On March 8 an asteroid between 40 and 80 meters in diameter passed with 480,200 kilometres of Earth. No one saw it until four days later.
In 1908, something about the same size blasted into the atmosphere above the Tungaska forest in Siberia in 1908 and exploded with force of 15 million tons of TNT, incinerating or knocking flat thousands of square kilometers of forest. Had it hit a heavily populated area, it could have killed hundreds of thousands. The next such object might.
Asteroids are rocky and/or metallic objects that orbit the Sun. They can be as small as a pebble or as large as Ceres, which has a diameter of 1000 kilometres. The recently completed Infrared Space Observatory Deep Asteroid Search suggests between 1.1 million and 1.9 million asteroids one kilometer or more in diameter can be found in the asteroid belt between the orbits of Mars and Jupiter; others wander the solar system, including several hundred whose orbits cross Earth’s. There must be millions–even billions–of smaller asteroids.
It’s generally thought asteroids are material that, during the formation of the Solar System, never coalesced into a planet. The examination of meteorites (small asteroids that have survived the plunge through Earth’s atmosphere) reveals that 92.8 percent are composed of stone, 5.7 percent are composed of iron and nickel, and the rest are a mixture of the stone, iron and nickel. Presumably, this holds true for asteroids in general.
What would happen if a large asteroid hit the Earth? Well…it wouldn’t be pleasant.
An asteroid 1.5 kilometers in diameter would cause damage unprecedented in human history, affecting the climate by injecting water vapor and dust into the atmosphere, and possibly severely damaging the ozone layer (because the impact would send up a plume of nitrogen oxide).
A much larger asteroid, say 6.5 kilometres in diameter, could darken the sky so much photosynthesis would become impossible and plants would die. Fragments of the asteroid and the Earth hurled into space by the impact would rain down all over the planet, setting forest fires. The resulting smoke would further darken the atmosphere, plunging the world into permanent night. The temperature would plummet.
Just ask the dinosaurs. There’s a vast, buried crater in the Yucatan peninsula, believed to be the mark left by the impact of a 10-kilometre-wide asteroid 65 million years ago that many scientists believe played an important role in the dinosaurs’ extinction.
But you don’t have to go to the Gulf of Mexico to see evidence of asteroid bombardment. Deep Bay, a circular bay 13 kilometres wide off Saskatchewan’s own Reindeer Lake, is thought to be the crater left behind by an asteroid impact around 100 million years ago.
NASA estimates that the risk of a collision with a large asteroid is about 1 in 5,000 over the next century. (Just a note for 6/49 lottery players: that means an asteroid is 2,800 times more likely to hit in the next century than you are to win the lottery this week. Just thought you’d like to know.)
One possible threat is an asteroid called 1950 DA, first discovered in 1950 and just recently spotted again by astronomers. Comparing data from the 1950 and more recent observations have allowed them to predict that there is a chance (less than one in 300) that the kilometer-wide asteroid will collide with Earth on March 16, 2880.
With that kind of warning, we have time to think of possible solutions. Maybe we could deflect it with nuclear weapons. Or maybe there’s an even better way. One influence on an asteroid’s path is the Yarkovsky effect, a slight pressure caused by the reflection of sunlight. Maybe we could darken the asteroid or coat it with a shiny substance to influence this effect. Calculations indicate that changing the amount of light 1950 DA reflects could move it as much as 1,400 kilometres in 100 years.
But to have any chance to do anything, we have to know that an asteroid is approaching. Because the threat is real, as March’s near-miss shows, governments have been asked to fund scientific surveys of asteroids that cross Earth’s orbit. It’s estimated that advances in astronomical imaging systems could allow us to catalog all asteroids larger than one kilometre in diameter within 10 years for just $50 million.
Astronomers would like to see it happen. And in view of the long-long-range forecast for March 16, 2880 (possibility of kilometer-sized hail), so would I.
