10 Solar System - ASTR 122 Feb 19 2013 Lecture 10 The Solar System Topics for Today What are the major features of our Solar System How do we define a

10 Solar System - ASTR 122 Feb 19 2013 Lecture 10 The Solar...

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Unformatted text preview: ASTR 122 -­‐ Feb. 19, 2013 Lecture 10: The Solar System ‣ Topics for Today ‣ What are the major features of our Solar System? ‣ How do we define a “planet?” ‣ Reminders ‣ Homework 5 due tonight by 11:59pm ‣ Night Observing 7-9pm, M-Th this week! ‣ Reading for next class ‣ Sections Thursday, February 28, 13 9.1-9.3: The Sun 1 A survey of the solar system Our Solar System Thursday, February 28, 13 Today we know Solar system has: 1 star, 8 planets, 5 dwarf planets, 139+ moons, countless small solar system bodies This image shows an artist's impression of our solar system with separate representations of scale and size. The planets and dwarf planet Pluto are shown in their correct order of distance from the sun, their correct relative sizes (above) and their correct relative orbital distances (below). The sizes of the bodies are greatly exaggerated relative to the orbital distances. First lets take a look at some overall features of our solar system 2 Windows to the Universe Original The Sun Thursday, February 28, 13 The Sun is a huge, glowing ball of mostly hydrogen and helium gas at the center of our solar system. The sun provides light, heat, and other energy to Earth. Earth travels around the sun at an average distance of about 149,600,000 kilometers (92 million miles). The sun's diameter is about 1.4 million km (864,000 miles), approximately 109 times Earth's diameter. The Sun has 99.8% of the mass in the entire solar system! Its mass is roughly 2 X 1027 tons. This number would be written out as a 2 followed by 27 zeros - or about 333,000 times as massive as Earth. 3 A Journey Through Our Solar System The solar system contains lots of empty space A portion of the Voyage scale model of the Solar System on the National Mall in Washington, DC, is shown in the photograph. The real Solar System is exactly 10 billion times larger than the model. Voyage stretches from the east side of the National Air and Space Museum to the Smithsonian Castle, as seen on the map below. The planets depicted on the cover of this brochure are the same size as Voyage’s model worlds. you had reached the California coast. The Sun and Proxima Centauri are just two stars in our home ‘city of stars’—the Milky Way galaxy. The Milky Way, an insignificant plot of real estate in the greater universe, contains enough stars to give 50 to every human being on Earth. How insignificant is the Milky Way? It is only one of over 100,000,000,000 galaxies in the observable universe. Imagine leaving the grapefruit-sized Sun walking westward toward the Washington Monument. After walking just 50 feet (15 m) you encounter Earth, home of the human race, and smaller than the head of a pin. The entire orbit of the Moon fits comfortably in the palm of your hand. The 50-foot distance between the Earth and Sun represents 17 years of travel at the speed of a commercial jet. Light, the fastest thing in the universe, can circle the Earth 7.5 times in one second, traveling 40,000 times faster than the space shuttle. The speed of light on the scale of Voyage is 1 inch per second (2.5 cm/sec), about the speed of a fast ant. Leaving the model Sun an ant would arrive at the model Earth in eight minutes, Pluto in 6 hours, and a model Proxima Centauri in California after 4.5 years. Put another way—exploring just the space between the Sun and nearest star to the Sun at the fantastic speed of light, would be like exploring the continental United States as a colony of ants. ‣ On The Voyage exhibition is a one to 10-billion scale model of the Solar System stretching 2,000 feet (600 meters), and containing ten 8.5-foot high aluminum stanchions locating the Sun and nine planets, and three smaller stanchions that provide entry points to the exhibition, and address asteroids and comets. Voyage reflects a seamless fusion of sculpture and science education, conveying an aesthetic beauty worthy of placement on the National Mall in Washington, DC, as required by the approving bodies—the U.S. Commission of Fine Arts, and the National Capital Planning Commission. The imagery and text provide a compelling up-close view of the planets and moons, in stark contrast to the 3-D models that speak to the powerful reality of tiny worlds in a vast space. Voyage transforms visitors into cosmic explorers and turns a leisurely 20-minute walk into a fascinating journey through the Solar System. a 1-to-10 billion scale: → a large cantelope (14 cm across) ‣ Earth → a ball point (1.3 mm), 15 m away ‣ Jupiter → a fingertip (14 mm), 78 m away ‣ Pluto → a dust speck (0.2 mm), 590 m away After a comfortable 20-minute walk, stopping along the way to visit a number of other worlds, you arrive at the Smithsonian Castle Building, 6.5 football fields west of the model Sun (2000 ft or 600 m). Here, just visible, is tiny Pluto—far smaller than the head of a pin. Looking back at the model Sun, across over 6 football fields of empty space, you realize that Earth is no more than a small speck of dust orbiting close to the Sun. How does the human race even know Pluto exists? If you could continue your walk westward you wouldn’t find the nearest star to our Sun—Proxima Centauri—until Smithsonian Exhibitology © 2006 ‣ Sun Represented as a striking gold-anodized metal sphere, the Sun—our star— can be seen by visitors in the exhibition’s outer Solar System. All planets and moons with a diameter greater than 1,000 km [24 worlds] are depicted to scale as 3-dimensional crystalline spheres laser-sculpted inside solid glass. The ring systems of the outer planets are also accurately depicted, including their orientation in space. Full color imagery, much of which was commissioned for the exhibition, is found on porcelain enamel storyboards at each stanchion. Thoughtprovoking text transports the visitor by reshaping their Earthly experiences into those reflective of other worlds. This is the story of our existence—a race of explorers, 6 billion tiny souls strong. It is a story that ignites wonder about the universe, and a sense of pride in our ability to reveal its nature through both human imagination and ingenuity. It is a story that humbles us, and brings a sense of humility to our lives. Images courtesy Smithsonian Exhibitology © 2006 VOYAGE Development and installation of the exhibition in Washington, DC, was a joint project of Challenger Center for Space Science Education, the Smithsonian Institution, and NASA. Replication and installation of the Voyage exhibition at sites nationally and internationally is a program of the National Center for Earth and Space Science Education (NCESSE; ), Universities Space Research Association. Voyage was designed by Vincent Ciulla Design ( ). The Voyage Exhibition: A 1-to-10 billion scale model of the solar system on the National Mall Thursday, February 28, 13 4 Use this slide/tool to introduce the Voyage scale (Voyage is the name of the model solar system using this scale on the National Mall in Washington, DC). • Voyage shows a straight line, but remember that planets orbit. In class, put the grapefruit for the Sun on a table, then walk 15 meters to Earth position, and ask students to imagine it going around Sun once a year. • A major lesson from all this is that the solar system is almost entirely made of nearly empty space (that’s why they call it “space”!). Planets show common direcFons of moFon The planets orbit the Sun all in the same direction Thursday, February 28, 13 Planet orbits: Go around in the same direction. Orbits are very close to circular Rotations of the Sun and most planets are also in this same direction Orbits of dwarf planets and small solar system bodies can be very eccentric Exceptions: Rotation - Venus, Uranus, Pluto Circular orbits - Mercury, Pluto (and many objects near Pluto) all have very eccentric orbits 5 Planet orbits lie close to a common plane The solar system is basically ‘flat’ and disk-shaped Thursday, February 28, 13 The planets revolve around the sun in orbits that lie close to a common plane. The orbit of Mercury, the planet closest to the sun, is tipped 7° to Earth’s orbit. The rest of the planets’ orbital planes are inclined by no more than 3.4°. Orbits of dwarf planets (like Pluto) and small solar system bodies can be very inclined 6 Two Basic Types of Planets Terrestrial Planets Jovian Planets Closer to the Sun, closer together Smaller sizes and masses Higher densities Farther from the Sun, farther apart Larger sizes and masses Lower densities Compositions: mostly rock and metal Compositions: hydrogen, helium, “ices” No solid surfaces Colder temperatures at cloud-tops Many moons All have ring systems Solid surfaces Warmer surfaces Few moons No rings Thursday, February 28, 13 Terrestrials (or rocky planets): Closest to the Sun, Largely composed of rock Mercury, Venus, Earth and Mars Jovians (or gas giants): Further from the Sun, Planets largely made up of gaseous material, Much more massive than terrestrials, All have many moons & rings Jupiter, Saturn, Uranus, and Neptune 7 The Terrestrials (& the Moon) Mercury Mars Venus Earth Sizes to scale Small size Low mass Higher density Mostly rock Few, if any moons, no rings Thursday, February 28, 13 • • • • • Mercury is a small, airless, extensively cratered world. It is only 30% larger in diameter than the Moon. Venus is nearly the same size as Earth. Hotter than Mercury! Venus’s high temperatures are due to its extremely thick CO2 atmosphere. It is shrouded by a perpetual cloud cover that hides its surface from view. Only with radar can we observe its surface. (click to reveal a radar image of Venus’ surface) The Earth is unique in many ways. It has an abundance of liquid water, a thin but not too thin atmosphere, an active surface, and life. The Moon’s airless, dry surface is covered with plains and craters. Earth is the only terrestrial planet with a large moon. Mercury & Venus have no moons. Mars’ moons are small captured asteroids. Mars has captivated the popular imagination like no other planet, showing evidence of having had liquid water on its surface for extended periods. Mars has the most Earth-like surface in the solar system. But due to it’s thin CO2 atmosphere and being 50% farther from the Sun than Earth, Mars’ surface is freezing cold. Images: NASA, Wikimedia Commons Moon 8 The Jovians Earth (for reference) Uranus Neptune Jupiter Saturn Bigger & more massive ‣ Lower density, different composition ‣ Rapid rotation ‣ Rings, numerous moons ‣ Thursday, February 28, 13 More massive, but less dense, than the Terrestrial planets Accumulated large amounts of hydrogen and helium Thick, high pressure atmospheres, of hydrogen, helium, methane, ammonia, (some evidence for water!) • Jupiter is the most massive planet in our solar system. The planet's swirling cloud stripes are punctuated by massive storms such as the Great Red Spot, which has raged for hundreds of years. • Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. All four gas giant planets have rings -made of chunks of ice and rock -- but none are as spectacular or as complicated as Saturn's. • Uranus is the only giant planet whose equator is nearly at right angles to its orbit. Methane gives Uranus its blue tint. • Dark, cold and whipped by supersonic winds, Neptune is the last of the hydrogen and helium gas giants in our solar system. More than 30 times as far from the sun as Earth, the planet takes almost 165 Earth years to orbit our sun. 9 The Dwarf Planets Images courtesy of NASA, ESA, JPL, and A. Feild (STScI). Moon Sizes to scale (with Earth & Moon for reference) Thursday, February 28, 13 The dwarf planets are much smaller than any terrestrial planet or even Earth’s moon. Eris, Pluto,Makemake, Haumea are beyond Neptune, Ceres is between Mars & Jupiter Eris, Pluto, Makemake, Haumea are composed largely of ices, Ceres largely of rock Makemake - formerly nicknamed Easterbunny, now named for an Easter Island deity. Huamea - formerly nicknamed Santa, now named for a Hawaiian deity. 10 Thursday, February 28, 13 There are over 160 known moons in the solar system (and counting) Among the terrestrials, only Earth & Mars have moons (and Mars’ are tiny) Jupiter & Saturn ~60 each, mostly small Uranus & Neptune - 1-2 dozen each, so far Pluto - 4 moons so far Eris - 1 moon 11 Small Solar System Objects: Asteroids airless worlds that orbit the sun ‣ Too small to be called planets. NASA NASA ‣ Rocky, Asteroid Eros Most asteroids lie in a belt between Jupiter and Mars Thursday, February 28, 13 The solar system is littered with space debris. Asteroids are rocky, airless worlds that orbit our sun, but are too small to be called planets. Tens of thousands of these "minor planets" are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called Near-Earth Objects 12 Small Solar System Objects: Comets are “dirty snowballs” of ices, rock, and dust ‣ A few to tens of km across ‣ Most orbit beyond Neptune ‣ When near the Sun, exhibit tails up to millions of km long! ESA ‣ Comets Comet C/2002 V1 (NEAT) Thursday, February 28, 13 Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the sun for millions of kilometers. 13 Thought QuesFon The Venn diagram shown below describes the characteristics of Terrestrial and Jovian planets. At which location would the characteristic large masses best be placed? Thursday, February 28, 13 Answer B 14 Thought QuesFon The Venn diagram shown below describes the characteristics of Terrestrial and Jovian planets. At which location would the characteristic high densities best be placed? Thursday, February 28, 13 Answer A 15 Thought QuesFon The Venn diagram shown below describes the characteristics of Terrestrial and Jovian planets. At which location would the characteristic nearly coplanar orbits best be placed? Thursday, February 28, 13 coplanar: all the orbits lie in the same plane. Answer C 16 i>clicker poll Should Pluto be considered a planet? A. B. C. D. E. Thursday, February 28, 13 Definitely yes Probably yes I don’t know Probably no Definitely no 17 What is a planet? The solar system’s planets and dwarf planets Thursday, February 28, 13 18 For about 70 years there were 9 planets: 4 rocky, 4 gas giants, 1 “misfit” In 2006, the IAU passed a resolution that defined planet and established a new category, dwarf planet. Eris, Ceres, Pluto, and two more recently discovered objects named Haumea and Makemake, are the dwarf planets recognized by the IAU. Previous definiFons of a planet ‣ Our ancestors noted five planets whose positions relative to the stars slowly changed over time ‣ Mercury, Venus, Mars, Jupiter, Saturn ‣ In 1543, Copernicus proposed a Suncentered model of the Universe ‣ The planets (now including Earth) are bodies that orbit the Sun Thursday, February 28, 13 NOTE - Earth is not a planet by the ancient definition. Copernicus knew of 6 planets: Mercury, Venus, Earth, Mars, Jupiter & Saturn 19 Discoveries of new planets Uranus Neptune Pluto NASA ‣ In 1781, William Herschel discovered the first new planet since ancient times, Uranus. ‣ Neptune was discovered in 1845 ‣ In 1930, Pluto was discovered by Clyde Tombaugh Thursday, February 28, 13 20 Why did Pluto get “demoted?” Pluto’s status as a planet was questioned due to its small size and crowded orbit Thursday, February 28, 13 Upon its discovery, Pluto was considered the solar system's ninth planet Starting the in 1970s, Pluto’s status as a planet began to be questioned Two reasons: Small size Crowded orbit 21 Pluto is smaller than many moons in the Solar System! Callisto Ganymede Io Titan Earth’s Moon Triton Europa Pluto Thursday, February 28, 13 Pluto is smaller than many moons in the solar system 22 Pluto’s orbit lies in a crowded region -­‐ the Kuiper Belt Pluto and Eris can be found in the Kuiper Belt Thursday, February 28, 13 23 Since 1992, astronomers have discovered roughly a thousand small, dark, icy bodies orbiting in the outer fringes of the solar system beyond Neptune. This collection of objects is called the Kuiper belt. There are probably 100 million bodies larger than 1 km in the Kuiper belt. Some comets originate in the Kuiper belt. P5 P4 Thursday, February 28, 13 Pluto’s size is typical of the largest trans-neptunian objects. 24 “Planet” redefined in 2006 Planet Dwarf Planet Is in orbit around the Sun (i.e., it is not a moon) Has sufficient mass to assume a nearly round shape Has cleared the neighborhood around its orbit Has not cleared the neighborhood around its orbit ✔ ✔ ✔ ✔ ✔ ✔ This table illustrates the defining characteristics of planets and dwarf planets, following the 2006 re-definition of a “planet” Thursday, February 28, 13 This table illustrates the defining characteristics of planets and dwarf planets. The key difference between planets and dwarf planets is “clearing the neighborhood”. What does that mean? 25 Clearing the neighborhood Dwarf planets have not “cleared the neighborhood” of smaller objects Thursday, February 28, 13 To distinguish a planet from a dwarf planet, a planet must be massive enough to clear smaller objects – like asteroids – from their own orbit. The gravity of the planet would pull in smaller objects which would become part of the new planet. The dwarf planets are not massive enough to do this. Ceres is found a region of small rocky bodies between the orbits of Mars and Jupiter known as the Asteroid Belt. Pluto, Huamea, Makemake, and Eris are in a region of small icy bodies beyond Neptune known as the Kuiper Belt. 26 Pluto is not a dog... ...its a dwarf! Thursday, February 28, 13 Pluto is not a dog... its a dwarf! Has a planet ever been demoted before? YES! 27 Ceres, Another Former Planet NASA NASA ‣ Ceres was considered a planet for 50 years after its discovery in 1801 ‣ Reclassified as an “asteroid” after similar bodies were found between Mars & Jupiter ‣ Now, also a dwarf planet Thursday, February 28, 13 On january 1 1801, Ceres was discovered (after uranus, before neptune and pluto). It was celebrated as a “new planet” between Mars & Jupiter Ceres was listed as a planet in astronomy books and tables for about half a century Ceres turned out to be disappointingly small, only 1000 km across When other, similar but smaller, objects were found in the same area between Mars and Jupiter, Ceres was demoted from planethood and re-designated an “Asteroid” (small rocky body orbiting the Sun), of which it is the largest of millions. 28 i>clicker poll Should Pluto be considered a planet? A. B. C. D. E. Thursday, February 28, 13 Definitely yes Probably yes I don’t know Probably no Definitely no 29 Name Pluto’s Moons! ‣ Two new moons of Pluto were discovered in 2011-2012 ‣ Currently designated P4 & P5 ‣ Pluto now has 5 known moons ‣ You can vote to name these moons at ‣ Voting closes Monday, Feb. 25th at 11am, CST Thursday, February 28, 13 30 Key Ideas ‣ Planets orbit Sun in the same direction and in nearly the same plane ‣ Two main planet types: Terrestrial and Jovian ‣ Smaller bodies: Dwarf planets, asteroids, comets, moons ‣ The definition of a planet ‣ is in orbit around the Sun ‣ has sufficient mass so that it assumes a nearly round shape ‣ has cleared the neighborhood around its orbit ‣ Dwarf planets satisfy the first two, but not the third Thursday, February 28, 13 31 ...
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