Why Some Asteroids Burn Up in the Atmosphere While Others Don't

Understanding the behavior of asteroids and comets as they encounter Earth's atmosphere is crucial for a clear picture of cosmic phenomenon. Contrary to common misconception, not all asteroids burn up in the atmosphere. Some do, while others explode in the upper atmosphere without making contact with Earth's surface.

In this article, we will explore the science behind why some asteroids burn up in our atmosphere, the difference between meteoroids and meteors, and the unique characteristics of comets that keep them out of our atmosphere.

Clarifications and Common Misconceptions

The first thing to clarify is that Earth does not pass by asteroids and comets. It is the comets and asteroids that orbit the Sun, and sometimes their orbits bring them close to Earth. When this happens, Earth's gravity can pull some asteroids into its atmosphere, leading to spectacular lights in the sky. It's important to note that comets are not known to enter the Earth's atmosphere, but asteroids can sometimes do so.

Asteroids and Meteoroids: A Closer Look

Asteroids are small rocky objects that orbit the Sun, significantly smaller than planets. A meteoroid is a pebble-sized rock that can be smaller than a grain of sand. Meteoroids originate from asteroids or comets and can burn up upon entering Earth's atmosphere, creating what we call meteors, or shooting stars.

Meteors, the streaks of light in the sky, are actually the trails of light produced by the heated remnants of entering meteoroids. The actual piece of rock is too small and dim to be seen with the naked eye, often only visible at altitudes of about 100 kilometers above Earth's surface.

Speed and Friction: The Culprits

The speed at which an object approaches Earth is key to whether it burns up or not. An object moving in the same direction as Earth's orbit travels at about 10 kilometers per second, while one moving opposite Earth's orbit travels at 70 kilometers per second. Higher speeds result in more heating and hence a greater likelihood of burning up.

Asteroids and meteoroids do not actually burn up due to friction with air. At the high speeds involved, the air in front of the object is compressed, and the compression generates heat. A meteoroid traveling at 70 kilometers per second can reach temperatures as high as 1600°C, which is well above the melting point of iron (1538°C).

Bolides and Their Behavior

Occasionally, larger asteroids heat up in the atmosphere and explode in mid-air, producing a spectacular display known as a "bolide." Bolides are the result of the sudden release of energy from an asteroid as it breaks apart in the atmosphere. Unlike meteors, bolides are typically much larger and cause a louder and more noticeable explosion in the sky.

Comets: A Tangle of Dust and Gas

Comets are very different from asteroids. While asteroids are rocky, comets are composed mainly of ice and dust. As a comet approaches the Sun, ice melts and releases dust and gas, causing it to appear brighter and larger. However, comets typically do not enter Earth's atmosphere because they are much farther away. The nearest comets are millions of kilometers from Earth, making it highly unlikely for them to encounter our atmosphere.

In conclusion, the behavior of asteroids in Earth's atmosphere is a fascinating interplay of speed, friction, and heat. While some meteoroids burn up, others produce bolides, and most do not reach the ground. Comets, on the other hand, are mostly observed from afar, maintaining a safe distance from our atmosphere.