As Steven Spielberg's movie Deep Impact thrills audiences with a fictional account of what would happen if an asteroid collided with Earth, scientists are using the fastest supercomputer to model an impact with a 1.4km asteroid.

Using their extensive experience in modelling shock waves and incorporating virtual reality techniques, scientists at Sandia have just completed the largest hyper-velocity impact simulation ever performed.

Impact scars on Jupiter

In 1994, Sandia scientists simulated the impact of the fragmented comet Shoemaker-Levy 9 into the cloud decks of Jupiter.

They were later to see their predictions come true as the Hubble Space Telescope watched the real impacts.

The asteroid was targeted 40km south of New York.

Within seconds, the asteroid is vaporised, the ocean floor deformed and hundreds of cubic kilometres of molten rock and superheated steam are thrown into the atmosphere.

New York is flattened. Millions are dead.

Nuclear winter

The simulation takes into account the velocity of the incoming asteroid, its make-up and strength, the densities of the atmosphere, the oceans and rock as well as the physics of shock waves.

Following the impact a shock wave would race around the Earth. In North America the heat would incinerate cities and forests almost instantaneously.

Some debris thrown up into the atmosphere would come raining down hours later. Other debris would remain in the upper atmosphere for longer.

The debris in the high atmosphere would reflect the sun's light and the world's temperature would lower. A global snowstorm may follow initiating a "nuclear winter".

Simulation of the point of impact (Sandia)

"A lot of major breakthroughs in science are going to come from these kinds of calculations," Boslough says.

He adds that computer simulations are a safe way to see what would happen during an impact. "It is almost like doing an experiment - one you could never do. One you would never want to do."

The recent short-lived news story about the possible impact of an asteroid with the Earth in 2028 sparked intense scientific and popular interest world-wide.

Shortly after the initial alarmist statements it was shown that the asteroid in question would not hit our planet.

However, the United States National Research Council says in a report - started before the recent asteroid story - that astronomers should find new ways to release such information and avoid scare stories.

Some 400 Earth-approaching asteroids and comets larger than 1km in diameter have been detected so far but this is estimated to be just 10% of the total number of potentially threatening objects out there.