Chapter 29, section 1 & 2
Two solar system models →
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Models of the Solar System and the Inner planets
1) geocentric model (Earth-centered model)- the sun, the stars, and
the planets all revolve around Earth
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Believed for almost 2,000 years because the church supported it
2) heliocentric model (Sun-centered model)- Earth and other planets
all orbit around the sun)
 Correct and current model of the solar system
Orbits of planets →
Planets orbit around the sun in an elliptical (oval) shape. Sometimes
planets are closer to the sun, and sometimes they are further away
The inner planets →
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Mercury, Venus, Earth, and Mars
Also called the terrestrial planets and/or the rocky planets
Characteristics of the inner
planets →
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Made mostly of rock and metal
Are solid
Have high densities
Have no rings
Have few to no moons
Rotate (spin) slowly
Mercury →
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Smallest of all the planets
Rotates once every 59 days
Has the greatest temperature range (high 427°C, low -173°C)
Has a very thin atmosphere and so it is covered with craters made
by asteroids and meteoroids
Venus →
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Called ‘Earth’s twin’ - similar in size, mass, and composition
Rotates, in the opposite direction of other planets, every 225 days
Has an average temperature of 464°C (hot enough to melt lead!)
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Because it is close to the sun and has a dense atmosphere
Has a thick atmosphere made of mostly of carbon dioxide (CO2)
that is thick enough to crush a human. The thick atmosphere acts
like a blanket that covers the planet, & prevents heat from leaving
Earth →
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Mars →
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Third planet from the sun
The only planet with life and liquid water
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Geologically active- which creates earthquakes and volcanoes
Has an atmosphere of ~75% nitrogen and ~25% oxygen
Has a magnetic field which protects us from solar wind
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Has two moons
Evidence from erosion suggests that the planet was once warmer
and wetter
Only planet that a unmanned spacecraft has landed on
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