The Sky is Falling

1. Shoting stars ,or meteors, are bits of interplanetary material falling through Earth’s atmosphere and heated to incandescence. These objects are called meteoroids when hurtling through space, only becoming meteors for the few seconds they streak across the sky and create glowing trails. 
2. Several meteors per hour can usually be seen on any given night. Sometimes the number increases dramatically; these events are termed meteor showers. Some of these meteor showers occur annually or at other regular intervals as Earth passes through the trail of dusty debris left by a comet. Meteor showers are usually named after a star or constellation this close to where the meteors appear in the sky. Perhaps the most famous are the Perseids, which peak around 12 August every year. Every Perseid meteor is a tiny piece of the comet Swift-Tuttle, which swings by the Sun every 133 years. Other meteor showers and their associated comets are the Leonids (Tempel-Tuttle), the Aquarids and Orionids (Halley), and the Taurids (Encke).
3. Most comet dust in meteor showers burns up in the atmosphere before reaching the ground; some dust is captured by high-altitude aircraft and analysed in NASA laboratories. Chunks of rock and metal from asteroids and other planetary bodies that survive their journey through the atmosphere and fall to the ground are called meteorites. Scientists estimate that fortyfour tonnes (forty-four thousand kilograms) of meteorites fall to Earth each day. Most of these meteorites are pebble- to fist-sized, but some are larger than buildings. Early Earth experienced many large meteorite impacts that caused extensive destruction. A very large asteroid impact sixty-five million years ago, which created the three-hundred-kilometre-wide Chicxulub crater on the Yucatan Peninsula, is thought to have contributed to the extinction of about seventy-five percent of marine and land animals on Earth at the time, including the dinosaurs.
4. One of the most intact impact craters is the Barringer Meteorite Crater in the southwestern United States. The crater, which is about one kilometre across, was formed by the impact of a piece of iron-nickel metal approximately fifty metres in diameter. It is only fifty thousand years old and so well preserved that it has been used to study impact processes. Since this feature was recognised as an impact crater in the 1920s, about 170 impact craters have been identified on Earth.
5. Meteorites may resemble Earth rocks, but they usually have a burnt exterior. This fusion crust is formed as the meteorite is melted by friction when it passes through the atmosphere. There are three major types of meteorites: the irons, the stones and the stony-irons. Although the majority of meteorites that fall to Earth are stony, more of the meteorites that are discovered long after they fall are irons; these heavy objects are easier to distinguish from Earth rocks than stony meteorites are.
6. More than fifty thousand meteorites have been found on Earth. Of these, a tiny 0.2 percent come from Mars or the moon. The remaining 99.8 percent come from asteroids. Contrary to popular belief, asteroids and the meteorites that fall to Earth are not pieces of a planet that broke apart, but instead are the original diverse materials from which the planets formed. As a consequence, the study of meteorites tells us much about the earliest conditions and processes during the formation of the solar system: meteorites can indicate the age and composition of solids, the nature of organic matter, the temperatures achieved at the surface and interiors of asteroids, and the degree to which materials were shocked by impacts. In other words, meteorites provide a window into the origins of the solar system, giving us valuable information with which to better understand the history behind the planets we know today. 

Adapted from NASA, ‘Meteors & Meteorites: In Depth’