Asteroid DA14's close flyby with Earth: How bad would an impact be?

Asteroid 2012 DA14 is set to zip by so close to us that it will pass between the Earth and our weather satellites on Friday afternoon, traveling at nearly 8 kilometres per second.
An artist's rendering of the estimated blast radius for the ground impact of a 2.9 megaton asteroid if it were to hit downtown Hamilton. (Kevin Gamble/Alex Wellerstein)

A nine-tonne meteor streaked across the sky above Russia's Ural Mountains Friday morning, causing sharp explosions and injuring hundreds of people. An even bigger chunk of space rock about the size of a jet plane is set to zip between the Earth and our weather satellites on Friday afternoon, and while NASA says we're not in any danger of a catastrophic collision, it's hard not to wonder what would happen if we were.

Meteors typically cause sizeable sonic booms when they enter the atmosphere because they are traveling much faster than the speed of sound. Injuries on the scale reported Friday in Russia, however, are extraordinarily rare.

The contrail of a meteorite is seen over the village of Bolshoe Sidelnikovo on Friday morning. The resulting shockwave injured hundreds on the ground in Russia, many of them hurt by broken glass. (Nadezhda Luchinina, E1.ru/AP)

Asteroid 2012 DA14, due to make its closest approach to Earth around 2:24 p.m. ET today, won't enter the planet's atmosphere. But it's predicted that the 45-metre diameter, 130,000-tonne asteroid will pass closer to Earth than any object its size has come in decades.

At its closest point it will be 27,700 kilometres from the planet's surface — a mere tenth of the distance between the Earth and the moon.

At that time, it will be zooming by at about 28,100 kilometres per hour or 7.82 kilometres per second relative to Earth.

"It's a record close approach," said Robert Cockcroft, manager of McMaster's WJ McCallion Planetarium. "An object of this size gets this close only once every 40 years or so."

DA14 was discovered in February of 2012 and has been tracked since then. The asteroid's orbit is so well known that "there's no chance of a collision," said Donald Yeomans, manager of NASA's Near Earth Object Office.

Meteor, meteoroid, or meteorite?

Small pieces of space debris — usually parts of comets or asteroids — that are on a collision course with the Earth are called meteoroids. When meteoroids enter the Earth's atmosphere they are called meteors. Most meteors burn up in the atmosphere, but if they survive the frictional heating and strike the surface of the Earth they are called meteorites.

Nor is it likely to hit any satellites. It's too close to Earth to collide with the geosynchronous satellites, but a lot further out than the bulk of Earth's orbiting satellites, including the International Space Station, which is located 386 kilometres above the surface.

NASA estimates that asteroids this size fly this close to the Earth about once every 40 years and hit the planet roughly once every 1,200 years. The last time it happened was on June 30, 1908, when a meteorite crashed in Tunguska, Russia.

North Americans won't be able to see asteroid DA14, Cockroft says, as it's set to sail over the Indonesian region. Even there it won't be possible to see it with the naked eye, but amateur astronomers do have a shot at spotting the asteroid with a telescope — though the object's rapid speed could make that a difficult task, Cockcroft said.

The worst case scenario

But what if an asteroid this size was to someday strike a built-up area, such as Hamilton in Southern Ontario's Golden Horseshoe region?

Cockcroft says the impact would be something like the event in Tunguska, Russia, back in 1908. It leveled trees over a 2,124-square-kilometre territory.

How common are meteor strikes?

Experts say smaller strikes happen five to 10 times a year. Large impacts such as the one Friday in Russia are rarer but still occur about every five years, according to Addi Bischoff, a mineralogist at the University of Muenster in Germany. Most of these strikes happen in uninhabited areas where they don't cause injuries to humans.

Read more about meteors.

However, estimates put the Tunguska meteor at around 100 metres, which is more than double the size of 2012 DA14.

But as Cockroft points out, that asteroid struck an uninhabited stretch of Siberia — so the collateral damage was largely confined to trees and land masses. If DA14 were to hit downtown Hamilton, the results would be catastrophic.

"It would create a very large impact crater and flatten everything in the downtown region," Cockcroft said.

Shockwaves would emanate through the ground and be felt for kilometres. A "compression wave" of force would also push through the air, toppling buildings and blowing out windows, he added.

"You would have to evacuate the entire city of Hamilton and surrounding areas — maybe even much of southern Ontario," he said, in order to avoid massive casualties.

Heat derived from the rock's entry into the Earth's atmosphere and the kinetic impact with the planet would likely cause fires throughout the city, too.

"With oxygen and fuels everywhere, things could spontaneously start igniting," he said.

Hamilton wouldn't fare much better if the asteroid struck Lake Ontario.

"Then we'd have to worry about a giant tsunami created on the lake," Cockcroft said. "It would be like a solid mass of water coming towards you."

A drifting orbit

While DA14 has been coming relatively close to Earth about twice a year, that's about to change, NASA's Yeomans said at the press conference Thursday. As it flies by, the Earth's gravity will actually perturb the asteroid's orbit, shaving a couple of months off its usual 12-month travel time around the sun.

"It won't come back in the Earth's neighbourhood anywhere near as frequently as it has in the past," he said. "The Earth is going to put this one into an orbit that is considerably safer than the orbit it has been in."

Cockcroft says NASA is monitoring "millions of pieces of debris right now" that are less than 100 metres in diameter. "It's a laborious process, but in the end it could save us all," he said.

He also lamented that asteroids are only viewed for their destructive capacity, when they also have the ability to help give rise to life.

"They were the things that brought the things to Earth that were needed to form life, like water and carbon," he said.

"There is no denying their destructive side. But they also helped create life on Earth."

Earth's close encounter

–Courtesy STK animation courtesy of Analytical Graphics, Inc