Chapter 19: The Solar System

Chapter 19: The Solar System Physical Science Doerfler 19.1 Sun, Earth, and Moon Key Ideas: Why does the night sky look the way it does from Earth? What objects make up the solar system? How does the moon affect Earth? Planet Solar system Satellite Phase Eclipse Key Terms 19.1 Bellringer Earth moves around the sun, and the moon moves around Earth. What force keeps these bodies in their paths? Gravity Why it Ma@ers Studying the solar system and its various planets can help us understand our own planet better The View from Earth From now to six months from now, the stars that you see will be different Some star groups move across the sky in just a few hours The positions of objects in the sky change over time because Earth, and everything else in the universe, is constantly moving Planet celestial body that orbits the sun, is round because of its own gravity, and has cleared the area around its orbital path 1

Sun is Closest Star to Earth Took thousand of years to realize sun is a star Our atmosphere scatters sunlight, making it too bright to see the other stars Sun is average star: o Not particularly hot or cool o Average size Diameter is 1.4 million kilometers (nearly 870,000 mi) Sun s mass is about 330,000 times that of Earth s Nature Uses Sun to Set Daily Cycles Sun is major external source of heat and light for Earth Many patterns of animal and human life, such as rising in the morning, eating meals at certain times, and sleeping at night, follow the sun s cycles o Called circadian rhythms The progression of each year has growing seasons of plants o Tulips are sensitive to light; open during day and close at night Sun s energy is also cause of weather patterns and ocean currents What s in the Night Sky? What may seem like a jumbled mass of stars can actually be put together to form constellations o Groups of stars organized in a recognizable pattern These are the same patterns that ancient Greek philosophers looked at By watching the night sky for many years, ancient Greeks calculated that stars more distant than planets o Telescope invented thousand years later o Discovered two more planets: Neptune and Uranus o Several other large celestial bodies: Ceres and Pluto A Family of Planets Solar system has objects and own set of rules The solar system is the sun and all of the objects that orbit it Sun makes up nearly 99% of mass of our solar system Eight planets and their moons make up the remaining 1% Solar system also contains dwarf planets, asteroids, comets, dust, and gas Gravity holds the Solar System Together RECALL every object in solar system pulls on every other object Force of gravity depends on.what??????? o Their masses and distance between them The sun exerts the largest force in the solar system because..? Gravity also keeps moons orbiting around planets Jupiter has gravitational force on use but we don t notice it..why? Eight Planets Orbit the Sun Planets can be seen because their surface or atmosphere reflect sunlight Planet s distance form sun determine how long it will take to orbit sun Mercury (closest to sun): 88 days to orbit sun Earth: 365.25 days (reason for leap year) Neptune (farthest): 165 years (60, 225 days) Diameters of large planets (Jupiter, Saturn) only fraction of the sun 2

Satellites Orbit Objects with Larger Mass Satellite object in orbit around a body that has a larger mass o Moon is Earth s satellite First four planets: small, rocky with few or no satellites o Mercury (none), Venus (none), Earth, Mars Next four: large, gaseous with many satellites o Jupiter, Saturn, Uranus, Neptune We know of 135 satellites in our solar system o 1970: we only knew of 33 Satellites Space missions have discovered many small satellites o More could be found in future Smallest are less than 3 km in diameter Largest moons in our solar system (Jupiter s Ganymede and Saturn s Titan) are larger than planet Mercury The Moon Orbits the sun indirectly o Orbits Earth at distance of 384,000 km Surface is covered with craters as a result of smaller bodies crashing into it Maria, large dark patches on the moon, are areas of lava that flowed out from interior to fill in craters, later cooling to solid rock Like the sun, the moon affects life on Earth through its movements and gravitational influence Moon has Phases because it Revolves around Earth Phases moon s appearance to have different shapes throughout the month o Relative positions of the Earth, moon, and sun determine phases At any given time, sun illuminates half of the moon o As moon revolves around Earth, illuminated portion that faces Earth changes o Full moon: half that is lit is facing you o New moon: side that is dark is facing you From one full moon to the next = 29.5 days or one calendar month o Many calendars are based on the movement of the moon Eclipses Eclipse when Earth, sun, and moon are in a straight line o Occurs when one object moves into the shadow of another object During new moon, moon may cast shadow onto Earth Solar eclipse sky turns dark as moon blocks the sun Lunar eclipse full moon passes in front of Earth s shadow during nighttime 3

Moon Affects Earth s Tides Tides are mainly result of gravitational influence of the moon o Pull is strongest on side nearest to the moon..why? Water is pulled toward moon, but so is solid earth o We notice water movement more because it is liquid Because Earth rotates, one area on Earth will have two high tides and two low tides in a period of 24 h 50 min o These tides change throughout month because moon is orbiting Earth Sun has impact but it is minor o When sun is on same side of Earth as moon, g-forces are strongest and tides are highest for the month 19.2 The Inner and Outer Planets Key Ideas: o How are the inner planets similar to one another? o What are gas giants? o What type of bodies lie beyond the gas giants? Terrestrial planet Hydrosphere Asteroid Dwarf planet Gas giant Key Terms The Inner Planets Terrestrial planets highly dense planets nearest to the sun: Mercury, Venus, Earth, and Mars These terrestrial planets are relatively small and have solid, rocky surfaces Planets have similar compositions and share many similar surface features o Metallic cores o Rocky surfaces with some of same terrain features as Earth o Mountains, canyons, and craters 4

Mercury has Extreme Temperatures Mariner 10 first probe to investigate Mars Mercury is covered with craters Never very far from sun, small orbit around the sun Distances in solar system measured in distance of Earth to the sun o 1 Astronomical Unit (AU) = 150 million km Mercury is 0.4 AU o Surface temp can reach 720 K during day (836 F) o Night surface temp can reach 103 K (-274 F) Has almost no atmosphere and no water 1 day lasts 59 Earth days I year lasts 88 Earth days Mercury Venus and Greenhouse Effect Venus is 0.7 AU from sun Can be seen near sunrise or sunset o Often called morning or evening star Surface has numerous mountains and plains Spins very slow and in opposite direction than most of other planets and sun 1 day is 234 Earth days, 1 year is 225 Earth days Does not provide environment to support life Hot and atmosphere has large amounts of sulfuric acid Venus Atmospheric pressure is 90 times greater than Earth Thick carbon dioxide atmosphere traps sun s heat o Causing runaway greenhouse effect o Raises temperature greater than 700 K Earth s Ideal Conditions Only planet we know that sustains life Only planet that has large amounts of liquid water on its surface Hydrosphere all the water on Earth s surface, both liquid and frozen state Hydrosphere helps moderate temperature of Earth Atmosphere Protects Earth Atmosphere = 78% nitrogen, 21% oxygen, 1% argon, carbon dioxide, other gases Helps moderate temperatures between day and night o Greenhouse effect makes sure that surface does not freeze at night Blocks radiation and high-energy particles from sun Also protects from space debris, man made and rocks o Most burn up when trying to enter, only large ones make it through Early atmosphere contained more carbon dioxide, methane, and ammonia o Microbes changed atmosphere, then later by plants 5

Missions to Mars Viking 1 and Viking 2 landed on surface in 1976 o 2004 2 Mars rovers landed on surface Mars has two polar ice caps made up if frozen carbon dioxide and possibly water Features on the surface suggest water once flowed on the surface Has very thin atmosphere, mostly carbon dioxide Mars is 1.5 AU o Has 2 small satellites (Phobos and Deimos) o Mars mass is 11% of Earth s o 1 year is 1.9 Earth years, 1 day is 24.7 Earth hours o Temperatures range between 144 K to 300 K Mars Extreme Landform Volcano (Olympus Mons) is tallest mountain in solar system o Almost 3 times height of Mount Everest o Mars has no plate tectonics lava remains in same location and volcanoes can grow very large Many impact craters o Thin atmosphere doesn t burn up objects o Lack of liquid water slows down weathering of craters Surface is red because iron oxide in soil Frequent dust storms stronger than those in Sahara o Form large red dunes Mars Asteroid Belt Lies between Mars and Jupiter Rocky objects ranging between 3 km and 700 km o Asteroids small solar system bodies Asteroid Ida is 58 km long and large enough to have captured its own small satellite (Dactyl) Asteroids rarely leave the belt but some wander away and may enter Earth s orbit Ceres is largest celestial body in the belt o Diameter of 940 km, once considered a planet due to tis size o Considered a dwarf planet celestial body that orbits the sun, round because its own gravity, but has not cleared its own orbital path The Gas Giants Gas giants Jupiter, Saturn, Uranus, Neptune Outer planets are much larger than inner planets and have thick, gaseous atmospheres, many satellites, and rings These planets have no solid surface o Spacecraft cannot land on them Pioneer missions in 1972 and 1973 Voyager 1 and Voyager 2 in 1977 Galileo in 1989 Cassini-Huygens reached Saturn in 2004 All Gas Giants Have Rings and Satellites Saturn rings were discovered in 1659 Modern technology discovered thin, faint rings of other gas giants o Uranus rings were discovered in 1977 Most of known satellites were discovered by space missions o Jupiter has more than 60 o Saturn has more than 40 o Uranus has at least 27 o Neptune has at least 13 o Most are cratered and some have thin atmospheres 6

Jupiter is Largest Planet 1,300 times that of Earth o If it were a mere 80 times larger than it currently is, it would be a star Distance: 5 AU 12 Earth years to orbit sun 1 day is less than 10 Earth hours Has swirling clouds of hydrogen, helium, methane, and ammonia Has feature known as Great Red Spot o Giant hurricane twice size of Earth; going on for hundreds of years 1610: Galileo discovered Jupiter s 4 largest satellites o Ganymede, Callisto, Io, Europa o Io has thin atmosphere and active volcanoes o Europa may contain liquid water under its icy surface Saturn s Ring System 95 times mass of Earth Takes more than 29 years to orbit sun 1 day takes 10.7 Earth hours Rotates fastest at equator has many satellites and ring system Rings are tiny particles of dust, rock, and ice o Size range from few millimeters to several meters; most are large snowball Competing gravitational forces hold particles in place Some rings are thin while others are 10 km to 20 km o Scientists are unsure why they formed Saturn Saturn: Still Forming? Radiates 3 times as much radiation as it receives Helium may be condensing and falling inward As helium nears the central core, it heats up Eventually the extra heat is radiated away When atmospheric helium is used up, it will reach state of equilibrium Uranus and Neptune: Blue Gas Giants Large planets with thick atmosphere of hydrogen, helium and methane o Methane gives the blue coloring William Herschel discovered Uranus in 1781 o Name given form mythology o Size of 14 Earth masses o 84 years to orbit sun and is 19 AU Scientists used what they knew about gravity to guide search for other planets Changes in expected orbit of Uranus could be used to predict existence and position of other planets Neptune Discovered in 1846 by Johann Galle Size is 17 Earth masses 165 years to orbit the sun and is 30 AU Gas in both planets atmosphere is 58 K 1 day on Uranus is about 17.25 hours o Pole is tilted at 98 degree angle; most extreme seasons of solar system o Few clouds and has wind speeds of 200 to 700 km/h 1 day on Neptune = 16 hours o Storm systems similar to Jupiter o Wind speeds up to 1,100 km/h 7

Beyond Gas Giants Beyond the gas giants are numerous small bodies Composed of ice and rock Until 2006, the word planet never had a clear scientific definition International Astronomical Union (IAU) defined what a planet is o Pluto was taken off of planet list because it has not cleared its orbital path o It is considered a dwarf planet Pluto is 0.002 Earth s mass, distance is almost 40 AU, and 1 orbit takes 248 Earth years Objects Beyond Neptune Kuiper Belt is populated by small bodies of ice and rock, containing Pluto Scientists think these are remnants of material that formed early solar system Recently, large bodies have been found o Called Eris o Also a dwarf planet with distance of 90 AU 19.3 Formation of the Solar System Key Ideas: How did early astronomers understand and describe the solar system? How did our solar system form? How did Earth s moon form? Early Astronomy Group of stones in Nabta, Egypt may be earliest record of human interest in astronomy o Possibly 6,000 to 7,000 years old o Thought to line up with the sun at the summer solstice Stonehenge is thought to be world s oldest observatories Early Models of the Solar System Early models only included objects in our system o Limited technology, only used naked eye Ancient Greeks observed sky to keep track of time They used logic and math, especially geometry Aristotle tried to explain phases of the moon and eclipses o His model was geocentric or earth-centered 140 C.E.- Ptolemy added to Aristotle s model o Thought sun, moon, and planets orbited Earth in perfect circles o Although incorrect, it helped astronomers predict many astronomical events for more than 1,000 years Early Models Nicolaus Copernicus realized that the sun was the center heliocentric in 1543 1605 Johannes Kepler revised Copernicus model Proposed orbits are ellipses or ovals o We use this model today 8

Elliptical Orbits Before 1687, paths planets take could be described but not the reason they stay in orbit Newton explained that gravity kept planets orbiting the sun and satellites orbiting planets Newton explained that it did not only apply to planets RECALL every object exerts force on another Everything in the universe follows same rules and acts in the same predictable way Ideas are basis for much of astronomy and physics How Did Solar System Form? Use the age of meteorites to estimate age of solar system think it formed 4.6 billions years ago Currently accepted model is the nebular hypothesis Nebula large cloud of dust and gas in space Hypothesis states that planets formed when small particles in a nebula collided and stuck together in a process called accretion Hypothesis also explains: o Why terrestrial and gas giants differ in composition o Why the orbits of the planets are almost circular o Why the planets are almost in the same plane Nebular Hypothesis Nebular Hypothesis Nebular Hypothesis Other Objects in Solar System Satellites, comets, asteroids, meteoroids Satellites objects that orbit larger objects Comets small bodies made of rock, ice, and dust that move around the sun in very elliptical orbits Asteroids small rocky objects found mainly between Mars and Jupiter Meteoroids smaller pieces of rock that move through space 9

Why Study Comets? Comets contain dust and ice made from methane, ammonia, carbon dioxide, and water 1994 comet Shoemaker-Levy hit Jupiter o Showed comets also contain silicon, magnesium, and iron Scientists have learned more about materials making up solar system Comets form tails of gas when passing the sun o Some have two tails: one is ion tail made of charged particles that always points away from sun o 2 nd tail is dust tail that follows comet s orbit Where do Comets Come From? As solar system formed, some small planetesimals did not join others They moved far away from the sun and developed very long orbital periods These make up the Oort cloud: shaped like a sphere and may be 100,000 AU wide Planetesimals that stayed in in nebula disk formed the Kuiper Belt Kuiper Belt located beyond orbit of Neptune Most comets come from this region What Are Meteorites? Rocks and other objects in space frequently enter Earth s atmosphere o Most burn up o Many large rocks form space that survive Earth s atmosphere come from asteroids Rocks that reach Earth s surface are called meteorites Three major types: Stony rocky materials, carbon compounds, water Iron iron and nickel Stony-iron both rocky metallic material Most known meteorites are stony with similar composition to Earth and the moon Effects of Meteorite Impacts Earth has close to 100 craters larger than 0.1 km in diameter Barringer Crater in Arizona o Meteorite with mass of 200,000 metric tons o More than 1 km wide and 175 deep o 25 metric tons of iron meteorite pieces have been found Many scientists think large asteroid or comet hit Earth 65 million years ago, killing dinosaurs Impact thought to equal 10 million hydrogen bombs Impact would have thrown dust into atmosphere o Made sky dark, killing plants and those that eat them, then meat eaters had no food How Did Moon Form Earth and moon are made of similar but not identical materials New theory states moon broke off from Earth when large objet hit Earth about 4.5 billion years ago o Much of Earth was molten or melted Scientists think moon formed from Earth s crust and mantle, along with iron from object that hit Earth Exoplanets Exoplanet planetlike object that orbits a star other than our sun Too faint to see with optical telescopes As exoplanet orbits star, its gravitational force pulls on the star, causing it to wobble o Scientists look for these wobble events Scientists have only found large exoplanets because they exert larger g-force = bigger wobble Have discovered exoplanets similar in mass to Jupiter or Saturn 10