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Solar system - the sun, all of the planets, & other bodies that travel around it Solar System StarsPlanetsMoons

 Planet - a celestial body that orbits the sun, is round because of its own gravity, & has a clear orbital path

 The features of a planet depends on its distance from the developing sun.  The four inner planets: Mercury, Venus, Earth, & Mars › Were close to the sun › Heat made them lose lighter elements › Made of large amounts of heavy elements (iron & nickel) › Are smaller, rockier, & denser

 The outer planets are Jupiter, Saturn, Uranus, & Neptune. › formed in the colder areas far from the sun › B/C of the cold, they did not lose their lighter elements or their ices › Called Gas Giants › Composed mostly of gases, have low density, & are huge

 Discovered in 1930  known as the ninth planet  very cold (frozen gases & rocks) In 2006, astronomers reclassified Pluto as a dwarf planet.

 When Earth first formed, it was very hot.  In a process called differentiation, denser materials sank to the center, & less dense materials were forced to the outer layers. Layers: › Core (iron & nickel) › Mantle (thick layer of iron- and magnesium- rich rock) › Crust (outermost layer, silica-rich rock)

Outgassing, formed a new atmosphere. › Volcanic eruptions released large amounts of gases  water vapor  carbon dioxide  Nitrogen  Methane  sulfur dioxide  ammonia

 Ozone (0 3 ) › formed from remaining oxygen molecules › collected in atmospheric layer around Earth › shielded Earth’s surface from the harmful ultraviolet radiation of the sun

Organisms that could survive in Earth’s early atmosphere developed. › cyanobacteria & early green plants used carbon dioxide during photosynthesis › produced oxygen as a byproduct › slowly increased the amount of oxygen in the atmosphere

 Over millions of years, rainwater fell to Earth creating freshwater oceans › Rains dissolved some of the rocks on land › carried dissolved solids into the oceans › some of these chemicals combined to form salts

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1. Geocentric  Aristotle suggested an Earth-centered model of the solar system.  Everything revolved around Earth 2. Heliocentric  Copernicus proposed a sun-centered model  planets revolved around the sun in the same direction, but at different speeds & distances from the sun.

 Mercury, Venus, Earth, & Mars › Also called terrestrial planets Terrestrial planets - highly dense planets nearest to the sun › mostly of solid rock and metallic cores › Very few moons  The surfaces of inner planets have bowl-shaped depressions called impact craters › caused by collisions of the planets with other objects in space

 Planet closest to the sun › circles the sun every 88 days › rotates on its axis once every 59 days  Named after messenger of the gods, who moved very quickly.  Heavily cratered & has no atmosphere  Temperatures as high as 427 °C and as low as –173 °C

 Second planet from the sun › Goes around the sun every 225 days › rotates very slowly, only once every 243 days › Brightest thing in the night sky  Venus and Earth are of almost the same size, mass, & density... But › 92 x hotter (melts lead) › 90 x heavier atmosphere › Clouds of sulfuric acid

 Earth is the third planet from the sun. › orbital period = 365 1/4 days › one rotation = 24 hours › one large moon  Geologic records indicate that over the last 250 million years, Earth’s surface has undergone many changes.

Earth’s unique atmosphere & distance from the sun allow water to exist in a liquid state. › Other planets are too close or far away, so that water boils or freezes  Only known planet that has the proper combination of water, temperature, & oxygen to support life (as we know it).

Fourth planet from the sun › orbital period = 687 days › rotates every 24 hours & 37 minutes  The pressure & temperature are too low for water to exist as a liquid, but...  NASA spacecrafts have found evidence that liquid water did exist on Mars’s surface in the past. › features characteristic of erosion by water › ice just below the surface

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 Jupiter, Saturn, Uranus, & Neptune › separated from inner planets by a ring of debris called the asteroid belt Gas giant - planet that has a deep massive atmosphere › larger, but much less dense › did not lose their original gases › have ring systems made of dust & icy debris

 Fifth planet from the sun › largest planet › 300 times that of Earth › orbital period =12 years › fastest rotation (10 hours) › has at least 63 moons (4 are the size of small planets) › several thin rings

 Hydrogen & Helium = 92% of Jupiter  The Great Red Spot is a hurricane-like storm that has been raging for several thousand years.  The Galileo spacecraft measured wind speeds up to 540 km/h. › as high as 30,000 º C

 Sixth planet from the sun › orbital period = 29.5 years › rotates every 10 hours & 30 min › made of hydrogen & helium › has a rocky, iron core › least dense planet in the solar system  Saturn is very cold › average temperature of –176 °C  Saturn has 60 moons › largest moon, Titan, is half the size of Earth.

 Seventh planet from the sun  third-largest planet in the solar system › orbital period = 84 years › at least 27 moons & 12 thin rings › Average temp. =  Uranus’s axis is almost parallel to the plane of its orbit ( turned on it’s side!) › rotates every 17 hours

 Eighth planet › solar system’s strongest winds, which exceed 1,000 km/h › average temp. = is – 225 °C  The Great Dark Spot was a giant storm the size of Earth that appeared & disappeared on Neptune’s surface.

 Now a dwarf planet › made of frozen methane, rock, & ice › average temperature of –235 °C › very thin nitrogen atmosphere › three moons