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Unit 8 Chapter 27 The Planets of the Solar System Section 1 The Formation of the Planets Solar System The solar system is the sun, the planets and other bodies that revolve around an object. (for us it is Mr. Sun) Planet A planet is a primary body that revolves around a sun. The Nebular Hypothesis In 1796, French Mathematician Pierre-Simon, Marquis de LaPalce advanced the hypothesis that we have called the Nebula Hypothesis. Solar Nebular is a rotating cloud of gas and dust from which the sun and planets were believed to be formed from. The cloud may have come from either exploding stars or colliding stars and even material left over from the start of our universe. The cloud starts to shrink either under its own weight or because a near by star explodes. Most of the materials move towards the center and became very hot. Then the cloud starts to shrink and spin, eventually an eddy (whirlpool) forms. The interior gets hot material compresses together (hydrogen fusion start) - a star (our sun) is created. Smaller eddies compact into proto planets (or planetesimals) which later forms planets, moons, comets, meteorites, asteroids and dust. Formation of the Planets The Proto Planet Hypothesis (was also known as the Nebular Hypothesis) 1944 Von Weizsacker proposed the hypothesis 1950 An American astronomer named Kuiper modified it A gigantic rotating (spinning) cloud of dust and gas was gradually transformed into the sun, the planets, their natural satellites and other bodies to make the solar system. This happened about 4.6 billion years ago. Planetesimals are small bodies from which a planet originated from in the early stages of the development of the solar system. Dwarf Planets are smaller bodies that gathered mass but not enough to become a larger body like a planet. The Formation of the Inner Planets Four planets that are closer to the sun contained most of the heavy materials. They then lost most of the lighter gases because the gravity was not strong enough to hold on to it. They became smaller, rockier and denser than the outer planets. The Formation of the Outer Planets These planets formed further away from they sun, they became colder, less dense than the rocky inner planets. They kept their gases and the lighter ices. They came to be known as the “Gas Giants”. Pluto – The First Dwarf Planet Pluto was discovered in 1930 and was at that time known as the 9th Planet. Unfortunately it did not follow the characteristics of the outer planets and in 2006, Pluto lost it’s planet status. It was named a Dwarf Planet. The Formation of Solid Earth When Earth was formed it was hot. The sources of the heat were from the original collision with space debris, the compression of the materials forming layers and the decay of radioactive material. Early Solid Earth In its early stage, the Earth had only three layers ► Core – iron and nickel ► Mantle – iron and magnesium ► Crust – silica rich material Present Solid Earth As it cooled, the lighter materials rose to the surface and formed the continents. Then the atmosphere underwent drastic changes. The Formation of Earth’s Atmosphere Earth’s Early Atmosphere The early atmosphere was extremely deadly. • It took millions of years • H2O(V) - water vapor • *CO2 - Carbon dioxide • SO2 - Sulfur dioxide • CH4 - Methane Outgassing The internal heat caused volcanoes to erupt releasing gases into the atmosphere. Some of the gases released were carbon dioxide, nitrogen, methane, sulfur dioxide, ammonia and WATER VAPOR. A breakdown started to occur due to solar radiation which caused the molecules to break apart and then reform other elements. One of which was Ozone. Earth’s Present Atmosphere After this the atmosphere became conducive to growing life. As one celled plants developed into multiple celled ones, photosynthesis kicked in. Plants used the carbon for food and released the oxygen for our life. The Formation of Earth’s Oceans Some scientists believe that the early oceans were fresh water bodies. They feel that some of the water may have come from space in the form of comets colliding on earth. Over millions of years, rainwater fell to Earth and ran over the land, through rivers, and into the ocean. The rainwater dissolved some of the rocks on land and carried those dissolved solids into the oceans. As more dissolved solids were carried to the oceans, the concentration of some of these chemicals combined to form salts. Over millions of years, water has cycled between the oceans and the atmosphere making the water concentration more salty. The Ocean’s Effect on the Atmosphere The oceans affect global temperatures in a variety of ways. One way the oceans affect temperature is by dissolving carbon dioxide from the atmosphere. Scientists think that early oceans also affected Earth's early climate by dissolving carbon dioxide. Carbon dioxide in the atmosphere keeps energy from escaping into space and thus helps to heat the atmosphere. Section 2 Models of the Solar System Early astronomers came up with the idea that everything revolved around the Earth. Early Models 2000 years ago Greek Philosopher Aristotle suggested a Geocentric Model. He thought that the earth is the center of everything and all things move around it. It explains all facts including retrograde motion. It is proved to be very complicated. Still it was used until the 16th century. RETROGRADE MOTION It is the apparent backwards motion of the planets as they move across the sky nightly. Earth examples: 1. Passing cars just as you pass the car both cars seem to be moving the same speed 2. Sitting in a car-a car next to you starts to move and you think you are moving In 1543 Polish scientist Nicolaus Copernicus stated that it is a Sun centered solar system. This became the basis for our modern system. It explains all facts even retrograde motion. Another Astronomer who helped us with our present model was Galileo Galilei. He was the first person to use a telescope to look at the stars and planets. He went blind from looking at the sun. He also discovered moons around Jupiter which supported the heliocentric law. Kepler’s Laws • A 16th century Danish Nobleman, Tycho Brahe made very precise measurements of the stars, the planets, and their movements. He did this without a telescope. He kept a journal and had many students and assistants who studied his findings. • Johannas Kepler was one of his assistants. He studied all of Brahe’s notes and developed the “LAWS of Planetary Motion” which we use to explain all planetary motions. Law of Ellipses All planets move in Elliptical orbits with the sun at one focus. There must be two foci. • ECCENTRICITY • Measures how unlike an ellipse is to a circle. • When the eccentricity is small (close to 0) the two foci must be closer together or in the same spot. This makes the shape closer to a circle. • This causes the planets to vary their distances to the sun at different times during their orbit. Eccentricity = distance between foci Length of major axis 0-perfect circle 1-line Eccentricities of the planets are in the reference table Because the earth’s orbit isn’t a perfect circle we are closer in the winter and further away in the summer. Law of Equal Areas Equal area law- as a planet revolves around the sun the planet marks out equal areas in equal time Law of Periods Used to be called the “Harmonic Law of Planetary Motion” Period2=Distance3 The further a planet is from the sun the longer it takes to revolve around it. The distance is in Astronomical Units (A.U.) or the distance from the earth to the sun. Earth is approximately 30km per second. Kepler's 3rd Law T in years, a in astronomical units; then T2 = a3 Discrepancies are from limited accuracy Planet Period T Dist. a fr. Sun T2 a3 Mercury 0.241 0.387 0.05808 0.05796 Venus 0.616 0.723 0.37946 0.37793 Earth 1 1 1 1 Mars 1.88 1.524 3.5344 3.5396 Jupiter 11.9 5.203 141.61 140.85 Saturn 29.5 9.539 870.25 867.98 Uranus 84.0 19.191 7056 7068 Neptune 165.0 30.071 27225 27192 Pluto 248.0 39.457 61504 61429 Newton’s Explanation of Kepler’s Laws Isaac Newton (1642- 1727) Came up with the universal Laws of Gravity and Laws of Motion English scientist and mathematician developed an explanation for what keeps the planets in motion. Law of Motion An object traveling a straight line will stay in motion at the same speed unless an external force changes something. Newton’s Model of Orbits • Universal Law of Gravity • Gravity is a force that exist between all objects that have mass. • Gravity=Mass (1) Mass (2) • Distance2 • It is only strong when at least one mass is very large and the distances are small. • Tides are the gravitational pull of the moon and the sun on our water. • The sun pulls the planets out of a straight line into an orbit around it. Escape velocity- the minimum speed needed to escape the earth’s gravitational pull -11.2km/sec or 6.9 miles/sec ~25,000miles/hour Section 3 The Inner Planets Inner Planets Terrestrial – small, solid land, very dense • Mercury, Venus, Earth, Mars • *Pluto - outer planet w/solid surface; not very dense: removed from our ESRT in 2006 • **See Reference Table for planet notes** Mercury It is the nearest planet to the sun It is the smallest terrestrial planet It has a magnetic field about 1% of Earth’s Mariner 10 photographed it in 1974 & 1975 It turns on axis once every 59 days Hot daytime (400oC) Cold nighttime (-200oC) Venus Magellan spacecraft mapped it in 1990 It is sometimes called Earth’s sister; similar diameter, mass & gravity It has a weak to non-existent magnetic field It rotates East to West It’s has thick, pale yellow clouds In 1985 2 balloons carrying weather instruments found mostly carbon, 3% nitrogen It is very hot 475oC Earth We studied it all year. It is the 3rd rock from the sun. Mars It is half Earth’s diameter It is 2/5’s Earth’s gravity It is colder; summer 27oC, Winter -125oC The atmosphere is 95% Carbon, 5% Nitrogen & Argon It has less than 1% pressure of Earth We are continually studying this planet now Section 4 The Outer Planets Outer Planets Jovian are larger and less dense Gas Giants Jupiter, Saturn, Uranus, Neptune Jupiter It is the 5th planet in the solar system. It rotates the fastest of all planets (once every 10 hours) It is the largest planet (2times the total mass of all planets combined) It has the strongest known magnetic field It radiates 2 times as much heat back into space as it receives It has a great red spot (rotates slower than rest of atmosphere) On December 7th, 1995 Galileo probe entered the atmosphere There are at least 63 moons Some Scientist feel that it has rings around it too Saturn The 6th planet It turns once every 10 hours It has rings of gas and dust surrounding it It has areas of rising and sinking gases that has caused the yellowish banded color It has the lowest density (it could float in water) It has about 60 moons Uranus It was not discovered until 1781 It is 19 times farther from the sun Its average temp is -200oC It turns on its axis 17.2 hours It also has about 12 thin rings around it It has a sideways rotation which could have been caused by being knocked by a large object Voyager 2 flew past it in 1986 and discovered its magnetic field is about 60% off from the rotation About 27 moons Neptune It was discovered in 1846, after it was mathematically predicted In 1989 Voyager 2 discovered the magnetic axis is tipped 47% It has strong winds; 2000km per hour It has a temperature of -225oC The atmosphere is hydrogen (74%); helium (25%); methane (1%) It changes position with Pluto every 248 years and lasts about 20 years It has about 13 moons Some Scientists feel that it has some rings around it Objects beyond Neptune Pluto • Has the smallest everything (smaller than our moon) • It has a diameter is 2,274 km (like from New York to Oklahoma City is 2140 km) • It has a moon Charon (about 1172 km diameter) along with 2 other moons • It has a Temp of approximately -235oC to 210oC • Pluto has been since removed from our solar system in 2006 and called a dwarf planet. Kuiper-Belt Objects The Kuiper belt contains 100’s of objects in a area beyond Neptune’s orbit. They are called TNO or Transneptune objects. Some are the size of Pluto and some are smaller chunks of ice. A few objects named Eris, Makemake, and Haumea are being considered as dwarf planets Exoplanets Exoplanets are planets discovered outside of our solar system. By studying them hopefully we can learn more about our solar system and our planets.