Asteroids, Comets and Meteors

Main objectives of this unit:• Compare and contrast asteroids, comets and

meteors.• Distinguish between meteroids, meteors, and

meteorites.• Cite the likelihood of being killed by an asteroid,

comet or meteorite impact.• Describe the anatomy of a crater.• Calculate the energy released when an asteroid,

comet or meteorite impacts the earth based on the size of the body.

• Explain why there are not many visible craters on Earth.

Asteroids

• Asteroids are large rocks in space. Most are located between the orbits of Mars and Jupiter.

Asteroids

• It is theorized that the large gravitational attraction of Jupiter caused the asteroid belt by disturbing the formation of a planet at that location.

• Asteroids range from tiny in size to the largest known as Ceres which is 950 km in diameter.

Comets

• Comets are balls of ice and dust.• Most comets originate in the Kuiper belt or Oort

cloud that surrounds our solar system.• Comets have a highly elliptical orbit around the

sun.

Halley’s comet

The tail of a comet always faces away from the sun. The solar wind

blows it away from the sun.

Comets are made up of a coma which contains the solid nucleus and a tail of dust and gas.

The Head and ComaThe nucleus is a few kilometers across and is surrounded by a diffuse, bright region called the coma that may be a

million kilometers in diameter; the coma is formed from gas and dust ejected

from the nucleus as it is heated by the Sun.

The coma is bright both because it reflects sunlight and because its gases

are excited by sunlight and emit electromagnetic radiation.

The TailThe tails of bright comets can be 150 million kilometers (1 A.U.) in length,

making them the "largest" objects in the Solar System. However, the tail is

composed of gas and dust emitted from the nucleus and is very diffuse. The

vacuum in the tail is much better than any vacuum we can produce on Earth. 

Common comets

Pluto? Shoemaker-Levy

Hyakutake

Hale-Bob

Meteors

• Meteoroids are rocks in space.

• Meteors refer to the tail of light produced when a meteoroid enters the atmosphere.

• Meteorites are the rocks that survive the trip through the atmosphere and hit the earth.

Meteors

• Meteors can range from many kilograms to specks of dust.

• The light they produce when they enter the atmosphere is due to friction.

What do you think the chances are of being killed by one of these

objects hitting the earth?

1938 - a small meteorite crashed through the roof of a garage in Illinois

1954 - A 5kg meteorite fell through the roof of a house in Alabama.

1992 - A small meteorite demolished a car near New York City.2003 - A 20 kg meteorite crashed through a 2 story house in uptown New

Orleans2003 - A shower of meteorites destroys several houses and injures 20

people in India

 

                                                                       

                                                             

Cause Odds

Motor vehicle Accident 1 in 100

Murder 1 in 300

Fire 1 in 800

Firearms accident 1 in 2,500

Electrocution 1 in 5,000

Asteroid or Comet impact

1 in 20,000

Airplane crash 1 in 20,000

Flood 1 in 30,000

Tornado 1 in 60,000

Venomous bite or sting 1 in 100,000

Botulism poisoning 1 in 3,000,000

Odds of winning the lottery

1 in 7,900,000

Odds of dying in the U.S.

How do we find asteroids?

Most of the objects in the sky are stars and are very far away. Therefore they move more slowly across the sky than something closer like an asteroid. We look for objects that are moving more quickly than the background stars.

Major extinction events occurred at •the end of the Tertiary Period, 1.6 million years (m.y.) ago.

•the end of the Cretaceous Period, marking the boundary between the Cretaceous and Tertiary periods 65 m.y. ago. (Geologists use the letter K to stand for Cretaceous Period and the letter T for the Tertiary Period. Thus this boundary is commonly called the K-T boundary).

•the end of the Triassic, 208 m.y. ago.

•the end of the Permian, 245 m.y. ago (estimated that over 96% of the species alive at the time became extinct).

•the end of the Devonian, 360 m.y. ago

•the end of Ordovician, 438 m.y. ago

•the end of the Cambrian period, 505 m.y. ago

                                              

Anatomy of an impact

Low angle impacts• When an impact occurs at a low angle, the

crater becomes elongated.• The crater produced is oval rather than

circular.

Direct impact

Low Angle Impact

Newer craters form on top of older craters

Why don’t we see craters on earth?

Earth craters

Meteor Crater in Arizona

Yucatan Crater

Manicouagan Impact Crater Northern Canada

Landsat image of the Kebira Crater in the Great Sahara Desert of Egypt at the border with Libya.

Known earth impacts

• Trees suggest that the Earth has gone through major climate change around the years of 1628 B.C., 1159 B.C., 207 B.C. and 540 A.D. All coincide with possible references to comets in myth and legend.

• The fear of fire-breathing dragons may have been inspired by comets.

Interesting Facts

Effects

• A body 200 yd to 1 mile in diameter would blast a crater up to 10 miles wide resulting in large-scale famine and economic depression. It would also cause a tsunami that would flood all land 200 ft above sea level.

• A body 1- 10 miles in diameter would create a crater 100 miles across. The resulting dust cloud would cause “nuclear winter”.

• A body greater than 10 miles across would mean the end of most life on the planet.