1. 16-2 | The Inner Planets

2. The Motion of Planets
The spin of an object in space is called rotation
The amount of time it takes for an object to rotate once is called its period of rotation
The motion of a body as it orbits another body in space is called revolution
The time it takes to revolve around the sun once is called its period of revolution

3. The Inner Planets
The inner planets are more closely spaced than the outer planets
The inner planets are called terrestrial planets because they are small, dense, and rocky

4. Mercury – Closest to the Sun
Less massive; less gravity
1 day = 59 Earth days
1 year = 88 Earth days
Surface temperature = ⁰C
Distance from the Sun = 3.2 light-minutes or AU

5. Venus – Earth’s Twin?
More similar to Earth than any other planet; same size, mass, and density
Rotates in the opposite direction as Earth (clockwise or retrograde)
Rotation is so slow that one day is longer than one year
Atmosphere is the densest of the inner planets: 90x that of Earth’s
Atmosphere is carbon dioxide and acids
Hottest surface temperature: average of 464⁰C

6. Earth – An Oasis in Space
Just the right distance from the Sun
Warm enough to keep water from freezing, cool enough to keep it from boiling away
Water provides means for much of the chemistry that living things depend on

7. Mars – The Red Planet Most studied planet other than Earth
Surface temperature = -123 to 37⁰C
Distance from the Sun = 1.52 AU
Thin atmosphere = less pressure than Earth
Martian day = 34 Earth minutes
Year = 322 days long
Liquid water does not exist, only frozen water in its polar icecaps

8. Mars (Con’t)
Contains largest mountain in our solar system
Olympus Mons
A shield volcano
The size of Arizona
Exploration rover on Mars
Landed in Jan. 2004
Found strong evidence that water once existed on surface of the planet