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Sandia Scientists Predict What An Asteroid Strike Would Look Like

Sandia National Laboratories

Media contact:
John German, jdgerma@sandia.gov, (505) 844-5199

Technical contacts:
David Crawford (hypervelocity impact physics),
dacrawf@sandia.gov, (505) 845-8975

Arthurine Breckenridge (3-D computer visualization),
arbreck@sandia.gov, (505) 845-8390

News Release: May 5, 1998

Real (not reel) deep impacts: Sandia scientists predict what an asteroid
strike would look like, really

ALBUQUERQUE, N.M. -- Steven Spielberg's new blockbuster movie -- with its
computer-animated interpretation of a comet striking Earth -- promises to be
a big hit at the box office this summer. But computer scientists at Sandia
National Laboratories are creating some big hits of their own these days that
they think may better approximate a real asteroid catastrophe.

Using virtual reality techniques, decades of experience in shock physics,
advanced computer programs, and the world's fastest computer, the scientists
have completed in recent weeks one of the largest hypervelocity impact
physics calculations ever performed.

In the latest computing scenario, an asteroid 1.4 kilometers in diameter
strikes the Atlantic Ocean 25 miles south of Brooklyn, N.Y. To model the event
the scientists broke up a 120-square-mile space that roughly approximates the
New York City metropolitan area, the air above, and the water and earth below,
into 100 million separate cubes, or grids. Sandia's teraflops supercomputer
then calculated what happened inside each cube as the asteroid splashed down.
The cubes were reassembled to produce a three-dimensional moving picture of
the collision. The teraflops, currently the world's fastest computer, performs
more than one trillion mathematical operations per second.

The simulation is no video game; the calculations take into account the real-
world laws of physics governing time, temperature, pressure, gravity, the
densities of water and earth, and hundreds of other considerations to create
an accurate prediction. What's more, the resulting computer simulation can be
explored using interactive virtual reality techniques. For instance, scientists
can "fly through" the 3-D movie to get a better idea of what's happening on
Coney Island if they want.

The work supports Sandia's Department of Energy mission to use the world's
highest-performance computers to develop computer codes that can one day model
the extremely complex physics that occur during a nuclear weapon blast. In the
absence of real-world nuclear testing, DOE and the weapons labs are developing
continually more powerful supercomputers and computer codes to simulate the
complex 3-D physics involved in nuclear-weapon performance and to accurately
predict the degradation of nuclear weapon components as they age in the
stockpile. Simulating comet impacts provides an opportunity to test and
improve the codes.

How did Spielberg do?

So what would happen during such an impact, really? According to the
simulation, the impact would vaporize the asteroid, deform the ocean floor,
and eject hundreds of cubic miles of superheated water vapor, melted rock, and
other debris into the upper atmosphere and back into space. Much of the debris
would then rain down over the world for the next several hours and also form a
high global cloud, says David Crawford of Sandia's Computational Physics and
Mechanics Department. The shock wave from the impact would level much of the
New England region. The heat would incinerate cities and forests there
instantaneously. The global cloud would then lower temperatures worldwide, and
a global snowstorm likely would ensue and last several days to several weeks,
initiating a "nuclear winter" that would create more hardships for earth's
inhabitants.

An impact of this magnitude can be expected to occur on Earth about once every
300,000 years and approximates what scientists consider to be the "global
catastrophe threshold," he says.

So how close is Spielberg's interpretation of the event to the teraflops'
virtual predictions?

"The movie makers didn't have the benefit of the world's fastest computer, but
they produced superior visuals that appear remarkably realistic," says
Arthurine Breckenridge of Sandia's Computer Architectures Department.

In the movie preview, the comet strikes at an angle and raises a symmetrical
steam cloud, she says, which probably wouldn't happen. "We now know that the
vapor cloud produced by an impact is initially asymmetric, sending more
material in the direction of the ricochet." The movie does realistically depict
a tsunami that would surely follow an ocean impact, she says.

Spielberg's Deep Impact opens this Friday, May 8. Another movie, Armageddon,
which depicts an asteroid "the size of Texas" threatening to strike Earth,
opens July 1.

An experiment you would never want to do

The teraflops simulations employ "massively parallel computing," a computing
approach pioneered by Sandia in the late 1980s. In massively parallel computing,
thousands of discrete computing tasks are assigned to several hundred separate
computing "processors" inside the supercomputer. The computing tasks are
accomplished simultaneously and their results reassembled. All of today's high
performance supercomputing employs a massively parallel approach.

In the most recent 100-million-cell calculation, the teraflops used 8,192 of
its 9,000 processors. The entire calculation lasted 18 hours. Sandia has done
similar calculations on its high performance computers, including a 54-million-
cell simulation of a comet striking the ocean. In 1994, Crawford and Sandia
scientist Mark Boslough accurately simulated what would happen when Comet
Shoemaker-Levy 9 plunged into Jupiter's atmosphere. Months later, the world's
astronomers watched the Sandia-predicted event unfold in real life through the
Hubble space telescope.

"A lot of major breakthroughs in science are going to come from these kinds of
calculations," Boslough says. He notes that the impact simulations are
something that can't be done any other way. "It's almost like doing an
experiment -- one you could never do. One you would never want to do."

Sandia's teraflops computer is a joint development of DOE, Sandia, and Intel.
It represents the initial goal of DOE's Accelerated Strategic Computing
Initiative, a ten-year program designed to move nuclear weapons design and
maintenance from a test-based to simulation-based engineering approach.

Sandia is a multiprogram Department of Energy laboratory operated by Lockheed
Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif.,
Sandia has research and development programs contributing to national defense,
energy and environmental technologies, and economic competitiveness.

----------------------------------------------------------

The simulations in Quick Time format, other illustrations, and links to
information about other Sandia comet modeling work are available at
http://sherpa.sandia.gov/asteroid/

A video tape containing the simulation and other Sandia comet-modeling work is
available from Sandia's media relations office; call (505) 844-5199.

PHOTO CAPTIONS: [http://www.sandia.gov/media/comethit.htm]

[Comet hit simulation image 1]
This computer-generated image by Sandia National Laboratories' scientists shows
the impact of a 1-km comet (or asteroid) hitting in the open ocean. The comet
and 300 to 500 cubic kilometers of ocean water would be vaporized nearly
instantaneously by the tremendous energy of the impact. The impact energy of
about 300 gigatons of TNT would be equivalent to about 10 times the explosive
power of all the nuclear weapons in existence in the 1960s at the height of the
Cold War.

[Comet hit simulation image 2]
Five seconds after a 1.4 kilometer-wide asteroid crashes into the Atlantic
Ocean off the coast of New York, an impact plume containing superheated water,
earth, and other debris blankets major portions of Long Island. The viewpoint
is from orbital altitude from a location about 100 kilometers west of New York
City looking east. Long Island trails off in the distance. Manhattan and Staten
Islands are in the foreground.

[Comet hit simulation image 3]
Eleven seconds after impact, Long Island and the New York shoreline are engulfed
in debris and superheated steam, and much of the material in the upper portions
of the impact plume is on suborbital trajectories. In both images, water is
blue, land is brown, water vapor is white, and hot material (greater than 5,000
Celsius) is orange.