the 1 terabyte-per-second performance mark--a measure that indicates the capacity of a network of processors to communicate with each other when dealing with the most complex situations--in both classified and unclassified realms.

The massively parallel computing simulations have modeled how much explosive power it would take to destroy or sidetrack an asteroid that's got Earth in its cross-hairs.

For the computer runs, asteroid 6489 Golevka was chosen. Golevka isn't going to hit the Earth, explained Mark Boslough, a Sandia scientist and asteroid threat analyst. This particular asteroid was used as a "proxy" because solid geometry data about the object existed, he said.

Since its discovery in May 1991 by astronomer Eleanor Helin, asteroid Golevka has been repeatedly radar-scanned. It is roughly .33 mile (one half-kilometer) across, but tips the scales at about 460 billion pounds (210 billion kilograms), according to asteroid experts at the Jet Propulsion Laboratory in Pasadena, California.

The Golevka asteroid has been a particular object of interest since 2003. That's when NASA scientists discovered its course had changed.

Keeping tabs on Golevka has helped pin down the Yarkovsky Effect--a miniscule amount of force produced as the asteroid absorbs energy from the Sun and re-radiates it into space as heat. Over time--lots of it--that force can have a big effect on an asteroid's orbit.

Boslough said the actual geometry from radar measurements of asteroid Golevka were used in the computer simulations.

"Of course we don't know the internal structure so we had to assume something," Boslough said. He and his colleagues tried both heterogeneous and homogenous simulations, but selected the uniform strength and density for the high-resolution demonstration mainly for simplicity.

The researchers applied the Keep It Simple Stupid (KISS) principle of avoiding unnecessary complications--don't try the hardest thing first, Boslough added.

In general terms, several findings stood out in Red Storm computations that might be useful for future planetary defense systems.

Boslough first noted that there are two "end-member strategies" in the Golevka work:

• Deflection: Keeping the asteroid in one piece and changing its trajectory to miss the Earth; and

• Disruption: Blowing it to smithereens and making sure all the bits miss the Earth.  

"There are a range of in-between options," Boslough told SPACE.com, "but the deflection end of the spectrum is much more realistic." On a kiloton-per-kiloton basis, small, shallow explosions are much more effective for moving the asteroid than large, deep ones. 

One demonstration simulation--10 megatons at the center of mass of the object--is the most spectacular "end member" of the range that the research team explored--but is also the least likely scenario, Boslough explained. "It also neglects a fundamental problem of how you would get the device inside an asteroid."

Unlike Bruce Willis and his team drilling into the core of an asteroid in the 1998 movie Armageddon and planting a nuclear bomb, that scenario just doesn't seem likely, Boslough said.

Playing out Golevka's hypothetical demise even on a super-fast computer took longer than the movie. Sandia's half- second, billion-cell simulation of a 10-megaton explosion at Golevka's center took 12 hours to run on 7,200 processors of Red Storm.

The supercomputer is a product of a partnership between Cray Computers Inc. and Sandia National Laboratories, developed for the Advanced Simulation and Computing program of the Department of Energy's National Nuclear Security Administration (NNSA) laboratory.

The Red Storm computational output provided useful insights.

In particular, Boslough said, was the realization that using multiple, low-yield, deflecting explosions is much better than using one high-yield device. 

"There are many advantages" to this approach, Boslough observed. "For one, you don't need to rendezvous with the asteroid and drill a hole or otherwise place a devise. You can set it off as a surface burst. Contrast the time it takes to 'land' something on the surface of an asteroid--like NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft--to how long it takes just to get there, like NASA's Deep Impact," he said. 

You want to solve the problem quickly, Boslough said, "even if we know about an impact decades in advance--the public perception will be that time is of the essence."

If asteroid deflection is the game plan, there's need to avoid accidental breakage. 

A low yield blast lessens the volume of material that is subjected to the highest tensile and shear stress, reducing the likelihood that the object will come apart.

"If you do break the asteroid, you want to make sure none of the big pieces hit the Earth," Boslough said. "Multiple low-yield bursts over an entire hemisphere [of the asteroid] would reduce the likelihood that anything big would get left behind on the impact trajectory."

The fact that you can get a low-yield device to a menacing object fast also means that you are more likely to have a second chance, Boslough noted. That equates to a viable "backup plan", he added, for other, more elaborate, expensive, and time-consuming methods. 

"When you are saving the Earth, it's good to have a plan B. I suspect that if a Near Earth Object (NEO) were confirmed to be on an impact trajectory, public opinion would demand fast action and this would become plan A, if it wasn't already," Boslough said.

Boslough said that follow-on work regarding defending Earth from NEOs is slated. Specifically on tap is delving into momentum transfer for a variety of assumed asteroidal and cometary materials and structures.

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