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Close encounters of many kinds
Chapter 6: Origin of small bodies in the Solar System and what can they do to us…
The origin of meteors and meteorites
• Meteorites are survivors from the time of the solar system formation
• Most of meteors and certainly meteor showers are a fragile cometary material that
never reaches the ground
• Meteorites are structurally much stronger and appear to be pieces of asteroids. In fact,
studies of their orbits trace them back to the asteroid belt
The origin of asteroids
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Old theories proposed a catastrophic origin of asteroids, such as an explosion of the original planet
Our current understanding is that asteroids originate from the material that failed to form a planet at
about 2.8 AU from the sun
The planet could not form, because of a gravitational influence of Jupiter
Most asteroids are fragments produced in collisions over the ~4.6 billion years of their existence
The origin of comets
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Most comets have highly elliptical orbits with periods longer than 200 years, but there is also a family
of comets with much shorter periods
Long-period comets originate in a spherical cloud of icy bodies extending from 10,000 to 100,000 AU
away from the sun and called the Oort cloud
Some short-period comets can come from the Oort cloud and have their orbits altered by Jupiter, but
most of them are thought to belong to the Kuiper belt located just beyond the orbit of Neptune
Impacts on Earth
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Collisions of planets with interplanetary space debris are inevitable
Small meteorite impacts are very common, but encounters with large bodies (comets, asteroids) are
thought to occur millions of years apart
Evidence for such impacts have been found at many locations on Earth
For example, a 150 km diameter crater at Yucatán peninsula has been caused by the impact of an 10-14
km object 65 million years ago, at the time of extinction of dinosaurs and many other species
Fire from the sky (movie)