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Chapter 13
Cosmic Samples and the Origin of
the Solar System
What are some of the
general patterns in the
solar system?
What do these patterns
tell us about the how
the solar system
formed?
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13.1 Meteors
• When comets approach the Sun, they are heated and
material sprays off of them.
• This material remains in orbit around the Sun.
• If the Earth passes through a cloud of this material,
some of it is caught in the atmosphere where it is
heated, glows, and produces a meteor or shooting
star. (A shooting star has no connection to a real
star.)
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13.1.2 Meteor Showers
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13.2 Meteorites: Stones from Heaven
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Meteorites
• A meteorite is any fragment that survives its passage
through the atmosphere and reaches the ground.
• It wasn’t realized that meteorites are extraterrestrial
(not from Earth) until the 18th century.
• Meteorites are found in two ways:
– Someone tracking a meteor to the ground.
– Someone finding an unusual looking rock
– Antarctica is now a major source of meteorites.
• The oldest meteorites are about 4.5 billion years old.
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13.3 Formation of the Solar System
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Observational Constraints
• The information we’ve learned about the planets,
moons, rings, asteroids, comets should be explained
by any theory for the formation of the solar system.
• We have three types of constraints:
– Motional
– Chemical, and
– Age
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Observational Constraints
1. Motional
•
•
•
•
All the planets revolve around the Sun in the same direction and
in approximately the same plane as the Sun rotates.
Most planets rotate in the same sense that they revolve.
Most of the satellites rotate and revolve in the same sense as
well.
There are exceptions that the theory must handle, like Venus’s
retrograde rotation.
2. Chemical
•
•
•
The jovians are similar in composition to the Sun and stars.
Other planets are lacking in hydrogen and helium.
The inner planets are metal rich, then farther out are rocky
objects, and farther still are icy objects.
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Observational Constraints (cont’d)
•
•
Temperature progression from inner to outer planets
How to explain the presence of water on Earth and
Mars
3. Age
•
•
•
•
•
Earth samples are up to 3.8 billion years old
Lunar samples are up to 4.4 billion years old
Primitive meteorites are 4.5 billion years old
Indicates that planets must have cooled rapidly
Little unaltered material left from before the formation
of the solar system.
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13.3.2 The Solar Nebula
• The hypothesis that the solar system formed 4.5
billion years ago from a rotating cloud of hot
material called the solar nebula consistent with the
constraints.
• The composition of the nebula is similar to the Sun’s
composition.
• As the cloud collapsed, it heated, destroying most of
the evidence of its original state.
• As material falls inward, the rotation becomes faster
(angular momentum) and results in a disk shape.
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Forming the Solar System
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13.3.5 Further Evolution
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Elevation Differences
• Mountains come from a number of sources
• On the Moon and Mercury, the mountains are ejecta
from large impacts.
• The large mountains on Mars are volcanos.
• On Earth, the largest mountains result from
compression and uplift of crustal plates.
• On Venus, the larges mountains result from uplift by
subsurface magma.
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Elevation Differences
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Mountains
• Why does Mars have the highest mountain in the
solar system?
1. Mars doesn’t have plate tectonics that can impede large
volcanos. (There are multiple Hawaiian islands because
the Pacific plate is moving over the hot spot beneath.
2. Mars has lower surface gravity than Earth or Venus.
Underlying material can more easily support the weight
of the mountain above. (The mountain “weighs” less.)
3. Mars has a thin atmosphere and little erosion to reduce
the height over millions of years.
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Atmospheres
• Atmospheres are a combination of gas that escaped
from a planet’s interior, and impacts of gascontaining objects (icy comets).
• It is likely that all the terrestrial planets had similar
atmospheres.
– Mercury and the Moon: too small to retain their
atmospheres.
– Venus: runaway greenhouse effect
– Mars: runaway refrigerator effect
– Earth: lucky?
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Conclusion
• There’s still much to learn about the origin and
evolution of the solar system.
• Space probes continue to add to our understanding.
• In the last 10 years we found more than 100 planets
orbiting other stars.
– Perhaps studies of these distant planetary systems will
yield more clues about our own.
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