In the image pictured here, the dots stand for the various objects that populate the inner solar system…comets, asteroids, and the like. The orange dots are the larger global killers. The blue dots are smaller objects that would only cause local devastation. The Earth’s orbit is pictured in green.
As many of you already know, on Friday February 15, 2013 a meteor blasted into the Earth’s atmosphere and broke apart over Russia, releasing nearly 500 kilotons of energy. The energy released by this explosion is equal to about 30 Hiroshima bombs. The shockwave created by the event injured more than 1,000 people and blew out the windows in more than 100,000 homes (note: this figure does not include schools, hospitals, or office buildings).
On Thursday February 21, scientists confirmed that fragments of the meteor had been recovered. Although the initial size of the object is estimated at about 55 feet (17 meters), and nearly 10,000 tons, the most of the fragments were smaller than 7 millimeters (though some were larger). Fortunately, the meteor's the collisions with the atmosphere (coupled with its fiery dive to Earth) caused it to fragment and break apart into tiny pieces. None the less, this meteor was a fairly sizable object. One seemingly reasonable question I’ve often heard repeated is, “why didn’t we see it coming?”
Unfortunately, technology has its limitations. If an object is beneath a certain size, we simply can’t detect it. No warning, no foreknowledge, no preparation. Just a sudden realization the moment that it begins to streak across our sky. However, if you’ve been keeping up with the news, you’ll know that such collisions are relatively rare. Typically, impact events of this magnitude (like the one in Russia) only occur once a century. If we can’t see or predict these events, it helps to know that at least such occurrences are relatively rare. It’s comforting. At least, it’s comforting until you start doing some research on Potentially Hazardous Asteroids.
Potentially Hazardous Asteroids (PHAs) are asteroids that have the closest orbits to the Earth, coming within five million miles/eight million kilometers. PHAs are big enough that, if one of them were to blast into our atmosphere, it would survive the searing trip to the Earth’s surface (as opposed to breaking up and decomposing in the atmosphere, like a smaller object would). And it would cause damage on a regional, or potentially even a global, scale. So far, NASA’s NEOWISE survey has uncovered more than 4,700 PHAs looming in the cosmos. They are pictured in orange in the image. This may seem scary (and it is, a bit); however, Earth's orbit is fairly large, so these objects pass through the Earth's orbital plane when the planet is far, far away.
Pictured in blue you see some of the 20,000 Near-Earth Objects (NEOs) that are larger than 330 feet (100 meters). An impact with objects the size of the NEOs wouldn’t cause a global catastrophe. However, if it hits in the wrong area, the death toll would be horrifying. A major problem with these objects is that scientists estimate that only 20 to 30 percent of the PHAs thought to exist have actually been discovered.
Now, I’m not saying you should fear for your lives. This doesn’t mean that a global killer is going to come rushing in and destroy us all. Rather, it highlights how we need to be aware of our precarious position. Humanity, the Earth, is a fragile thing. And it is worth protecting if we can. Which is precisely why we need NASA and other space agencies. It’s why we must continue to fund science and science education. As the saying goes, knowledge is power.