What an ability to defend against asteroids will mean for humanity

Earth is a constant target of random debris cast off by comets and blasted out of other celestial bodies. Now, we may be in a position to start doing something about it.

Most of what hits us is harmless. Meteorites don’t often cause damage, and they’re relatively rare compared with the thousands of tons of cosmic dust that rain down harmlessly every year. But then there are other forms of space rubble, like the 42 asteroids scientists recently rendered in unprecedented detail – a couple of which are longer than the Grand Canyon.

A spacecraft launched last week in the US is meant to help us prepare for something similar heading in our direction. If all goes to plan, it will crash into an asteroid 11 million kilometers away next September, knocking the rocky planetoid into a new orbit.

That should demonstrate our ability to nudge anything truly threatening off course. It would also mark the first time we’ve altered the movement of a natural celestial object.

NASA describes this Double Asteroid Redirection Test (DART) as a “planetary defense” exercise. The European Space Agency will follow with a 2024 launch to conduct a “crash scene investigation” of DART’s aftermath.

The annual probability of an asteroid striking Earth that can destroy a city is an estimated 0.1%. For an impact similar to what wiped out the dinosaurs ever occurring, it’s 0.000001%.

Still, best to prepare for the worst.

A few years ago, NASA announced that its catalog of known, near-Earth asteroids had topped 15,000. It added that none of them posed a risk of impact with Earth for the next century.

But NASA also said that while it located many of the bigger asteroids, there were still “a lot more” of the smaller but potentially hazardous type yet to be found.

Asteroids orbit the sun, and most exist between the orbits of Mars and Jupiter. Most meteorites are chunks broken off asteroids in that region, and meteors are asteroids or meteorites that burn up in Earth’s atmosphere – though the shockwaves they generate can do significant damage.

There’s plenty of natural debris out there with the potential to cross Earth’s path in a meaningful way. But some of what may come raining down on us in the near future is actually our own doing.

As many as 400 tracked, man-made objects enter Earth’s atmosphere every year. Some argue it might be prudent to curb the growing pool of man-made space junk that’s the source of these objects, as we better prepare for a disastrous collision with the natural variety.

And there is ample precedent for the natural variety.

66 million years ago, an asteroid believed to have been about 10 kilometers wide crashed into Earth. Its impact likely kicked up a metallic cloud of vaporized rock and dust that blocked out sunlight and triggered the extinction of three-quarters of life on the planet, including the dinosaurs.

More recently, a meteor either exploded or streaked over the Podkamennaya Tunguska River, in a remote part of Siberia, in June 1908 – killing wildlife and flattening an estimated 80 million trees across more than 2,000 square kilometers of forest.

Researchers didn’t explore the area and investigate the “Tunguska event” until more than a decade later. Locals reportedly believed it had been a visit from an angry god.

Another unnerving encounter happened recently enough to be captured on video.

A small asteroid about the size of a six-story building entered Earth's atmosphere in February 2013 over Chelyabinsk, Russia, and triggered a blast above the planet's surface that was more powerful than the yield of some nuclear weapons.

It injured more than 1,600 people, mostly due to broken glass. It was also cited by NASA as a “cosmic wake-up call” to do more to detect large asteroids before they strike.

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