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Week 4 topics

Evolutionary hypothesis

Descartes proposed that the solar system formed from a contracting vortex of matter.

Catastrophic hypothesis

Buffon later suggested that a passing comet pulled matter out of the sun to form the planet

Passing star hypothesis

Astronomers replaced the comet with a star from catastrophic (comet) hypothesis

Nebular hypothesis

Laplace's hypothesis required a contracting nebula to leave behind rings that formed each planet

Angular momentum problem

Puzzle of the sun's low angular momentum

Solar nebula theory

Theory proposes that the planets formed in a disk of gas and dust around the protostar that became the sun

Terrestrial planets

Inner four planets, small, rocky, dense

4 terrestrial planet


Jovian planets

Outer planets, large, low density

4 jovian planets



Small, irregular, rocky bodies, are located between the orbits of Mars and Jupiter

Kuiper belt

Small, icy bodies that orbit the sun beyond the orbit of neptune


Icy bodies that pass through the inner solar system along long elliptical orbits. As the ices vaporize and release dust, the comet develops a tail that points approximately away from the sun


Rock in space in space before it plunges into the Earth's atmosphere


Small bits of rock and metal colliding with Earth's atmosphere and bursting into incandescent vapor because of friction with the air about 80 km above the ground. Commonly called "shooting stars".


Specks of dust, grains of sand, or tiny pebbles that survive the passage to Earth's surface.


the age of a rocky body found by radioactive dating based on decay


During the solar nebula converted some of the gas into solid bits of matter


Bits of matter from condensation grow by this process


Accretion bits of matter form billions of these


Planets begin growing by accretion of solid material into this

Gravitational collapse

Once a protoplanet approaches about 15 Earth masses, it can begin growing by this process by pulling gas from the solar nebula

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