Chapter 25 Meteorites, Asteroids, and Comets Astronomy Name: Date: Pd



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Chapter 25 – Meteorites, Asteroids, and Comets

Astronomy Name: Date: Pd:


I. Meteorites

a) Below, distinguish between a meteoroid, meteor, and meteorite. Include a sketch.


b) Sizes from microscopic to a few ________________

c) About __________ meteorites, large enough to produce visible impacts, strike the earth every _______________

d) Statistically, ______________ meteorite is expected to strike a building somewhere on Earth every ______________ months.

e) Typically impact onto the atmosphere with _____________________ (about 30 x faster than a rifle bullet)

II. Finding Meteorites



  1. Most meteorites are ______________ and do not produce significant craters.

  2. Good place to find meteorites: _________________________

  3. In the space below, distinguish between meteorite “falls” and “finds”

III. Analysis of Meteorites



  1. 3 broad categories

  1. Iron: very _______________ for their size and have a dark, irregular surface

  2. Stony: tend to have a fusion crust caused by _________________ in Earth’s atmosphere

  3. Stony-Iron: A mix of both

IV. What does a Meteorite look like?

  1. The greatest amount of Falls are __________________ with ______________ percent

  2. The Finds are somewhat split between _____________ Iron and ______________ Stony

  3. Selection bias: __________________ meteorites are easy to recognize as meteorites (heavy, dense lumps of iron-nickel _______________) – thus, more likely to be found and collected

V. Meteor Showers

a) Most meteors appear in showers, peaking periodically at specific dates of the year.

b) When is the next meteor shower? ____________________

c) Tracking the tracks of meteors in a shower backward, they appear to come from a common origin, the _____________________.



VI. Meteoroid Orbits

  1. Meteoroids contributing to a meteor shower are __________________ particles, orbiting in the path of a __________________.

  2. Spread out all along the orbit of the _________________

  3. Comet may still exist or have been ______________________

  4. Only a few ______________________ meteors are not associated with comet orbits

VII. The Origins of Meteorites

  1. Probably formed in the solar nebula about _________________ billion years ago

  2. Almost certainly not from __________________ (in contrast to meteors in meteor showers!)

  3. Probably fragments of stony-iron _____________________________

  4. Origins of Meteorites stages

  1. Planetesimals cool and _________________________

  2. Collisions eject material from different depths with different _______________________ and temperatures

  3. Meteorites can not have been broken up from planetesimals very long ago, so remains of planetesimals should still exist as ______________________

VIII. The Asteroid Belt

  1. Small, irregular objects mostly in the apparent gap between the orbits of ________________ and Jupiter

  2. Thousands of asteroids with accurately determined _________________ known today

XII. Comets: Two Types of Tails

  1. Gas Tail – Ionized gas pushed away from the comet by the ______________________________. Pointing straight away from the ________________

  2. Dust Tail – dust set free from vaporizing _____________ in the comet; carried away from the comet by the sun’s _____________________ pressure. Lagging behind the comet along its trajectory

XIII. The Geology of Comet Nuclei

  1. Comet nuclei contain ices of _________________, carbon dioxide, ______________________, ammonia, etc: Materials that should have condensed from the _____________________ solar nebula

  2. Those compounds _______________________ (transition from solid directly gas phase) as comets approach the _______________

  3. Dust ejected along with gases often forms ______________________ emanating from active regions on the comet’s surface

  4. Not solid ______________ balls, but fluffy material with significant amounts of empty __________________.

  5. Densities of comet nuclei: __________________________________

  6. Comet dust material can be collected by spacecraft above Earth’s atmosphere

XIV. Sun-Grazing Comets

  1. Some comets come very close to the ________________. These are called “Sun-grazing comets”.

  2. Most of them evaporate and/or get disrupted by the sun’s ___________________ forces

XV. The Origin and History of Comets

  1. Comets are believed to originate in the _________________ cloud: a spherical cloud of several trillion icy bodies about ______________________________ from the sun

  2. Gravitational influence of occasional passing _____________________ may perturb some orbits and draw them toward the inner solar system

  3. Interactions with planets may perturb orbits further, capturing comets in _________________ period orbits

XVI. The Kuiper Belt

  1. Second source of small, icy bodies in the outer solar system: Kuiper Belt at ______________ from the sun

  2. Few Kuiper belt objects could be observed directly by ______________________________________

  3. Pluto and __________________________ are probably captured Kuiper belt objects

XVII. Impacts on Earth



  1. Over _________________ impact craters found on Earth

  2. Famous example: __________________ Crater near Flagstaff, AZ: Formed about 50,000 years ago by a meteorite of about __________________ diameter

  3. Barringer Crater: about ____________ diameter and _____________ deep

  4. Much larger impact features exist on Earth:

  1. Impact of a large body formed a crater about ___________________________ in diameter in the Yucatan peninsula about 65 million years ago – the ________________________ crater

  2. Drastic influence on climate on Earth; possibly responsible for the extinction of ____________________________

  1. The Tunguska Event

  1. The Tunguska event in _____________________ in 1908 destroyed an area the size of a large city!

  2. Explosion of a large object, probably an ________________________ asteroid of 30 m in diameter a few km above the ground

  3. Energy release comparable to a ___________ megaton nuclear weapon!

XVIII. Big Impacts

a) In 1992, Comet Shoemaker-Levy 9 passed very closely to ____________________ and was disrupted by tidal forces

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