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.

Origin of Comets Most comets are found in 2 regions of the solar system: Kuiper belt and Oort cloud. Kuiper belt-doughnut-shaped region that extends beyond Neptune’s orbit to about 100 times Earth’s distance from the sun. Oort cloud-spherical region of comets that surrounds the solar system out to more than 1,000 times the distance between Pluto and the sun.

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 – a few miles in diameter A Comet’s Head Outer layer= Coma (water vapor, CO2, and other gases) Solid inner core= Nucleus (frozen ice, gas and dust )

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

Comet’s Orbit Comets move in an elliptical shaped orbit around the Sun.

Asteroids A small and rocky space object. Most asteroids originate in the asteroid belt. The asteroids orbit between the orbits of Mars and Jupiter.

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.

Asteroid Strike Scientists hypothesize that one or more large asteroids hit Earth 65 million years ago and caused extinction of the dinosaurs. Scientists also hypothesize that the largest mass extinction, 250 million years ago, killing off 90% of all species was also caused by a large asteroid.

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.

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

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What do we do if an NEO (Near Earth Object) is approaching? Unknown… Still being experimented. Scientist are calculating ways to use nuclear energy to divert an incoming object. High energy x-ray pulses produce a shock wave to push the NEO in the opposite direction.