True or false: We are gaining
weight every day.
Every day, approximately 3000 tons of dusty space material
falls to Earth.
Cosmic debris consists of asteroids, comets, and
•An asteroid is a “minor planet” most commonly
found between the orbits of Mars and Jupiter
•A meteoroid is a small asteroid (less than 100 m in
•A comet is icy rather than rocky and typically 1-
10 km in diameter
Cosmic debris plays no important role in the present-
day workings of the planets or their moons. Why
then do we study them?
Until the 18th century, meteorites were believed
1. Gifts or missiles from the gods…to be worshiped or feared.
2. Rocks from distant volcanoes.
3. Terrestrial rocks swirled up and dropped by powerful hurricanes.
Could meteorite explosions explain the legends of wrathful gods who
could rain fire onto the Earth, as, for example, in the legend of the
destruction of Sodom and Gomorrah?
Rev 16:21 From the sky, huge hailstones of about a hundred pounds
each fell upon men. And they cursed God on account of the plague of
hail, because the plague was so terrible.
True or false: Thomas
Jefferson believed that rocks
falling from the sky reflected
the wrath of the gods.
"It is easier to believe that Yankee
professors would lie than that stones
would fall from heaven."
Where do most meteorites come from?
Where do we look for meteorites?
Most meteorites fall into the oceans.
Most meteorites in museums are discovered in Antarctica.
What can Antarctic
micrometeorites tell us?
Changes in our atmosphere.
What are the odds of getting hit by a
Meteorites have injured at least one human (by a ricochet,
not a direct hit), damaged houses and cars, and killed animals.
Some hits and near-misses
1650 - Monk killed in Milan, Italy (?) He was praying
at the time
1911 - Nahkla (Egypt) meteorite impact kills dog
1938 - Illinois woman hears crash in garage. Finds
meteorite lying on the cushion of her car seat.
1954 - Alabama woman is seriously injured on hip by
1971 - House in Wethersfield, Connecticut is hit by
meteorite. 11 years later another house just a mile
away is also hit.
1991 - Two boys in Noblesville, Indiana hear whistling
and thud. They find lying near sidewalk in a small
crater a meteorite ~2x4 inches. It was slightly warm to
1992 - Michell Knapp's 1980 Chevy Malibu has truck
destroyed in Peekskill, NY. 30-lb meteorite is found on
ground, inches away from gas tank. She is offered
$69,000 for bolide, far more then the car is worth.
Why don’t we see more impacts?
•“Shooting stars” can be seen every night.
•Brick-sized interplanetary stones fall from the sky in various locations
•6 out of 7 events occur over the oceans.
•In 1972, a 1000-ton object skimmed tangentially through Earth's
atmosphere over the Grand Tetons in Wyoming.
•Several houses and a car have been hit in recent decades.
It could happen right now!
True or false: Meteorite damage is not
covered by auto insurance
The Peekskill meteorite, 1992,
turned a Chevy into a celebrity
The car gets its own special exhibit at the American Museum of Natural Hiistory, New York City
How can we distinguish meteorites from Earth
(rocky or carbon-rich)
Most of the meteorites collected on Earth are of the
rocky variety, even though most asteroids are of the
carbon-rich variety. Why is that?
***What makes this rock
1. isotope ratios consistent with other martian rocks
2. carbonate globules that suggest water
3. deposits of minerals that have in some cases
been produced by bacteria
4. structures that resemble bacterial fossils on Earth
5. rock compounds that often have biological origins
suggests possibility of
life on Mars
The 12 Martian rocks
Martian Meteorite Summary
Compiled by Marilyn Lindstrom, PhD, NASA, Johnson Space Center (October 1996)
Name Find Location find/fall Year Classification Curatorial Location
ALH84001 find 1993 orthopyroxenit 1.90 MWG (JSC), SI
Shergotty fall 1865 S - basalt 5.00 Calcutta, SI, Vienna
Katsina, Nigeria dealers, New Mexico, Berlin, London,
Zagami fall 1962 S - basalt 18.00
EETA79001 find 1980 S - basalt 7.90 MWG (JSC), SI
QUE94201 find 1995 S - basalt 0.012 MWG (JSC)
ALHA77005 find 1978 S - lherzolite 0.48 MWG (JSC), NIPR (Tokyo)
LEW88516 find 1991 S - lherzolite 0.013 MWG (JSC)
Y793605 find 1995 S - lherzolite 0.018 NIPR (Tokyo)
Alexandria, Egypt N- Cairo, London, SI, Berlin, Vienna, Paris,
Nakhla fall 1911 10.00
Africa clinopyroxenite dealers
Indiana, USA N-
Lafayette find 1931 0.80 SI, Chicago
North America clinopyroxenite
Brazil find 1958 0.16 Rome, London
Chassigny France fall 1815 C - dunite 4.00 Paris, Vienna, London
How big are most meteorites?
Most are less than one millimeter across and
are called micrometeorites.
Which causes more
damage to satellites,
•over 1/3rd of all impacts were caused by
•micrometeorites cause only 1/10th
Which one is the micrometeorite?
pollen grain coccolith
micrometeorite grain of sand
Which of these hypotheses most likely
explains the structure of this micrometeorite?
Hypothesis #1: Two or more droplets
Hypothesis #2: A single droplet passes
through the atmosphere more than once.
Hypothesis #3: Two or more droplets from a
single micrometeorite are torn off and
Hypothesis #1: Several droplets collide and merge to a form a
Hypothesis #2: Single micrometeorite reentered the
Earth’s atmosphere several times
Hypothesis #3: Fragments from single
micrometeorite recombine irregularly
Factors to consider:
•Most cosmic dust particles will collide roughly once every 10
•If droplets merge into a single droplet before they cool, lobes
•Two liquid droplets will merge into a single droplet after
0.001 seconds, but a droplet takes 0.3 seconds to cool and
•A particle hitting the atmosphere at a high enough speed, and
low enough angle, could pass back into space; this would
allow it to heat up at two different temperatures and different
patterns of cooling would be seen.
What’s wrong with this picture?
What is the largest
Willamette meteorite in
The asteroid belt probably contains millions of
asteroids. Are we in danger of being swarmed by
these, as pictured in science fiction movies?