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Pg 6 of Space Notes Solar Nebula Model Original Cloud is large and spread out with little rotation The cloud heats up and spins faster and faster as it contracts (centripetal force) This results in a spinning, flattened disk, with mass concentrated near the center Building The Planets • Condensation: Sowing the Seeds of Planets – Condensation is the formation of solid or liquid particles from a cloud of gas. – We refer to such solid particles as condensates. The Ingredients of the Solar Nebula Fell Into Four Categories Based on Their Condensation Temperatures: • Metals • Rocks • Hydrogen compounds • Light gases Accretion: Assembling the Planetesimals (baby planets) • The process of growing by colliding and sticking is called accretion. • The growing objects that formed by accretion are called planetesimals, which means “pieces of planets”. Early in the accretion process, there are many Moon sized planetesimals on crisscrossing orbits As time passes, a few planetesimals grow larger by accretion while others collide and are destroyed Only the largest planetesimals avoid being destroyed. These bodies will become the planets of this newly formed solar system Nebular Capture: Making the Jovian Planets • Large icy planetesimals of the outer solar system act as seeds for capturing large amounts of hydrogen and helium gas. This is called nebular capture. • This explains the large sizes and low densities of the Jovian planets. • Nebular capture also explains the formation of the diverse satellite systems of the jovian planets. The Solar Wind: Clearing Away the Nebula • The remaining gas of the solar nebula was blown into interstellar space by the solar wind (a flow of charged particles ejected by the Sun in all directions.) Leftover Planetesimals • Origin of Asteroids and Comets: • The strong wind from the young Sun cleared excess gas from the solar nebula, but many planetesimals remained scattered between the newly formed planets. • These leftovers became the comets and asteroids. Your Parents’ Solar System st 21 Century Solar System The 21st Century Solar System Sun Terrestrial Planets Asteroid Belt Jovian Planets Kuiper Belt Oort Cloud The Solar System: List of Ingredients Ingredient Sun Jupiter Other planets Everything else Percent of total mass 99.8% 0.1% 0.05% 0.05% The Sun • A middle-aged, average star: – Mostly Hydrogen & Helium – 99.8% of the Solar System – ~4.6 billion years old • Shines because it is hot: – Surface Temp ~6000 C – Mostly Visible, UV & IR light • Kept hot by nuclear fusion in its core: – Builds Helium from Hydrogen fusion. – Will shine for ~12 billion years The Sun dominates the Solar System Terrestrial Planets • Mercury, Venus, Earth & Mars – “Earth-Like” Rocky Planets – Largest is Earth – Only in the inner solar system (0.4 to 1.5 AU) • Rocky Planets: – – – – Solid Surfaces Mostly Silicates and Iron High Density: (rock & metal) Earth, Venus, & Mars have atmospheres The Terrestrial Planets Mercury Venus (0.055 M) (0.82 M) Earth (1 M) Mars (0.11 M) MERCURY Mercury, the planet nearest the Sun, is the smallest planet in our solar system. It is only slightly larger than the Earth's moon. The surface is covered with craters. This tiny planet does not have any rings or moons. evidence of craters VENUS impact craters lava flows Venus is one of the brightest objects in our sky, so it is clearly visible to the naked eye. It can be tricky to spot because it is always near the Sun. It is the solar system's brightest planet -yellow clouds of sulfuric acid reflect the sun's light brightly. Venus is sometimes referred to as Earth's “sister”, due to the two planets similarity in size, composition and gravity. Lots of Greenhouse Gases! Making the planet very hot! MARS Mars is very bright, which makes it easy to spot in the night sky. It was named after the Roman god of war because its reddish color reminded the people of blood. Mars is known as the “Red Planet” due to the high prevalence of iron oxide on its surface. Olympus Mons is the largest volcano in our solar system! Although people have never landed on Mars, Martian crater we have sent robotic explorers there. The Jovian Planets • Jupiter, Saturn, Uranus & Neptune – – – – Largest Planets: at least 15 times mass of Earth. Only in the outer solar system (5 to 30 AU) No solid surfaces (mostly atmosphere) Low density • Gas Giants: (Jupiter & Saturn) – Thick H/He atmosphere, liquid hydrogen mantle, ice core • Ice Giants: (Uranus & Neptune) – Ice/rock core & mantle, thin H/He atmosphere The Jovian Planets Jupiter (318 M) Saturn (95 M) Uranus Neptune (15 M) (17 M) ASTEROID BELT Most asteroids can be found in the Asteroid Belt, which is located between Mars and Jupiter. Asteroids are rocky and metallic objects that orbit the Sun, but are too small to be considered planets. They are known as dwarf planets. Asteroids range in size from Ceres, which has a diameter of about 1000 km, down to the size of pebbles. JUPITER Jupiter, the fifth planet from the Sun, is the largest planet in our solar system. Jupiter is so big that over 1,000 planets the size of Earth could fit into it. It has over 60 moons and 2 rings. The “Great Red Sp Is actually a huge Storm system! Here are a few of Jupiter’s moons SATURN Saturn, the sixth planet from the Sun, is the second largest planet in our solar system. It is often called the ringed planet because many rings of dust and rocks surround it. Saturn also has over 31 moons. Saturn is the only planet in the Solar System with a density lower than water. Some of Saturn’s rings Saturn with some of its moons URANUS Uranus is a very unusual planet because it sits on its side with north and south poles sticking out the sides. It rotates around this axis, making it look like a ball rolling around in a circle around the Sun. Black rings NEPTUNE Neptune, usually the eighth planet from the Sun, is a very cold place. Occasionally, Pluto crosses Neptune’s orbit and becomes the eight planet. Its bluish color comes from its atmosphere of methane gas. Tiny Dark Moon Dwarf Planets • Defined by the IAU in 2006 • Dwarf Planets: – Ceres: first of the Asteroids, discovered in 1801 – Pluto: trans-Neptunian object discovered in 1930 – Eris: trans-Neptunian object discovered in 2005 – Haumea (trans-Neptunian, suspected) – Makemake (trans-Neptunian, suspected) Dwarf Planets The Giant Moons • Moon: any natural satellite orbiting a planet or dwarf planet • Giant Moons: – – – – Earth: The Moon (Luna) Jupiter: Io, Europa, Ganymede, & Callisto Saturn: Titan Neptune: Triton • Many smaller moons, both rocky & icy. • Only Mercury & Venus have no moons. The Giant Moons Mimas Mercury Iapetus Miranda Proteus Tethys Dione Umbriel Europa Moon Pallas Ariel Io Hygeia Triton Titan Ganymede Vesta Oberon Callisto Ceres Rhea Titania Enceladus Pluto Charon Kuiper Belt • Class of icy bodies orbiting beyond Neptune. – Found only in the outer Solar System (>30AU) – Densities of 1.2 to 2 g/cc (mostly ices) • Examples: – – – – Pluto & Eris (icy dwarf planets) Kuiper Belt Objects (30-50AU) Charon, Pluto’s large moon Sedna & Quaor: distant large icy bodies Kuiper Belt Oort Cloud • Spherical cloud of comets. – Extends out to almost 50,000 AU (1 light-year) – May contain trillions of comets – The outer edge is the farthest reach of the Sun’s gravitational pull. – There are no confirmed observations – its existence is theoretical only. Oort Cloud The Leftovers (small bodies) • Asteroids: – Made of rock & metal (density 2-3 g/cc) – Sizes: Few 100km to large boulders – Most are found in the Main Belt (2.1-3.2 AU) • Meteoroids: – Bits of rock and metal – Sizes: grains of sand to boulders • Comets: – Composite rock & ice “dirty snowballs” – Longs tails of gas & dust are swept off them when they pass near the Sun. Asteroids 253 Mathilde 951 Gaspra 243 Ida Meteor burning up in the atmosphere.