Chapter 29 The Solar System The Planets

Overview of Our Solar System M V E M J S U N P (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto) (My Very Energetic Mother Just Sent Us Nine Pizzas.) All planets and their moons (satellites) orbit the Sun in the same direction. All orbits lie in the same plane except Pluto’s orbit.

Early Ideas Planets slowly change position each night relative to the position of the stars. Geocentric Model – Use to think Earth was the center and sun, stars, & planets orbited us. Planets orbit to the east as viewed from earth, but occasionally move in the opposite direction (RETROGRADE MOTION).

Early Ideas Copernicus suggested that sun is center of solar system (Heliocentric Model) Earth and inner planets, which are closer to sun move faster in orbits and pass up outer planets at certain points in their path making them appear to move backwards.

Early Ideas Kepler’s First Law = Planets orbit the Sun in an ellipse, not a circle. 1 Astronomical Unit (AU) – average distance between the sun and earth. (1.496 x 108 km) Other planets’ distance from sun is compared to that of the earth.

Early Ideas Perihelion – point in elliptical orbit when planet is closest to sun. Aphelion – point in elliptical orbit when planet is farthest from sun.

Early Ideas Galileo first person to use a telescope to observe sky. (Saw 4 largest moons of Jupiter) Newton – studied gravity (attractive force between two bodies that depends on their masses and the distance between the two masses. Also found that each planet orbits a point between it and the sun called the center of mass, which is closest to the heaviest body.

Section 29.2 The Terrestrial Planets Inner four planets Close to size of earth Solid, rocky surfaces Mercury, Venus, Earth, Mars

The Solar System

Mercury No moons 1/3 size of earth. Slow rotation (Its revolution (year) is 1/1/2 of its days!)

Mercury

Mercury No atmosphere Hot daytime 427 degrees Celsius; Cold night –173 degrees Celsius. Largest temperature difference of all the planets. Cratered surface with smooth lava created with lava flows similar to our moon. High density suggests a Nickel-Iron core with molten interior.

Venus No moons Brightest planet in our nighttime sky Covered with thick clouds of sulfuric acid Very hot Rotates slowly One day is 243 Earth days

Venus Clockwise spin (opposite the spin of other planets) (Rises in west & sets in east) Retrograde rotation Sister planet to Earth (most like earth in diameter, mass, density) Atmosphere of carbon dioxide which causes Greenhouse effect! Few impact craters; smooth surface indicates volcanic activity Internal structure probably similar to earth.

Venus

Earth Third rock from the sun Distance from sun allows water to exist as solid, liquid, & gas. Liquid water required for life Atmosphere is 78% nitrogen & 21 % oxygen supports life Mild greenhouse effect Tilted 23 ½ degrees on axis causes seasons Wobbles as it spins (precession) due to gravitational pull of moon and sun.

Earth

Mars Red planet (iron in soil) Smaller & less dense than earth 2 moons (Phobos & Deimos) probably captured asteroids Atmosphere similar to Venus, with lower pressure and density & no greenhouse effect.

Mars Windy; dust storms Southern surface is cratered; smooth northern surface with 4 giant shield volcanoes Dried river & lake beds suggest water once existed on Mars; has some carbon dioxide ice (dry ice) at poles. Probably a solid nickel & iron core.

Mars = The Red Planet

Section 29.3 The Gas Giant Planets Outer planets are gas giants composed of fluids, gases and small solid cores. H, He, C, N, O (all light weight) 15 to 300 x mass of earth 4 – 10 times the earth’s diameter

Section 29.3 The Gas Giant Planets

Jupiter largest planet 11 x larger diameter than earth & 10 x smaller than sun 70% of all planetary matter in solar system banded appearance (flow patterns in atmosphere) 4 major moons + at least 12 smaller ones

Jupiter volcanic moon Io (Europa, Ganymede, Callisto) made of ice & rock H & He atmosphere 10 hour rotation (shortest of any planet) Great Red Spot giant storm on surface Has a ring

Jupiter’s Red Spot is a Storm

Saturn 2nd largest rotates rapidly for its size H & He atmosphere and ammonia clouds Extensive ring system made of rock & ice ( 7 major rings made of smaller ringlets) May have come from an asteroid that collided with planet. 18 moons (Titan is larger than earth’s moon)

Saturn

Uranus Blue planet 18+ moons & 10 rings (dark in color) methane atmosphere reflects blue light (H & He) Rotates almost on its side May have been knocked sideways by an asteroid. Cold

Uranus Tilted on its side.

Neptune Slightly smaller than Uranus Blueish color due to methane atmosphere Great Dark Spot (storm ) similar to Jupiter’s Red Spot disappeared in 1994 8 moons (Triton is largest; retrograde motion ; orbits backwards; has nitrogen geysers) 6 rings made of dust particles

Neptune The dark spot is a storm similar to the one on Jupiter but not a large.

Pluto solid surface, but not classified as terrestrial due to low density & small size. Made of half ice & half rock Smaller than earth’s moon Methane & nitrogen atmosphere

Pluto Pluto’s one moon Charon is shown in the upper left corner.