What Are the Causes of Falling Stars?

Comets

Many meteors come from comets. A comet consists of a ball of rocky rubble and frozen gas. Beyond the solar system -- in the Kuiper Belt and farther out in the Oort Cloud -- icy objects made of frozen gas and rock circle the sun. Occasionally one of these frozen objects is displaced by a passing star or by forces from the Milky Way galaxy, and the frozen object becomes a comet. As it shoots toward the sun, the frozen gas inside heats up, and it releases swaths of rocky rubble. In time, these swaths dissipate, and Earth's gravity regularly captures pieces of the rubble. They enter the Earth's atmosphere as falling stars.

When the solar system formed, it left a band of asteroids between Mars and Jupiter in its wake. The tumbling asteroids collide, creating smaller chips of rocky objects. This band of rocky material -- asteroids and chips -- pool together like a vast lake, but it is a leaky lake. A steady stream of asteroid chips is drawn to Earth by gravity. These chips become falling stars. They are easy to identify because their composition is similar to that of the rocky material found in this belt. Scientists conclude that many meteors originate from this belt.

It takes thousands of years for comet rubble to disperse. When the Earth passes through dense areas of this material, meteor showers are visible in the night sky. The number of visible meteors can rise from a few per hour to hundreds or even thousands per hour. One well-known meteor shower, the Leonids, peaks during mid-November, when the Earth passes through the path of the Tempel-Tuttle comet. An annual event, this shower is especially bright every 33 to 34 years in conjunction with the orbit of Tempel-Tuttle.

Humans have been sending up artificial satellites since Sputnik's launch in 1957. Over time, man-made objects become obsolete, and are abandoned by the people who put them there. Since they are no longer powered, the gravity of the Earth pulls them downward. This space junk breaks up to create impressive displays. Some have historical significance. The abandoned Skylab Space Station created a spectacular swarm of meteors when it returned to Earth in July 1979. Debris from the space station scattered over the Indian Ocean and Western Australia. The pieces returned to Earth with spark showers, fireball effects and whizzing sounds.