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
                      to be:

   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
ricocheting meteorite.
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
the touch.
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
every year.
•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!
***Peekskill here…
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
Peekskill animation
How can we distinguish meteorites from Earth

                (rocky or carbon-rich)

                   (high density)
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
                            so interesting?

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
  Martian meteorite
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
             Allan Hills
ALH84001                             find      1993    orthopyroxenit    1.90    MWG (JSC), SI
             Bihar, India
Shergotty                            fall      1865    S - basalt        5.00    Calcutta, SI, Vienna
             Katsina, Nigeria                                                    dealers, New Mexico, Berlin, London,
Zagami                               fall      1962    S - basalt        18.00
             Africa                                                              Paris
             Elephant Moraine
EETA79001                            find      1980    S - basalt        7.90    MWG (JSC), SI
             Queen Alexandra
QUE94201                             find      1995    S - basalt        0.012   MWG (JSC)
             Range, Antarctica
             Allan Hills
ALHA77005                            find      1978    S - lherzolite    0.48    MWG (JSC), NIPR (Tokyo)
             Lewis Cliffs
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
             Minas Gerais,
Governador                                             N-
             Brazil                  find      1958                      0.16    Rome, London
Valadares                                              clinopyroxenite
             South America
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,
  micrometeorites or
     space debris?

•over 1/3rd of all impacts were caused by
space debris
•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
                       bigger droplet
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
million years.

•If droplets merge into a single droplet before they cool, lobes
cannot form.

•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
known meteorite?

Willamette meteorite in
Oregon—14.2 tons
 The asteroid belt probably contains millions of
asteroids. Are we in danger of being swarmed by
  these, as pictured in science fiction movies?