Meteors, Meteoroids, and Meteorites

Young Astronomers Blog, Volume 28, Number 17.

Have you ever gone out at night and looked up at the stars? From time to time you might see a streak of light stretch across the sky. Many people call these “shooting stars”. But they are not stars at all. They are meteors – small chunks of dust burning up in the Earth’s atmosphere.

Meteors, meteoroids, and meteorites are three terms associated with “shooting stars” that many people, including me, mix up.

• Meteoroids are dust and small chunks of rock hurtling through space.
• Meteors are meteoroids that enter the Earth’s atmosphere and streak across the sky with a glowing tail.
• Meteorites are meteoroids that hit the ground.

According to NASA’s Solar System Exploration, close to fifty tons of “meteoritic material” falls to Earth daily and most of the meteorites found on the Earth come from asteroids.

Meteorites are classified into three groups.

• Stony are the most common and are made mostly of rock.
• Iron are heavier and are made mostly of metal.
• Stony-Iron are composed of a combination of the two.

Most meteors are as small as a gain of sand, become visible at around 50 to 75 miles up, and burn up in the Earth’s atmosphere. The light given off by a meteor is caused by compression, which heats the air in the meteor’s path. The air then cools and emits the light we see. Meteors lose mass as they “burn up” in the atmosphere through something called ablation.

Although most meteorites are extremely small, there are a few notable exceptions.

• A large asteroid created the Chicxulub crater near the Yucatan Peninsula 65 million years ago and is thought to have wiped out the dinosaurs.
• A 150-foot-wide meteorite impacted what is now Arizona 50,000 years ago and created the Barringer Crater.

Bolides are meteors that explode in a fireball. There are two famous “super bolides”.

• A few hundred-foot-wide meteoroid leveled several tens of million trees near Tunguska, Siberia in 1908.
• A fifty- to sixty-foot-wide meteoroid exploded in the atmosphere above Chelyabinsk, Russia in February 2013.

Meteor Showers are annual events when many meteors can be seen during a single evening. Most meteor showers occur as the Earth passes through the debris field left by a comet (or an asteroid). Meteor showers are named after the constellation from which the meteors appear to radiate and not after the comet. They are best viewed from a dark location on a moonless night. Most peak after midnight and before dawn when the Earth’s night side is facing in the direction of the Earth’s orbit and the direction from which the meteoroids are coming.

The Perseids in August and the Geminids in December are the two best meteor showers of the year. At their peak, you might see one or more meteors per minute.

Mid-August marks the time for the Perseids meteor shower. So, around August 11^th through the 13^th, if it is clear, go out at night (or early in the morning) and look up. If you are lucky you might see some meteors steaking across the night sky.

Oh, and just in case you are wondering, Meteorology is the study of the weather and has nothing to do with meteors. The study of meteors, meteorites, and meteoroids is called Meteoritics.