16-2 | The Inner Planets

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

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

Mercury – Closest to the Sun Less massive; less gravity 1 day = 59 Earth days 1 year = 88 Earth days Surface temperature = 173-427⁰C Distance from the Sun = 3.2 light-minutes or 0.39 AU

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

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

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

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