Comets, Asteroids, and Meteors Section 5: Comets, Asteroids, and Meteors

Comets The word "comet" comes from the Greek word for "hair.” Our ancestors thought comets were stars with what looked like flowing hair trailing behind.

Comets: “Dirty Snowballs” Comets are loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses.

Structure of a Comet Outer layer= Coma Solid inner core= Nucleus A Comet’s Head Outer layer= Coma Solid inner core= Nucleus

Comet’s Tail As a comet approaches the sun and heats up, some of its gas and dust stream outward, forming a tail. Most comets have 2 tails: gas (ion), tail dust tail Tails point away from the sun because of the force of the solar wind. A comet’s tail can be more than 100 million kilometers long.

Comet’s Tail

Famous Comets Comet Halley is perhaps the most famous comet in history. Each time this comet's orbit approaches the Sun, its 15- km (9-mile) nucleus sheds about 7 yards of ice and rock into space. This debris forms an orbiting trail that, when falling to Earth, is called the Orionids meteor shower. Halley’s comet reappears every 76 years. Its next appearance is in 2061.

Comet Hale-Bopp July 23, 1995- an unusually large and bright comet was seen outside of Jupiter's orbit by Alan Hale of New Mexico and Thomas Bopp of Arizona. Exceptionally large size. It was visible even through bright city skies, and may have been the most viewed comet in recorded history. It will not appear again for another 2,400 years.

Comet Possibilities… was launched in December 2004 and encountered comet http://science.discovery.com/video- topics/space-videos/comets.htm

Asteroids A small and rocky space object. Most asteroids are found in the asteroid belt. The asteroid belt is located between the orbits of Mars and Jupiter. http://www.cnn.com/2013/02/05/world/space -asteroid/index.html

How many asteroids are there? There are about 40,000 known asteroids that are over 0.5 miles (1 km) in diameter in the asteroid belt About 3,000 asteroids have been cataloged. There are many smaller asteroids (100,000). Asteroids are made of metals, silicate, iron, nickel, and carbon. The first one discovered (and the biggest) is named Ceres; it was discovered in 1801. Asteroids range in size from tiny pebbles to about 578 miles (930 kilometers) in diameter (Ceres).

ASTEROIDS BECOMING MOONS Asteroids can be pulled out of their solar orbit by the gravitational pull of a planet. They would then orbit that planet instead of orbiting the Sun. Astronomers theorize that the two moons of Mars, Phobos and Deimos, are captured asteroids.

Meteoroids Meteoroid-chunk of rock or dust in space. Meteoroids come from comets or asteroids.

Meteor When a meteoroid enters Earth’s atmosphere, friction with the air creates heat and produces a streak of light that you can see in the sky. A meteor is a meteoroid that enters Earth’s atmosphere and burns up. Two famous meteor showers are the Leonids and the Perseids.

Meteorites Meteoroids that pass through the atmosphere and hit Earth’s surface are called meteorites. Classified by composition: stony, iron ,or stony-iron.