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Ch 28 Formation of the Solar System Formation Theory: Based on direct observations and data from probes. The theory has to explain all observed facts such as the shape of the solar system, differences among planets concerning composition, size, and other solar system features such as asteroids, and comets. Ch 28 Formation of the Solar System Overview of solar system formation: When an interstellar cloud of hydrogen (nebulae) collapses, it forms a star when the temperature and pressure become high enough to fuse hydrogen into helium. The remaining part of the cloud surrounding the star became the rest of the solar system. Formation of the Solar System Formation of the Solar System Formation Details: Initially the density of the interstellar cloud is very low and the temperature is very cold. When the cloud begins to collapse under its own gravitational pull, it begins to: 1. Rotates 2. Accelerates 3. Contracts 4. Density increases 5. Pressure increases 6. Temperature increases Think of the cloud in a bottle you made. As you squeezed the bottle, the air molecules were forced to be closer together, and as a result the pressure and temperature increased. More details: As you might suspect, the temperature was warmer in the middle of this collapsing cloud. The differences in temperature throughout the cloud can account for why we have different elements throughout the solar system. Different elements will form at different temperatures. This is similar to Bowen’s reaction series and how different minerals and rocks form at different temperatures. More details: The planets that were closest to the warm center (rocky inner planets) are richer in the higher melting point elements while the outer planets are their moons are composed mostly of the more volatile elements (gasses and ice). More details: Before there were planets, there were the planetesimals! These are smaller planet like bodies that were orbiting the Sun. There were 100’s of them! They collided into each other like a cosmic game of pool, but when they hit, they ended up sticking together to form larger bodies, and eventually the planets. Gas Giants form: The first large giant to form was Jupiter. It increased in size due to the merging of icy planetesimals that contained mostly lighter elements. The larger it grew, the more gravitational pull it had, and the more it mass it could collect until it “cleared the neighborhood.” The other gas giants Saturn, Neptune and Uranus formed the same way. Terrestrial Planets form: The terrestrial planets also grew in size due to the collisions of the planetesimals. However, the planetesimals near the hot center of the disk were made of elements that could resist vaporization. Because of this, the inner planets are more dense. Debris: Material that remained after the formation of the planets is called debris. The planets swept up this debris in their path and became larger still. Some debris never formed planets and became: 1. The main belt (Asteroid belt between Mars and Jupiter. 2. The Kuiper Belt 3. The Oort cloud of comets Ch 28 Our Solar System I Early ideas A) geocentric model (Earth centered) 1. Could not easily explain observations a. Wandering planets (epicycle orbits) i Retrograde motion b. Speed of stars would be immense Retrograde motion: The apparent motion of the planets that makes them appear to move backwards because the Earth is on the “inside track” and passes other planets which are on more distant orbit. 2. Aristotle and Ptolemy’s ideas for a Earth centered universe beat out the Sun centered model. Since the Royalty and Religious leaders liked this idea, it became law, and to say otherwise could get you jailed, killed or worse (to them at least) excommunicated. B) Heliocentric model (Sun centered) back 1. Aristarchus. Thousands of years ago around the same time as Aristotle, this astronomer/mathematician came up with the Sun centered model. He also theorizes that the stars are like our Sun, but very far away. Unfortunately his ideas were not largely accepted and took until the renaissance period for it to gain credibility through men like Copernicus and Galileo. B) Heliocentric model (Sun centered) back 2. Nicolaus Copernicus’s idea a. Easily explained observations b. Not accepted by the church 3. Support grew for this idea a. Tycho Brahe made many observations for decades b. Kepler used Brahe’s data, made 3 laws i) Orbits in shape of ellipse with the Sun at one foci ii) Equal areas on the orbital plane are swept out in equal time. iii) P^2 = a^3 page 778 in text Keplers first law: The Earth’s orbit is in the shape of an ellipse We will draw and ellipse and calculate the eccentricity for the ellipse for a lab. The ellipse requires 2 foci points to draw it. You will measure the difference between the foci points in centimeters. Then you will measure the length of the major axis in centimeters. Next you will divide the foci point length by the major axis length. This formula is on your ESRTs cover. All values are between 0 and 1. A circle which looks like a 0 is 0! A straight line which looks like a 1 is a 1! 2. Kepler’s second law: An equal area is swept out in equal time. Kepler’s third law P^2 = a^3 The length of time it takes for a planet or other body to travel a complete orbit around the Sun is called its orbital period (P). The formula is shows the mathematical relationship between the size of the planets ellipse and its orbital period. “P” is time measured in Earth years, and “a” is the length of the semi major axis measured in astronomical units. Newton invents calculus 4. Galileo uses telescope to observe sky back a. Jupiter has its own moons (so not everything revolves around the Earth). b. Moon has craters (heavens not perfect) c. Sun has spots (blemishes) and rotates 5. Newton uses physics to explain solar system a. Quantifies (not discovers) gravity b. Establishes relationship of tides to Moon c. Creates calculus (Algebraic short cut) d. Explains math problems with orbits Newton discovered the relationship between the Moon, Sun and tides C. Gravity is explained by Newton back 1. Formula : Force = G (m1m2) pg 779 in text r^2 a. G is a constant value b. m1 and m2 are the two masses c. r is the distance between the masses and it is squared The center of mass for two objects of equal weight is half way between the two objects. The center of mass moves closer to the object that is heavier. An astronomical unit or AU is the average distance from the Earth to the Sun (1.49 X 10^8 km) 28.2 Terrestrial Planets Terrestrial Planets: The planets that are close to Earth’s size and have a solid rocky surface. Gas giant planets: Are the large and gaseous planets which lack a solid surface. Mercury: Closest to the Sun and revolves around the Sun the fastest (hence its name). It has a very thin atmosphere (oxygen and sodium atoms. Because the atmosphere is so thin it has wild swings in temperatures and ranges 427 C to -173 C in one of its days. An impact crater here would last a long time due to a lack of weathering and erosion. Mercury has large scarps on its surface, possibly due to the crust shrinking as the planet cooled. It is fairly dense and likely as a large iron and nickel core. Venus highlights: -Second planet from the Sun, it is the brightest in our sky because it is the closest to us, and has a high albedo. -Venus has a longer day than its year because it rotates so slowly. -Venus is the hottest planet with temps at 464 degrees C (even though Mercury is closer to the Sun) due to having a thick atmosphere with nitrogen CO2 so it has a major green house effect. -The clouds are made of sulfuric acid and the surface is too hot for liquid water to exist. Venus highlights: -Venus also has retrograde rotation: rotates clockwise (most planets rotate counter clockwise). This means the Sun appears to rise in the west and set in the east. This retrograde rotation may be the result of a major collision (this spin change can be observed and used while playing pool!) -The surface is smooth due to lava flows from 500 mya but not likely tectonically active like the Earth is. -Its size and density are similar to Earth so it is theorized that the internal structure is also similar. Earth: -Third rock from the Sun. -Vast amounts of liquid water on the surface. -Currently only Confirmed life in the Universe. -Signs of intelligent life. Mars (AKA The Red planet due to iron oxides) highlights: -Smaller and less dense than Earth -Two moons -We have landed rovers on Mars to explore -Largest volcano in the solar system called Olympus Mons. Its base is larger than the state of Colorado and it is 3 times taller than mount Everest. These volcanoes were created by a hotspot. There is no plate movement. Volcanoes such as this may have shot bacteria laced rocks into space which have hit the Earth. Did our life come from Mars? -Enormous canyons such as Valles Marineris which is 10 times longer than the Grand Canyon and 3 times deeper. -Thin atmosphere with a similar composition to Venus -Long lasting wind storms (weeks) -Erosional features show dried river and lake beds, outflow channels, and runoff channels. These suggest that liquid water once existed on Mars. Astronomers think that the climate used to be warmer which allowed for a water cycle. Currently the only know water on Mars is in ice form at the poles. Most of this ice is carbon dioxide aka dry ice. Jupiter highlights: -A gas giant and the largest planet in the solar system. It has 1/10th the diameter of the Sun and it is11 times larger than Earth in diameter -Has over 60 moons, but 4 large ones called the Galilean moons (Galileo discovered) Io, Europa, Ganymede, and Callisto. All but Europa are bigger than our Earth’s Moon. Europa may even have a sub surface ocean of liquid water due to the squeezing and heating caused by Jupiter's gravitational pull. -Has a unique compound called liquid metallic hydrogen which can only exist under really high pressure. -These gases act like liquids under such high pressure. -Jupiter has rings (not has large and defined as Saturns) -The core is made of rock and ice (possibly the size of Earth) -Jupiter has the shortest day (rotates the fastest 9 hours 50 minutes = one day) -This rapid rotation causes the clouds to flow rapidly as well And forms bands of alternating dark and light colors. Belts: low level dark colored warm clouds cools and sinks. Zones: high level, light colored (more ammonia ice) cool clouds that get warm and rise. The Great Red Spot: A hurricane like storm that could fit three Earth’s inside and has lasted for the last 400 years. Saturn -Gas giant slightly smaller than Jupiter. -Its average density would allow it to float in water (good luck finding a tub for that…) -Also rotates rapidly and makes a layered cloud system. -The atmosphere is made up of Hydrogen, helium with ammonia ice. -has a small solid core of rock and ice Saturn's Magnetic field is 1,000 times stronger than Earth And is aligned with its rotational axis (Rare among planets) -Rings are broader and brighter than other gas giants. These rings are made of pieces of ice that range from microscopic to house sized chunks. The particles to make these rings may have come from debris left over from the collisions of asteroids, comets, or the break up of a moon. Saturn has over 55 moons. -The largest is Titan which is larger than the planet Mercury. -Titan is unique because it has methane which can exist as a liquid, solid or gas on its surface. -In 2005 Cassini released the Huygens probe and found ice and water vapor which suggests geologic activity. -Titan has lots and lots of oil and natural gas. Uranus highlights: -Gas giant discovered accidently in 1781 when a blusish object was seen moving relative to the stars. -Has at least 27 moons -Dark and nearly invisible rings -Average temp -215 degrees C -4 times the diameter of Earth -Atmosphere is mostly hydrogen and helium (colorless) -Blue color due to Methane gas in atmosphere -No distinctive clouds or belts and zones. -Rotational axis is tipped over to the point where the north pole almost lies on its orbital plane (likely knocked sideways due to a collision. -Thus, each pole spends 42 years in darkness. Neptune -The existence of this planet was predicted before it was seen based on the laws of gravitation. -Discovered in 1846 where astronomers predicted it would be. -The last of the gas giants in our solar system. -Slightly smaller and denser than Uranus -Similar to Uranus in terms of atmospheric composition -Unlike Uranus, it does has distinctive clouds, belts and zones like that of Jupiter and Saturn. Other solar system objects -In the Early 2000’s, astronmers began to notice large objects in the Kuiper belt. One such object, now named Eris is the same size or larger than Pluto. The Astronomical community then re-evaluated what the definition of planet should be. They decided on a new classification called Pluto and others like it a Dwarf Planet. Others in this same region are called Sedna, 2005 fy9 (Easter bunny), EL61 Haumea, Buffy, and Makemake, Quaoar. -Ceres is another large object but not a Dwarf planet. It is not found in the Kuiper belt, but the main belt (in between Mars and Jupiter). In 1801 it was predicted that there would be a planet found between Mars and Jupiter. Instead they found an asteroid belt consisting of hundreds of thousands of objects. Ceres is considered to be the largest Asteroid. Small Solar System Bodies -Objects between Mars and Jupiter are called asteroids and the belt is called the Main Belt. -Objects beyond the orbit of Neptune care called trans-Neptunian objects or TNOs -Kuiper belt objects are termed KBOs -Comets belong to the Oort cloud Asteroids: Left over rock from the formation of the solar system. -Some are large enough to have their own natural satellites. -The total mass of all of the asteroids in the solar system is equivalent to about 0.08% of the Earth’s mass. -Meteoroid: Asteroid that enters the Earths atmosphere. -Meteor: The streak of light produced by a particle as it burns up in the atmosphere. Meteorite: If a meteoroid does not completely burn up and hits the ground. Kuiper belt: Asteroid belt (bodies made of rocks and ice) that lie beyond the orbit of Neptune (KBOs). Comets: Small icy bodies (1-10 km in diameter) that have highly eccentric orbits around the Sun. They are largely found in the area from the Kuiper belt out to 100,000 AU. This is known as the Oort cloud. Comet structure: When a comet comes within 3 AU of the Sun it begins to evaporate. As a result it forms a head and one or more tails. The head is surrounded by glowing gas and has a small solid core. The tail forms as the dust and gas are pushed away from the comet by particles and radiation from the Sun. This is why Tails always point away from the Sun. Periodic comets: Comets can get bumped out of the Oort cloud and head into the interior of the solar system. When they return repeatedly, they are called periodic comets. Halley’s comet comes back every 76 years. The last time was 1985 and the next time will be 2061. Meteor shower: When Earth crosses the trail of a comet, the particles burn in the atmosphere producing bright streaks of light called a meteor shower. Most meteors we see are caused by dust particles from comets. They are often named for the area in the sky in front of the constellation they appear to come from such as Leonids for the constellation of Leo or Geminids from Gemini. Meteor Shower Dates for 2016 Quadrantid Draco (NE) Jan. 4 60-100 2003 EH1 Lyrid* Lyra (E) April 22 10-20 Thatcher (1861 I) Eta Aquariid Aquarius (E) May 5 20-60 1P/Halley Delta Aquariid Aquarius (S) July 28 20 96P/Machholz Perseid Perseus (NE) Aug. 12 90** 109P/Swift-Tuttle Orionid* Orion (SE) Oct. 21 10-20 1P/Halley Southern Taurid Taurus (S) Nov. 5 10-20 2P/Encke Leonid* Leo (E) Nov. 17 10-20 55P/Tempel-Tuttle Geminid* Gemini (S) Dec. 14 100-120 3200 Phaethon - See more at: http://www.skyandtelescope.com/astronomynews/observing-news/meteor-showers-in-2016/#sthash.MhNAhkuj.dpuf Ch 28 notes quiz 1. What is a nebulae? 2. Describe what happens in detail when the hydrogen cloud begins to collapse under its own gravitational pull. 3. Describe what the main belt is and where it is located. 4. Why would impact craters on Mercury last a long time? 5. Describe one of the problems with the geocentric model. 6. Describe Retrograde motion. 7. List and describe two pieces of evidence that Galileo found to support the heliocentric model. 8. List and describe Kepler’s three laws of planetary motion. 9. All values for eccentricity fall between what 2 numbers? 10. List And describe one of Isaac Newton’s contributions to Astronomy. 11. If you tripled the distance between two masses, what happens to the force of gravity between them? 12. Define an Astronomical unit. 13. Which planet has a longer day then its year? 14. Which planet has the shortest day?