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Pearson Prentice Hall Physical Science: Concepts in Action Chapter 25 The Solar System 25.1 Exploring the Solar System • Objectives: • 1. Compare and contrast the geocentric and heliocentric models of the solar system • 2. Describe the orbits of the planets around the sun and explain how gravity and inertia keep the planets in orbit • 3. Name the components of the solar system • 4. Identify different technologies used for exploring the solar system Geocentric vs. Heliocentric • The geocentric model is from ancient Greece • In the geocentric model, Earth is stationary while objects in the sky move around it • In the heliocentric model, Earth and the other planets revolve around the sun • Imagine the path of Earth’s orbit traced on a table • Def: the ecliptic plane is the path of Earth’s orbit Gravity plus Inertia & Components of the Solar System • Gravity and inertia combine with each other to keep the planets in orbit • Without gravity, planetary inertia would cause them to fly off in space • The components of the solar system are the sun, the planets, their moons, and a variety of smaller objects that mostly revolve in the same plane around the sun Exploring the Solar System • Modern technology including telescopes, piloted spacecraft, & space probes has allowed scientists to explore the solar system • Def: a space probe in an unpiloted vehicle that carries scientific instruments into space and transmits information back to Earth • NASA launched 2 vehicles, Spirit & Opportunity to land on Mars in 2004 for a 3 month mission • They are still sending information back to Earth today • The scientist who monitors them is at UNR 25.2 The Earth-Moon System • Objectives: • 1. Explain why the moon lacks atmosphere & the effect this has on the range of temperature on the moon • 2. Describe the features of moon’s surface • 3. State a theory about the formation of the moon • 4. Explain the phases of the moon, tides & eclipses & interpret diagrams of these events No Atmosphere/Surface Features • Moon’s gravity is too weak to hold onto gas molecules • The lack of atmosphere allows moon’s surface temperature to vary tremendously • The major surface features are maria, highlands and craters • Def: maria are low, flat plains formed by ancient lunar lava flows Features plus Formation • Def: highlands are rough mountainous regions that cover most of moon’s surface • Lunar highlands are light-colored areas that surround the maria • Def: craters are round depressions caused by the impact of high speed meteoroids • Def: meteoroids are chunks of rock that move through the solar system • Scientists hypothesize that the moon was formed after an enormous collision in Earth’s history • The collision was probably caused by rocky debris which was plentiful & hit many planets about 4.6 billion years ago when Earth formed Phases of the Moon & Eclipses • Def: the different shapes of the moon visible from Earth are called phases • The moon’s phases are caused by changes in the relative positions of the moon, sun & Earth as the moon revolves around the Earth • Def: an eclipse occurs when the shadow of one body in space falls on another • Def: a solar eclipse occurs when the moon casts a shadow on a portion of Earth’s surface • Def: a lunar eclipse occurs when Earth casts a shadow on the moon 8 Phases of the moon New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse). Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight. Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing . Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Lunar Eclipse Tides • Def: tides are the regular rise and fall of ocean waters • Tide are caused mainly by differences in the moon’s gravitational pull on Earth • The sun’s gravity affects tides about half as much as the moon • Def: spring tide is the combined forces of the gravity of the sun and the moon • Def: neap tide is the least tide possible & is due to first or third quarter moon being at right angles to the Earth (compared to sun’s position) • The solar system is the sun and the planets that orbit around it • The four planets closest to the sun are the terrestrial planets • Def: terrestrial planets are planets similar in structure to Earth • The four inner planets are all small, dense and rocky • All have a crust, mantle and iron core • Five planets have been known for centuries: Mercury, Venus, Mars, Jupiter & Saturn 25.3 The Inner Solar System • Objectives: • 1. Compare the terrestrial planets and describe characteristics of each • 2. Define asteroids and state alternative hypotheses about how they were formed Compare and Describe • Mercury is the smallest and closest to the sun • Venus is called the evening star or morning star • Venus’s atmosphere has the greenhouse gas effect due to large amounts of CO2 which traps heat and raise temperature • The CO2 also causes it to rain sulfuric acid when it combines with the sulfur in the atmosphere • Earth’s atmosphere is suitable for water to exist as a liquid • Mars is a major source of study right now, including experimentation with rovers from NASA named Spirit and Opportunity • They landed on Mars in 2004 • The rovers were designed to send information for 3 months, but functioned for years yielding information about Martian water and soil • Spirit was mobile on the Red Planet for over five years and then functioned as a stationary science platform for another year before getting killed off by a Martian winter it couldn’t avoid” • As of January 2012, Opportunity still works & will spend the Martian winter in a sunny spot until the engineers wake it up in Martian spring • In August 2012, NASA landed a much larger, very expensive rover called Curiosity • Its mission is to see if Mars ever had the right conditions to support life • Mars shows evidence of having had a lot of water in its past • other missions to Mars, including manned missions are being considered • Mars is sometimes called the “red planet” Asteroids • Def: asteroids are small rocky bodies orbiting the sun • The region in the solar system where they are found is called the asteroid belt • The asteroid belt is between Mars and Jupiter • Scientists hypothesize that asteroids are remnants of the early solar system that never came together to form a planet The Inner Solar System 25.4 The Outer Solar System • Objectives: • 1. Compare the gas giants and describe characteristics of each • 2. Distinguish between planets and dwarf planets • 3. Distinguish between comets and meteoroids and describe their characteristics • 4. Locate and describe the Kuiper belt and Oort Cloud Gas Giants • The four outer planets (Jupiter, Saturn, Uranus and Neptune) are gas giants • Def: gas giants are planets composed mainly of hydrogen and helium • The four gas giants are thought to have small, dense cores, and dense atmospheres composed mostly of hydrogen and helium • Def: a ring is a disk make many small particles of rock and ice in orbit around a planet • All of the gas giants have rings • Jupiter is the largest and most massive planet in our solar system • Jupiter has at least 63 moons • Saturn’s rings are the largest and most visible from Earth • Saturn has at least 56 moons, but is known for its moon named Titan • Titan is larger than Mercury • Uranus is believed to have a mantle of liquid water and dissolved ammonia • The axis of Uranus’s rotation is tilted more than 90° • Neptune’s bluish color comes from the methane in its atmosphere • Its largest moon is called Triton and it has a thin atmosphere and an icy surface Dwarf Planets • Def: a dwarf planet, like a planet, is spherical and orbits the sun directly, but a dwarf has not cleared the neighborhood (more on that in a moment) • The definition of planet is that it is a celestial body in orbit around the sun, has self-gravity, is not a satellite and clears the neighborhood around its orbit • A satellite is any object orbiting a planet, whether natural or man-made • Pluto does not “clear the neighborhood” because it is part of a sea of objects that occupy the same region of space • Pluto and its moon Charon have an elliptical orbit that sometimes crosses into Jupiter’s orbit, thus lending support to those who want to reclassify it • Planets must have sufficient force to get other objects out of their way • Under the new definition as many a 12 planets have been proposed • Officially at this time there are 8 planets in our solar system • The astronomers in 2006 came up with the following proposals & definitions: • 1. Planets: The eight worlds starting with Mercury and moving out to Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune • 2. Dwarf planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite." • 3. Small solar system bodies: All other objects orbiting the sun • The Pluto issue will continue to play out for some time & is not yet settled Comets, Meteoroids, Kuiper & Oort • Def: comets are dusty pieces of ice and rock that partially vaporize when they pass near the sun • Def: meteoroids are pieces of rock, usually less than a few hundred meters in size, that travel through the solar system • At the edge of the solar system beyond Neptune are Kuiper and beyond Kuiper is Oort • Most of the objects in the Kuiper belt lie in a doughnut shaped region close to the ecliptic plane • Def: the ecliptic plane is the plane in space containing Earth’s orbit (the path of Earth’s orbit) • Pluto is in the Kuiper belt • Beyond the Kuiper belt is a great reservoir of comets called the Oort cloud • Occasionally objects from the Oort cloud enter the inner solar system as comets 25.5 The Origin of the Solar System • Objectives: • 1. State the nebular theory • 2. Relate the nebular theory to the orbits, composition and size of the planets The Nebular Theory • Scientists believe the solar system was formed by the nebular model • The nebular theory state that the solar system formed from a rotating cloud of dust and gas • Def: a protoplanetary disk is a large disk shaped cloud of dust and gas resembling a giant fried egg rotating in space • Most of the mass is concentrated in the center • The planets eventually formed from the outer parts of the disk • The central mass eventually became the sun • Def: planetesimals were asteroid-like bodies that eventually combined to form planets • Def: accretion is the process of adding mass by colliding with other planetesimals • The cloud may have been flat as it collapsed, laying in one plane creating the orbits • Accretion occurs when small particles collect and stick together to form large masses • planetesimals attracted more and more matter leading to moon sized protoplanets with their own gravity • The terrestrial planets ended up close to the sun and are small and rocky • This is because the inner solar system was too hot during formation for ice-forming compounds to condense • The gas giants are large and have low densities because the outer solar system was cool enough for ice-forming compounds to condense