Week Four Notes: Our Solar System, Formation of the Earth and Moon Our Solar System Solar System Solar system includes the Sun and any objects rotating around the Sun Sun Eight planets and their satellites Asteroids Comets Meteoroids The solar system Origin of the Solar System Nebular Theory Origin of the Solar System Nebular Theory The solar system condensed from a rotating cloud of hot gas (nebula) about 5 billion years ago. A thin disk of spinning gases formed. Gravity pulled the material inward. 99.85% of the nebula s material collected in the center to form a protostar (protosun) The remaining material formed a flat rotating disk. The center of the nebula heated, nuclear fusion began, and the sun was born. A temperature gradient formed within the disk around the sun, segregating elements. Metals and silicates close to the sun Gases further out Origin of the Solar System Nebular Theory (cont.) Material accreted into larger and larger bodies Accretion: colliding of material to make a larger mass. Planetesimals formed, followed by protoplanets, and planets Planetesimal: asteroid-sized celestial body that accumulated during the first stages of planetary formation Protoplanet: a developing planetary body that grows by the accretion of planetesimals Origin of the Solar System Nebular Theory (cont.) The composition of planetesimals was determined by the proximity to the protosun. Temperatures were highest closer to the protosun, and lower toward the outer edge of the nebular disk. Origin of the Solar System Nebular Theory (cont.) Planetesimals closer to the protosun were composed of materials with high melting temperatures (metals and rocky material) Planetesimals further from the protosun were composed mainly of ices Giant impacts with these materials continued for about a billion years, until most of the interplanetary debris was used Leftover material became asteroids and comets Nebular Hypothesis of Solar System Formation The Solar System The Solar System Our solar system includes the sun, its planets, and any other objects that orbit the Sun. Sun s planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune A planet s orbit lies in an orbital plane called the ecliptic Similar to a flat sheet of paper Overview of the solar system Two groups of planets occur in the solar system Terrestrial (Earth-like) planets Mercury through Mars 1
Small, dense, rocky Overview of the solar system Two groups of planets occur in the solar system Jovian (Jupiter-like) planets Jupiter through Neptune Large, low density, gaseous Massive Thick atmospheres composed of hydrogen, helium, methane, and ammonia The planets drawn to scale Planets in the Solar System Inner/Terrestrial (Earth-like) Planets Planets in the Solar System Outer/Jovian (Jupiter-like) Planets Planets in the Solar System The planets all orbit the sun in a counterclockwise direction when viewed from the north The inner planets are terrestrial - Mercury through Mars They are composed of silicate rocks and metals plus a thin atmosphere or none The outer planets are the Jovian planets - Jupiter to Neptune They are composed primarily of light elements like H & He and gases Often referred to as the gas giants All have ring systems Review of Density Density is the mass per unit of a substance. (D = m/v) It is the amount of stuff packed in a certain space. Which is more dense? Outgassing A Terrestrial Planet s General Internal Structure Formation of the planets Planets formed by accretion, and began to differentiate. Differentiation: separation or to become specialized (in this case by chemical separation) Denser elements and minerals sink toward the center and the less dense elements and minerals rise towards the surface. Different densities caused differentiation! As the planets formed, the materials that compose them separated Dense metallic elements (iron and nickel) sank toward their centers Lighter elements (silicate minerals, oxygen, hydrogen) migrated toward their surfaces Process called chemical differentiation Overview of the solar system All the planets travel in the same direction on slightly elliptical orbits. Because of gravity, objects closer to the Sun travel faster as they move around the Sun Example: Mercury has a high orbital speed of 48 km/sec; Pluto has a lower orbital speed of 5 km/sec. Solarbeat website of orbital frequencies: http://www.whitevinyldesign.com/solarbeat/ Atmospheres In the early history of the solar system, gravitational pull by the protoplanets sent planetesimals into very eccentric orbits Planets were bombarded by icy objects that originated from further out Planets will have an atmosphere if They are massive enough for gravity to keep the gases there They are far enough away from the Sun The terrestrial planets are small and have less gravitational pull to retain the gases 2
Have either small atmospheres or none Overview of the solar system Planets are composed of Gases Hydrogen Helium Rock Silicate minerals Metallic iron Ices Ammonia (NH 3 ) Methane (CH 4 ) Carbon dioxide (CO 2 ) Water (H 2 O) Planets: a brief tour Mercury Innermost and smallest planet No atmosphere Too hot and low escape velocity (due to less gravity) Cratered highlands Vast, smooth terrains associated with large impact basins where lava partially filled in the basins and lowlands Mercury Revolves around Sun quickly One year on Mercury is only 88 Earth-days Rotates very slowly on its axis One complete rotation takes two Mercury years! (One day on Mercury is 176 Earth-days) Mercury Has extreme temperatures (very hot and very cold) because it rotates so slow Side facing the Sun exceeds 427 C (800 F) Side away from Sun drops to -173 C (-280 F) A view of Mercury Venus Second to the Moon in brilliance in the night sky Similar to Earth in size and density Earth s sister planet Shrouded in thick clouds Impenetrable by visible light Atmosphere is 97 percent carbon dioxide Extreme greenhouse effect - 450 C (900 F) Surface atmospheric pressure is 90 times that of Earth s Slowest rotating planet One Venus day is 244 Earth Days; One Venus year is 225 Earth Days. Retrograde motion rotates opposite direction of other planets. Close encounters disrupt orbits. Either a near-collision with another planet, or if another star once passed too close to the system. Surface In 1970s, four Russian spacecraft landed, took images, and were crushed by atmospheric pressure within the hour. 3
Mapped by radar (unmanned Magellan mission) 80 percent of surface is subdued plains that are mantled by volcanic flows Atmospheric pressure prevents volcanism from being explosive Thousands of volcanic structures Low density of impact craters Thick atmosphere breaks up and incinerates debris Lava flows cover up craters Computer generated view of Venus Planet Earth Planet Earth The Earth is about 150,000,000 km from the sun (about 93,000,000 miles) 8 minutes travel time for light Earth dimensions 12,900 km in diameter (8062 miles) 40,250 km in circumference (25,000 miles) The shape is an oblate spheroid Polar diameter is about 42 km (26 miles) less than the equatorial diameter Oblate Spheroid Formation of Earth Accretion, differentiation, and outgassing Outgassing formed first clouds After millions of years, the clouds cooled enough to create rain Cooled the surface and eroded the first rocks Rains may have lasted as long as 25 million years. Water may have covered Earth s surface for 200 m.y.! Mars Called the Red Planet due to iron oxide (rust) Thin atmosphere 1 percent as dense as Earth s Primarily carbon dioxide Extensive dust storms with winds up to 270 kilometers (170 miles) per hour Two moons (captured asteroids) Tectonically dead Numerous large volcanoes largest is Olympus Mons Largest volcano in the solar system Formed from a mantle plume, but surface not moving, so large volcanoes form Less-abundant impact craters Several canyons Valles Marineras the largest canyon Formed from an are that bulged upward (Tharsis Bulge) forming cracks due to the uplift Olympus Mons, an inactive shield volcano on Mars size of Arizona! Gullies and canyons on Mars Water on Mars! (But only frozen today) Polar caps of water ice, covered by a thin layer of frozen carbon dioxide Probably permafrost (frozen, icy soil) beneath surface Surface has stream drainage patterns and flood channels Surface material collapses as the subsurface ice melts 4
True drainages Has layers of sedimentary rocks, playas, lake beds, and minerals that only form in the presence of water Hydrated sulfates hematite Jupiter Largest planet Very massive 2.5 times more massive than combined mass of the planets, satellites, and asteroids If it had been about 80 times larger, it would have been a small star Rapid rotation Slightly less than 10 hours Slightly bulged equatorial region Most moons at least 63 moons Structure of Jupiter s atmosphere Great Red Spot In planet s southern hemisphere Counterclockwise rotating storm Banded, multicolored, atmosphere appearance due to cloud layers Jupiter is shrinking a few cm/year This contraction generates heat, which drives convection of the atmosphere light colored regions are where warm material is ascending and dark bands are where cool material is descending and again warming Structure Surface thought to be a gigantic ocean of liquid hydrogen Rocky and metallic material probably exists in a central core The Galilean moons Saturn Saturn Similar to Jupiter in its Atmosphere Composition Internal structure Rings Small particles of mostly ice and some rock Origin is still debated debris ejected from moons From nebula From asteroid or moon that was pulled apart Foreign body collided with a moon Uranus Bluish color Methane in the atmosphere Rotates on its side Huge impact early in its evolution Rings Neptune Bluish color Methane in the atmosphere 5
One of the windiest places in the solar system Wind speed 2,400 km/hr (1,500 miles/hr) Great Dark Spot Shorter-lived than Great Red Spot-only a few years Thirteen satellites Rings Smaller members of the solar system Asteroids Comets Meterorids Dwarf Planets Asteroids and meteoroids Composed of rock and/or metallic material Asteroids are larger than 100 m Meteoroids are smaller than 100 m Most lie in the asteroid belt between Mars and Jupiter Some have very eccentric orbits Leftover material from the formation of the solar system The orbits of most asteroids lie between Mars and Jupiter When objects are coming towards Earth Called meteors when they enter Earth s atmosphere A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet s path meteorites when they are found on Earth Comets Also leftover material from the solar nebula Often compared to large, dirty snowballs Composition Frozen gases Rocky and metallic materials Most comets originate in either the Kuiper belt or the Oort cloud Kuiper belt: a disk-shaped region past Neptune where most short period comets originate Similar to the asteroid belt, but made of icy bodies Oort cloud: a spherical shell of comets greater than 10,000 AU away Orientation of a comet s tail as it orbits the Sun Dwarf planets New class of objects (2006) Dwarf planet: a body that orbits the Sun that is massive enough for its shape to be controlled by gravity (oblate spheroid), but that, unlike a planet, has not cleared its orbital region of other objects Pluto is one of possibly hundreds in this new category 5 currently identified Pluto If you added up the mass of all the other objects in Pluto s orbit, Pluto s mass would only be a tiny fraction of that total. It would only be 0.07 times as massive as everything else. 6
Size 1/5 the size of Earth; less than ½ the size of Mercury. 7 moons in the solar system are larger than Pluto (including ours) Located in the Kuiper belt a band of icy objects found beyond the orbit of Neptune 50 70% rock and 30 50% ice named after a god, not a dog Roman god of the underworld Name suggested by Venetia Burney, an 11-year old girl in oxford, England. She thought it was a good name for such a cold, dark world Pluto s orbit is highly inclined, traveling at an angle of 17 from the ecliptic Origin of the Moon - Giant Impact Theory See SwRI UCSC animation: http://www.swri.org/press/impact.htm Where Did the Moon Come From Video : https://www.youtube.com/watch?v=c0fce4h0dro Origin of the Moon - Giant Impact Theory A Mars-sized object makes an oblique hit on the Earth about 4.5 billion years ago. This is about the largest object that could hit without shattering the Earth Earth was completely disrupted with penetration reaching the core. Most ejected material would come from the mantles of the 2 objects Vast amount of material was ejected into Earth s orbit. Material coalesced to form the Moon Moon has a low density, large mantle, and small iron-rich core. Earth s Moon General characteristics Diameter of 3,475 kilometers (2,150 miles) is unusually large compared to its parent planet Density 3.3 times that of water Comparable to Earth s mantle rocks Earth s Moon Gravitational attraction is 1/6 of Earth s Person weighing 150 lbs. on Earth would weigh 25 pounds on the Moon (mass stays the same) Jump 6x higher! No atmosphere Small mass and therefore low gravity Tectonics no longer active Surface is bombarded by micrometeorites from space which gradually makes the landscape smooth Lunar Surface Two types of terrain Dark lowlands (maria) and bright, highly cratered highlands (lunar highlands) Maria Latin for seas Dark smooth lowland plains of basaltic lava Impact crater later fills with lava, flooding the surface Younger than highlands, because the lava flows are less cratered 7
Lunar Highlands Bright, densely cratered regions Make up most of the Moon s surface Make up most of the far side or dark side of the Moon Older than maria Craters Most obvious features of the lunar surface Younger craters still have a prominent ejecta blanket and rays that cover older craters Lack of weathering, erosion, and tectonics so craters still persist. Lack of atmosphere, so micrometeorites bombard the surface Lunar regolith Regolith layer of rock and mineral fragments. NOT SOIL!!! Soil = minerals + organic matter + water + air Covers all lunar terrains Composed of Igneous rocks Breccia Glass beads Fine lunar dust Does the moon have soil? No, it has a regolith derived from meteorite impacts. Missing water, air, and organic matter! Motions of the Earth-Moon system Always see the same side Because its period of rotation on its axis (27 1/3 days) equals its period of revolution around Earth (27 1/3 days), we always see the same side of the moon Phases of the Moon When viewed from above the North Pole, the Moon orbits Earth in a counterclockwise (eastward) direction The relative positions of the Sun, Earth, and Moon constantly change Lunar phases are a consequence of the motion of the Moon and the sunlight that is reflected from its surface At all times, half of the Moon is lit by the Sun. The other half of the Moon facing away from the Sun is in darkness. As the Moon orbits around the Earth we can see more and more of its lit side. This process slowly changes. These changes are called the phases of the Moon. Eclipses An eclipse occurs when one object gets in between you and another object and blocks your view. Example: An eclipse of the board From Earth, we routinely experience two kinds of eclipses: an eclipse of the Moon and an eclipse of the Sun. Lunar and Solar Eclipses Eclipses Simply shadow effects Two types of eclipses Solar eclipse 8
Lunar eclipse Solar eclipse Moon moves in a line directly between Earth and the Sun Can only occur during the new-moon phase Lunar eclipse Moon moves within the shadow of Earth Only occurs during the full-moon phase Why don t we have an eclipse twice every month? Because the Moon s orbit is inclined about 5 degrees to the plane of the ecliptic For any eclipse to take place, the Moon must be in the plane of the ecliptic at the time of new- or full-moon phase During most of new and full Moons the Moon is above or below the plane, and no eclipse can occur The usual number of eclipses is four per year Earth-Moon months (Moonths) Synodic month Cycle of the phases Takes 29 1/2 days Sidereal month True (REAL) period of the Moon s revolution around Earth Takes 27 1/3 days The difference of two days between the synodic and sidereal cycles is due to the Earth-Moon system also moving in an orbit around the Sun 9