Meteor seenOver Des Moines,Iowa

The LoenidMeteor Shower

The LoenidMeteor Shower

Meteoroids, Meteors, and Meteorites

• Meteoroid refers to the small body in space• Meteor refers to the body once it begins to vaporize in the Earth’s atmosphere• Meteorite refers to the body if it survives to strike the ground

Meteor breaking upover Altoona, PA, 1992

The view from ameteoroid, 10 minutesbefore impacting earth

Why Meteor Showers Occur

Meteor Showers

• Too small to be seen with even the best telescopes.• We see them only when they enter Earth’s atmosphere• They move at about 30 times faster than a bullet from a rifle

Meteor Showers

• Meteors are visible on any clear night, but major meteor showers include:

- Perseid (August)- Leonid (November)- Geminid (December)

• During a shower, the meteors all appear to come from a single point in the sky called the radiant.

Stony meteorite, collected inArizona in April, 2001

Iron meteorite

Stony-Iron meteorite

Meteorites

• Meteorites can be either iron, stony, or stony-iron• Iron meteorites are shiny metal• Stony meteorites are high in carbon content and are the most common• Stony-iron meteorites are the rarest

Asteroid

Ida Dactyl

• Image from Galileo, 8/28/93

• 10,500 miles away

Asteroid Locations

• Asteroids originate in two places:1) The Main Belt, between

Mars and Jupiter2) The Trojan regions, along

the orbital path of Jupiter

AsteroidLocations

Asteroid Belt

Asteroid Belt

Near-Earth Asteroid’s Orbit

Near-Earth Asteroids

Near-Earth Asteroids (Apollo Objects)

• Objects with orbits that cross Earth’s orbit• About 1/3 will eventually be thrown into

Sun• Few will be thrown out of the Solar System• Most will eventually strike a planet—maybe Earth!

Near-Earth Asteroids (Apollo Objects)

• Earth is hit once every 250,000 years, on average• These objects depart from their original

positions in the Asteroid Belt due to collisions there.• A 2km-wide object could hit Earth with the power of a 100,000 megaton bomb, and create a crater 20 km across.

Near-Earth AsteroidsTrafficJam

Sizes of Near-Earth Asteroids

A Comet

Halley’s Comet, March 1986

Comet West, 1975

Parts of a Comet

Dust Tail

Nucleus

Coma

Gas Tail

Comets

• Nucleus can be 10 to 100 km in diameter• Coma can be over 1,000,000 km in diameter—bigger than the Sun!• The tail can be several billion km long• Comets are made water ice, other ice, and rocky material

Comet Hale-Bopp, April 1997

Comet Hale-Bopp, April 1997

Comets

• Originate in the Oort Cloud, a sphere-shaped cloud of ice bodies that surrounds the solar system• Oort Cloud is 10,000 to 100,000 AU from

the Sun• Nearby stars may affect a comet’s orbit,

sending it toward the center of the Solar System

Comets may leave the Oort cloud…

Comets

• The Kuiper Belt also may contain Comets.• The Kuiper Belt is full of small, icy bodies

beyond the planet Neptune

Comets

• Comets that come closer to the Sun (and Earth!) do not last very long.

• Each time a comet approaches the Sun, it sheds ice and dust due to warmth

• A comet such as this may only last 100 to 1,000 orbits around the Sun.

Barringer Meteor Crater, Arizona50,000 years old

200 m deep

What might an impact look like?

200 million year-old craterQuebec, Canada

Impacts on Earth

The effects of an impact depend on:• The size of the impacting body• The speed of the impacting body• The location of the impact• The angle of the impact

A major impact on Earth:

• All organisms near site of impact die instantly due to initial shock• Same overall effects regardless of land or

sea impact• Sea impact would create tidal waves thousands of feet high that would go half way around globe

A major impact on Earth:

• Atmosphere would fill with pulverized rock ejected from ground

• Heat would trigger massive forest fires everywhere• Sunlight blocked, so reduced photosynthesis results in death of plants and animals far from impact site