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Chapter 22 Touring our Solar System Solar System * Inventory • 1 Sun • • • • asteroids • comets • meteoroids • The list will continue to grow Planetary Properties * Order of planets * Sizes of Planets * Sun contains 99.9% of solar system's mass * Planets are relatively close to the Sun * Planetary orbits become more widely spaced with increased distance from the Sun • Distance roughly doubles with each planet (_____________________) * Planets all revolve counterclockwise * All planets have nearly the same orbital plane as the ecliptic except Pluto (170) and Mercury (70) Terrestrial and Jovian Planets * Terrestrial Planets (___________________________________________) * Inner planets * un * Closely spaced orbits * * Small sizes * Predominantly rocky surfaces * * High densities * Slower rotation rates * Weaker magnetic fields * No rings * * Thinner atmospheres, except Venus • Due to low escape velocity - speed needed to escape a planet’s gravity * Jovian Planets (Jupiter, Saturn, Uranus, Neptune) * * Far from the Sun * * Large masses * * * Low densities 1 * * * * * Faster rotation rates Stronger magnetic fields Many rings Thick atmospheres • Due to huge escape velocities Formation of the Solar System * * Cloud of gas and dust contracted * Contraction created heat and pressure * Sun formed at the hot center * Giant, cooler swirling matter surrounded * Cooler regions away from the Sun caused condensation and the formation of proto-planets (proto-planetary disks = ___________________) Earth and the Moon in Bulk * Physical Properties * Earth is more massive * Earth is larger * Earth is more dense * Earth has stronger gravity • • Escape velocity is more on Earth * Rotation rate is faster on Earth • Earth always sees the same side of the Moon’s face • ________________________ – rotation period is equal to the revolution period * Distance to the Moon is 384,000 km (240,000 miles) * Overall Structure * Effect of tides on Earth's rotation * Earth's rotation is slowing down about 2 milliseconds every century • Caused by the tidal effect of the Moon and Sun * The Moon is spiraling away from Earth until the two become synchronized • Eventually the Moon will be 550,000 km away • * Lunar Air * * Very little amounts of water frozen in the rocks * * Day temperatures can reach _________ * Night temperatures can reach __________ * No sound on the Moon The Surface of the Moon * * Dark areas meaning "seas“ * * Solid basaltic lava flows * 3.2 - 3.9 billion years old 2 * * * Front side has more mare than back side Largest feature – Mare Imbrium (sea of rains) Distinctive Mare • Oceanus Procellarum – “Ocean of Storms” • Mare Nubium – “Sea of Clouds” • Mare Serenitatis – “Sea of Serenity” • Mare Tranquilitatis – “Sea of Tranquility” • Mare Fecunditatis – “Sea of Fertility” • Mare Crisium – “Sea of Crises” • Mare Vaporum – “Sea of Vapors” * Lunar Highlands * Lighter colored uplands • Rocks are more than 4 billion years old • Heavily cratered * Craters * The moon is pocked with numerous craters * Craters result from constant meteoritic impact * Slideshow of craters * Lunar Erosion * No erosion is caused by weather * • 10km crater occurs every 10 million years • 1 m crater every month • 1 cm crater every few minutes • A steady "rain" of micrometeoroids eats the surface of the Moon Origin of the Moon * * A Mars sized object hit the Earth sending numerous pieces of debris into orbit around the Earth * Computer models suggest this possible scenario * Debris would have coalesced into a solid object * Mercury * * Very small planet (close to the size of our Moon) * Very dense, 2nd only to Earth * Has numerous craters * Difficult to see detail through a telescope because it’s so close to the Sun * Looks a lot like our Moon * Fast revolution (88 days) * Slow rotation (59 days) • 2 months long night • * Night temperatures - __________) * Daytime temperatures - (__________) • • Life could not exist at those extremes 3 * * * * * * * * No atmosphere because little gravity and hot temperatures would release air to space Meteoroids and harmful radiation always bombard the surface The poles are always very cold (-2350F) since the Sun’s angle is always very low Mercury's surface • Numerous craters • No signs of water or weather • Has some fault scarps Internal structure • Has a weak magnetic field (10X less than Earth) • Large, heavy iron-rich core • Unsure if core is liquid or solid • Solid core prevents tectonic processes Planet is dry and lifeless 4.6 billion years old * * * * * * * * * 2nd brightest object in night sky next to the Moon • Covered in veil of clouds 225 day orbit Very slow rotation (243 days) • Similar to Earth in size, density, mass, and location (__________________) Surface • Can't see the surface because of clouds • • Map of Venus vs. Earth • Has mostly a smooth surface with rolling plains • Erosion by the atmosphere is prominent • – Most pronounced features are volcanic – Large pancake lava domes exist – Flattened due to high atmospheric pressures – Resembles shield volcanoes on Earth – No active volcano has yet been observed – Rocks resemble basalt and granite • – The 2 Landers lasted about an hour and eventually melted the circuitry due to intense heat – Very few visible craters Internal Structure • – Most likely due to the slow rotation • Believed to be similar to Earth but with a softer crust due to the high temperatures 4 * * * * * Atmosphere • Average surface temperatures are near 9000F • 96.5% carbon dioxide and 3.5% nitrogen – • Constant lightning strikes with atmospheric pressures 90 times more than on Earth Venus has no moons Life probably never existed on Venus It’s sobering to realize how a planet so much like the Earth but just a little closer to the Sun could have evolved so differently Mars * * * Rotation period of 24.6 hours * Atmosphere • Thin layer of CO2 • 1/150th of Earth’s atmospheric pressure • Mars has clouds and storms • 95.3% carbon dioxide • 2.7% nitrogen • 1.6% argon • Water vapor, oxygen, and carbon monoxide * Surface • Frozen polar ice caps of H2O and CO2 – Polar caps grow and shrink with changing seasons • Numerous large volcanoes – – Tharsis Ridge (Bulge) – Currently unknown if volcanoes are active • Huge canyons exist – _______________ is a canyon much larger than the Grand Canyon – Was not formed by running water – Large crack formed as the Tharsis Ridge formed – Flowing water is thought to create most canyons • The northern hemisphere is more flat while the southern hemisphere is more cratered • Evidence of flowing water on Mars – Runoff and outflow channels observed – – Water seepage from hillsides – – Springs from within a hill – Ancient meandering stream channels • – When the volcanism stopped the atmosphere was no longer provided with water vapor and the land dried up 5 * * • Mars has huge global wide dust storms Several missions have landed on Mars • Currently “Opportunity” and “Spirit” missions Internal Structure • No known magnetosphere • Core must be non-metallic, non-liquid, or both * * * • Temperatures can reach 700F near the equator during the day * Mars has 2 moons (Phobos, Deimos) • Very small and irregularly shaped • Thought to be captured asteroids * Mars photo slideshow Jupiter * * 21/2 times the mass of all the other planets, asteroids, and satellites combined * If Jupiter was 10 times more massive, it would have been a star * 3rd brightest object in night sky (telescope view) * • Rotation = 9.9 hours, Revolution = 11.86 years • Atmosphere experiences differential rotation * Small tilt axis of 3 degrees * Atmosphere • Primarily H (86%) and He (14%) • Parallel cloud bands exist – Bands caused by convection from below • ______________________ – a storm system 2 times the size of Earth – A huge storm with smaller storms embedded – Rotates like a huge hurricane • Extensive colors in the atmosphere • Extremely turbulent atmosphere • Winds can reach 700 mph • Probes reveal Jupiter’s atmosphere is layered * Interior Structure • Internal heat source produces huge convection – Jupiter emits twice as much energy as it receives • Huge magnetosphere (larger than the Sun) • Outer core is liquid metallic hydrogen • Very intense pressure in Jupiter • Central temperature can reach 40,000 K • Surface may be a gigantic ocean of liquid H • Small central rocky core * * Jupiter has a thin ring system Saturn * • Recent evidence reveals the rings may be slowly disappearing 6 * * * * * * * * Saturn as viewed from Earth • The changing views of Saturn’s rings Fast rotation • Rotation = 10.5 hours, Revolution = 29.6 years Has great differential rotation Tilt axis of 27 degrees Atmosphere • Similar atmosphere to Jupiter – 92.4% H – 7.4% He • Atmospheric color not as vivid as Jupiter • Clouds are thicker than on Jupiter • Winds can exceed 930 mph • Huge storms exist • Very turbulent atmosphere • Interior Structure • Extensive magnetosphere produces aurora • Much like Jupiter • Thinner metallic hydrogen outer core • Smaller rocky core * Uranus (telescope view and VLT image) * * Kepler's law could not predict the exact path, so this meant another planet must be farther out past Uranus * Much less massive than Jupiter and Saturn * Nearly a twin to Neptune * • Currently unknown why it's tipped over * Uranus has rings as well * Atmosphere • Hydrogen 84% • Helium 14% • Methane 2% • Blue color is due to the methane content • Uranus is greenish compared to Neptune * Rotation = 17 hours, Revolution = 84 years * Has a central rocky core * Has 27 moons Neptune (Hubble view) * 1st planet discovered using mathematical predictions * Bluish fuzzy disk through a telescope * Slightly smaller than Uranus * * Rotation period = 17 hours 7 * * * * Revolution period = 165 years Atmosphere • • High frozen cirrus clouds • Winds can reach 1250 mph (windiest planet) • Hydrogen 84% • Helium 14% • Methane 2% • Neptune has rings Neptune has 13 moons * * * * Discovered in 1930 by Clyde Tombaugh • Partially named after famous astronomer, Percival Lowell, who searched for the 9th planet until his death in 1916 Dirty frozen snowball Recently demoted to dwarf planet status • More resemblance to a large Kuiper Belt Object (KBO) than a planet * • Recent findings reveal 2 more possible moons Small Solar System Bodies * Meteoroids * Rocky fragment less than 100 m in diameter * • Caused by friction heating up an object entering Earth's atmosphere * Typically lasts for only a few seconds * Meteorite * ____________________ - Earth passes into the remnants of an old comet’s tail • Prominent events calendar * Most are sand sized particles * Primarily composed of iron and nickel * Friction scars the meteoroid’s surface * 4.4 - 4.6 billion years * * Over 250,000 known asteroids * Fragments of rocky material more than 100 meters in diameter * Most are found in the Asteroid Belt • * Revolve counterclockwise, except one * Most stay close to the ecliptic plane * More eccentric orbits than the planets * • Share an orbit with Jupiter • Remain 600 ahead and behind Jupiter in orbit * • Also known as “Near Earth Objects” (NEO) 8 * * • Most asteroids will remain within the belt • Some have highly elliptical orbits • Over 3000 known • Current map of objects • Become deflected by the gravities of Mars and Jupiter • • most are less than 1km wide, but one is greater than 10 km • Icarus (mile-wide) is an Earth-crossing asteroid Largest asteroid “Ceres” is 587 miles wide Asteroid views • close-up view -- Irregular shaped -- Rotating Landed on asteroid Eros in 2001 Asteroids originate from the fragments of broken planets and rocks that never formed * * Comets * Discovered as a faint, fuzzy patch far from the Sun * Mostly icy with some rocks and typically 1-10 km wide * They brighten and develop a tail as it nears the Sun * Have no internal light, only reflected * Comet features * Nucleus – • Only the nucleus exists far from the Sun * __________ - heated mass forms a gaseous and dusty glow around the nucleus • coma gets larger as it nears Sun • can be as large as Jupiter * Tail • Largest portion of a comet • can stretch a distance of 1 AU • – ion tail – – dust tail - curved white tail of comet • Tails are faced away from the Sun * Hydrogen envelope - engulfs the coma and the tail * Famous comets * Hale-Bopp (1997) * Hyakutake (1998) * • 76 year period • Documented every time since 240 B.C. • In 1986, it was probed by ESA • Will return in 2061 * Origins • Short period comets originate in the _________________ – Periods less than 200 years • Long period comets originate in the __________________ – Can stretch up to 100,000 AU – Surrounds the entire solar system 9 * Comets have highly elliptical orbits * They get smaller with each pass since they melt a little each time they pass by the Sun Is Earth on a Collision Course??? * The solar system is cluttered with meteoroids, asteroids, comets, and comet remnants which travel at great speeds * We know that comets and asteroids have collided with Earth more frequently than 1st expected * Evidence of impacts * Earth is littered with over 100 impact structures called "____________“ and many are very old • Meteor Crater – Winslow, AZ – 25,000 years ago – 1.2 km wide, 0.2 km deep – Meteoroid was about 50 m wide • Gosses Bluff (Australia) – 140 million years ago • Manicouagan Crater (Canada) – 200,000 million * Recent incidents • – In 1908, a spectacular explosion occurred in Siberia from a "fire-ball" brighter than the Sun – Shock waves broke windows 1000 miles away – Trees were scorched, de-limbed, and flattened up to 19 miles away – – Object exploded just above the surface • – – Produced brilliant flashes and dark zones • Asteroid 2002 MN – 100 meter object passed within 75,000 miles of Earth (1/3rd the distance to the Moon) – It was detected 3 days after it passed our planet • – In April 2029, this object will pass only 15,000 miles above Earth’s surface (15 times closer than the Moon) – Has a 350 meter diameter * “Sooner or later” these objects will come back and make an impact End of Chapter 22 Touring our Solar System 10