Asteroid tsunami: How scientists warned impact could ‘send 400 feet waves to US coast’

Dr Ward and Dr Asphaug's study was conducted as part of a general effort to provide a rational assessment of asteroid impact hazards. 

Dr Asphaug, who organised a NASA-sponsored scientific workshop on asteroids in 2002, noted that asteroid risks are interesting because the probabilities are so small while the potential consequences are enormous. 

Also, the laws of orbital mechanics make it possible for scientists to predict an impact if they are able to detect the asteroid in advance.

He said: “It's like knowing the exact time when Mount Shasta will erupt.

"The way to deal with any natural hazard is to improve our knowledge base, so we can turn the kind of human fear that gets played on in the movies into something that we have a handle on."

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For the simulation, the researchers chose an impact site consistent with the orientation of the Earth at the time of the predicted encounter – in the Atlantic Ocean about 360 miles from the US coast.

Dr Ward explained that the 60,000-megaton blast of the impact could vaporise the asteroid and blow a cavity in the ocean 11 miles across and all the way down to the seafloor, which is about three miles deep at that point. 

The blast also excavates some of the seafloor, it was claimed. 

Water would then rush back in to fill the cavity, and a ring of waves sent out in all directions. 

He said: ”In the movies, they show one big wave, but you actually end up with dozens of waves. 

“The first ones to arrive are pretty small, and they gradually increase in height, arriving at intervals of 3 or 4 minutes.”

Two hours after impact, the study claimed 400-foot waves would reach beaches from Cape Cod to Cape Hatteras, and by four hours after impact, the entire East Coast would experience waves at least 200 feet high.

It would take eight hours for the waves to reach Europe, where they would come ashore at heights of about 30 to 50 feet.

At its greatest estimates, NASA predicted asteroid 1950 DA represents a risk 50 percent greater than that of any average hazard from the present era to the year 3000.

But since 2003 the estimates have been updated several times, with the latest, in 2015, placing the odds at one in 8,300 (0.012 percent) to occur.

Despite this, the space agency has reiterated more will be known after its next close approach on February 5, 2021.

Updating the risk is necessary because not enough is known about the physical properties of the asteroid.

For example, radar data suggests two possible directions for the space rock’s spin pole. 

If one pole is correct, solar radiation acceleration could significantly cancel thermal emission acceleration, meaning probability would then be close to the maximum 0.33 percent. 

If the spin pole is instead near the other possible solution, there would be little chance of collision. 

NASA says the situation is similar to knowing you have a coin that is biased so one side will land up 80 percent of the time – but you don’t know which side. 

You can only say that when you flip the coin, the chance of heads is 80 percent or 20 percent.

Occasionally, asteroids can also make “close approaches” to Earth, but this does not mean they are likely to strike.

NASA says: “As they orbit the Sun, NEOs can occasionally approach close to Earth.

“Note that a ‘close’ passage astronomically can be very far away in human terms, millions or even tens of millions of kilometres.

“Occasionally, asteroids' orbital paths are influenced by the gravitational tug of planets, which cause their paths to alter.”

A force known as the Yarkovsky effect can also cause an asteroid to veer off-course.

The effect occurs when a space rock is heated in direct sunlight and cools down to release radiation from its surface. 

NASA added: “This radiation exerts a force on the asteroid, acting as a sort of mini-thruster that can slowly change the asteroid's direction over time.”

There is also the possibility of asteroids or fragmented asteroids, being redirected towards us after colliding with other space rocks. 

But other asteroids listed on NASA’s database of “Earth close approaches” are deemed safe and NASA’s tracking systems have ruled out all possibility of danger. 

NASA previously said: “Because of the ongoing search efforts to find nearly all the large NEOs, objects will occasionally be found to be on very close Earth approaching trajectories. 

“Great care must then be taken to verify any Earth collision predictions that are made. 

“Given the extremely unlikely nature of such a collision, almost all of these predictions will turn out to be false alarms. 

“However, if an object is verified to be on an Earth colliding trajectory, it seems likely that this collision possibility will be known several years prior to the actual event.”