Asteroids have captured the public imagination in recent years, thanks in part to Hollywood’s portrayal of their destructive potential. Headlines warning of “city-killer” and “planet-killer” asteroids have become commonplace. But what is the real threat posed by these celestial objects? How many asteroids actually hit the Earth, and how many of them pass dangerously close to our planet?
To understand the threat, it is necessary to turn to statistics. According to NASA, in orbit around the Sun orbits more than half a billion asteroids with a diameter of more than four meters. These asteroids move through our solar system at a speed of up to 30 kilometers per second, which is similar to the speed of the Earth.
Asteroid Impact: Small and Large
It is important to note that there are many more small asteroids than large asteroids. While small asteroids can cause some damage when they collide, their impact is relatively minor compared to the destruction that large asteroids cause. The famous asteroid impact that wiped out the dinosaurs 65 million years ago is a vivid reminder of the destructive power of these celestial objects.
When a small asteroid or meteoroid enters Earth’s atmosphere, it creates a spectacular fireball similar to a shooting star or meteor. Most of these objects burn up in the atmosphere, and only a few surviving fragments reach the earth and are called meteorites.
Frequency of asteroid impacts
So how often do asteroids collide with the Earth? Consider the case of four-meter asteroids. On average, one four-meter asteroid crosses the Earth’s surface every year. If we double the surface area, we can expect to see two such asteroids within 2600 km of the Earth’s surface per year.
As the surface area is further increased, the number of approaches also increases. Recent convergence data are consistent with this estimate. While a few thousand kilometers may seem like a significant distance, it is important to note that most asteroids reported in the media pass at much greater distances.
Experts emphasize the importance of understanding the true risks associated with asteroids. Dr. Alan Harris, a planetary scientist, states, “The threat posed by asteroids is real, but it is important to separate fact from fiction. While large asteroids can have catastrophic consequences, most small asteroids pose minimal danger.”
Historical context also sheds light on the rarity of catastrophic asteroid impacts. The event that wiped out the dinosaurs was a once-in-a-lifetime event, and such large collisions are extremely rare.
