AST1002 Week 4
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This 8 page Class Notes was uploaded by Hugo Notetaker on Sunday September 18, 2016. The Class Notes belongs to AST1002 at University of Florida taught by Vicki Sarajedini in Fall 2016. Since its upload, it has received 6 views. For similar materials see Discovering the Universe in Astronomy at University of Florida.
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Date Created: 09/18/16
AST1002 Week 4 Chapter 5 Continued Crust 15 km thick (8 km under ocean 2050 km under continents) Mantle 3000 km thick (80% of planet volume) Core (3500 km outer core and 1300 km inner core) High central density suggests the core is mostly nickel and iron Density and temperature increase with depth Density “jumps” between mantle and core but smoothly increases between inner and outer core Accretion material comes together to make the planet 4.5 billion years ago (age of Sun). Earth was bombarded by interplanetary debris which made it hot. Differentiation different densities and compositions to the earth Earth was molten, allowing higherdensity material to sink to the core (this core material still has temperatures like that of the Sun!) Crustal Formation cooling and thickening of crust about 3.7 billion years ago The Surface of the Earth The Earth is still active today: earthquakes, volcanoes… Sites of activity outline surface plates plate tectonics Continental drift few cm/year Plates collide head on (mountains) or shear past (earthquakes) Some plates are separating (under Atlantic) new mantle material wells up between them What causes the forces that move the plates? Convection Each plate is crust + mantle Warm mantle rock (softened by high temps) moves up, cools off, moves down The Earth’s Magnetosphere – space influenced by Earth’s magnetic field Magnetic field lines run from the south to north magnetic poles Magnetic poles are close to (but not the same as) the axis poles The field is distorted by the solar wind Aurora Borealis Northern Lights – caused when the charged particles in the magnetic field and collide with Earth’s atmosphere near the poles What causes the Earth’s magnetic field? The rotation of the planet coupled with the electrically conducting liquid metal core = dynamo effect Lunar Surface lack of atmosphere and water preserves surface features Maria – mantle material “seas” darker areas resulting from earlier lava flow Basaltic, iron rich, high density (3300 kg/m3). Highlands – crust material elevated many km above maria Aluminum rich, low density (2900 kg/m3). Craters – the result of meteroid impacts pressure on the lunar surface heats the rock and deforms the ground an explosion caused by the impact pushes rock layers up and out an ejecta blanket surrounds the crater Craters can be up to 100km in diameter A new 10km crater is formed every 10 million years A new 1m crater is formed each month A new 1cm crater is formed every few minutes! The rate of cratering on the moon is determined from the known ages of the highland and maria regions. The Moon (and solar system?) experienced a sharp drop in the rate of meteoritic bombardment about 3.9 billion years ago (the end of the accretion epoch). The rate of cratering has been roughly constant since that time. Formation of the Moon theories 1. The moon was a sister planet formed together with Earth But, the moon is too different in density and composition 2. The moon formed somewhere else and was captured But, the moon is very similar to the Earth’s mantle Impact Theory Marssized body hit the molten Earth Parts of the mantle blew off and later formed the moon Earth had differentiated, so the mantle (from which the Moon formed) was already metal poor. Chapter 6 The Terrestrial Planets Mercury's Orbit and Rotation Astronomers initially thought Mercury's rotational and orbital periods were the same same side always facing the Sun Radar observations showed rotational period is 59 Earth days while MErcury's orbital period is 88 days Mercury is not tidally locked to the Sun Mercury's Atmosphere & Surface Almost nonexistent atmosphere due to high surface temperature and low escapes velocity drastic temperatures changes 700K (day) = 800 F 100K (night) = 280 F Chapter 6 Continued Venus Rotation direction is retrograde (opposite that of other terrestrial planets)! 243 day rotation period Axis is almost exactly perpendicular to orbit Why? Possibly hit by large body during formation altering spin direction Much more massive atmosphere than Earth’s Carbon dioxide (96.5%), Nitrogen (3.5%) No H20 the clouds are made of sulfuric acid Fast moving clouds in upper atmosphere but no wind at the surface – slow rotation 730K temperature on the surface (due to greenhouse effect) Elevated “continents” make up 8% of the surface (25% on Earth) Mostly rolling plains with some mountains (up to 14 km) No tectonics Buckled and fractured crust with numerous lava flows Volcanoes resurface the planet every ~300 million years Shield volcanoes are the most common (like Hawaiian Islands) A caldera (crater) is formed at the summit when the underlying lava withdraws Largest volcanic structures are called coronae upwelling in the mantle which causes the surface to bulge out not a fullfledged volcano. Usually surrounded by other volcanoes Venus is thought to still be volcanically active today Surfacing on Venus (the Soviets did) survived only an hour before burning up little evidence of erosion young surface rocks are basaltic and granite cloud cover makes Venus seem like a heavily overcast day on Earth all the time! Mars Slightly smaller than Earth Rotation period is 24.6 hours close to Earth Equator inclined at 24 degrees close to Earth Very little atmosphere 1/150 the pressure of Earth CO2 (95.3%),nitrogen (2.7%), argon, oxygen, CO, water vapor Two very small moons Spacecraft exploration of Mars 1965 – Mariner 4, 6 and 7 “fly by” Mars 1971 – Mariner 9 orbits and maps Mars in detail 1976 – Viking 1 lands on Mars 1997 Pathfinder and Sojourner rovers a highly successful mission which sent back lots of pictures of the Martian landscape (+ soil and atmosphere analyses) – revealed iron rich soil – Mars is “rusting” 2004 – rovers Opportunity and Spirit are currently studying evidence for water on Mars 2008 – Phoenix mission at north polar region Mars Surface Polar ice caps frozen CO2 Northern hemisphere rolling volcanic planes Like lunar maria but larger Few craters – young (3 billion yrs old) Southern hemisphere heavily cratered highlands Older (4 billion yrs old) Tharsis Bulge Roughly the size of North America, sits on the equator 10km high, less heavily cratered (i.e. young surface few billion yrs old) Valles Marineris extends onefifth of the way around the planet at the equator, up to 120 km across and 7 km deep, the Grand Canyon would fit into one of its side "tributary" cracks, probably produced from stretching and cracking when Tharsis bulge formed Volcanism on Mars Largest volcanoes in the solar system are here Shield volcanoes None are known to be currently active but eruptions occurred 100 million years ago Mars has a surface gravity only 40 percent that of Earth, and its volcanoes rise roughly 2.5 times as high because of this. Water on Mars? Yes but long ago About 4 billions years ago Mars had a thicker atmosphere, warmer surface, and likely also liquid water. Runoff channels Found in southern highlands Extensive river systems (like Earth) Carried water from highland to valleys Outflow channels Caused by flooding Found at the equator Formed about 3 billions year ago What happened to the water? Liquid water (from runoff channels) froze into permafrost (water ice just below surface) and polar caps about 4 billion years ago After ~1 billion years, volcanic activity heated the surface and melted permafrost Flash floods created outflow channels Volcanic activity slowed after that and the liquid water refroze Mars Global Surveyor in 2000 revealed “gullies” along the insides of craters evidence for more recent existence of liquid water? The Moons of Mars Mars has two very small moons discovered in 1877 Phobos – 28 x 20 km and Deimos – 16 x 10 km Less dense than our Moon or other terrestrial planets Likely to be captured asteroids Internal Structure of Terrestrial Planets Mercury Interior dominated by large iron core (high density and magnetic field present) Solid mantle prevents volcanoes and tectonics As core formed and cooled, shrinking caused the surface to contract (scarps,fissures, etc) Venus No magnetic field (slow rotation) surface of Venus resembles that of the young Earth, at an age of perhaps a billion years Never developed plate tectonics – possibly because of high surface temp and soft crust Mars Very weak magnetic field – non liquid core? largescale tectonic activity almost started but was stifled by rapidly cooling outer layers Chapter 7 The Jovian Planets Jupiter Named after the most powerful Roman God thirdbrightest object object in the night sky (after the moon and venus) Atmospheric cloud bands different than inner planets Many moons four largest called Galilean Moons Saturn Named after the father of Jupiter Almost twice Jupiter's distance from the Sun Similar banded atmosphere Uniform butterscotch hue Many moons Spectacular ring system Uranus Discovered by William Herschel in 1781 Named after father of Saturn Barely visible to naked eye Featureless atmosphere Deviations in the expected orbit of Uranus was another planet influencing its motion Yes, Neptune Neptune The other planet whose gravitational pull is influencing Uranus Mass and orbit were determined first (in 1845 by John Adams) In 1846 it was discovered by Johan Galle Cannot be seen with naked eye "Bluish" Jupiter atmosphere Space Craft Exploration of Jovian Planets Voyager 1 and 2 left Earth in 1977 Reached Jupiter in March and July of 1979 Used Jupiter's strong gravity to send them on to Saturn gravity assist Voyager 2 used Saturn's gravity to propel it to Uranus and then on to Neptune Studied planetary magnetic fields and analyzed multiwavelength radiation Both are now headed out into interstellar space! Galileo launched in 1989 and reached Jupiter in December 1995 Gravity assists from Venus and Earth Two components: atmospheric probe and orbiter Probe descended into Jupiter's atmosphere Orbiter went through moon system Cassini mission to Saturn arrived in 2004 Orbiter continues to orbit Saturn and its moons Huygens probe launched from the orbiter in 2005 to study Saturn's moon Titan Jovian Planet Properties Most of their mass is Hydrogen and Helium light elements = low densities High surface gravity of allows their atmospheres to retain these light elements Dense compact core at the center no solid surface gaseous atmosphere becomes denser (eventually liquid/semisolid) at core Differential Rotation outer regions rotate at a different rate than the inner regions Jovian planets Axis tilt and magnetic fields All Jovian planets have strong magnetic fields rapid rotation of liquid conductive cores or mantles Uranus has the most inclined rotational axis (extreme seasons) Jupiter's Atmosphere Two main features: colored bands and Great Red Spot molecular hydrogen 86% helium 14% small amounts of methane, ammonia, and water vapor Darker belts lie atop downward moving convective cells Lighter zones are above upward moving cells Belts are lowpressure, zones are high pressure As on Earth, wind moves from high to low Jupiter's rotation causes wind patterns to move East/West along equator Haze lies at the upper edge of the troposphere Thin layer of white ammonia clouds 125 150 K Colored clouds below that Warmer 200K Clouds are mostly droplets or crystals of ammonium hydrosulfide At deeper levels, clouds of water ice or water vapor The Galileo probe survived for about an hour before being crushed at this altitude Weather on Jupiter Main weather feature Great Red Spot swirling hurricane winds has lasted over 300 years why? There is no land to resist it Rotates with planet's interior the spot appears to be confined and powered by the zonal flow smaller storms look like white ovals Saturn's Atmosphere molecular hydrogen 92.4% helium 7.4% traces of methane and ammonia Overall temperature is cooler than Jupiter Cloud layer thickness is 3 times that of Jupiter (caused by lower surface gravity on Saturn) Thicker clouds result in less varied colors Computer enhanced image shows bands, oval storm systems, and turbulent flow patterns like those seen on Jupiter Atmosphere of Uranus and Neptune molecular hydrogen 84% helium 14% methane 2% (Uranus) 3% (Neptune) abundance of methane gives these planets their blue color Methane absorbs longer wavelength light (red) and reflects short wavelength light (blue) Uranus few clouds in the cold upper atmosphere featureless Upper layer of haze blocks out the lower, warmer clouds Neptune Upper atmosphere is slightly warmer than Uranus More visible features
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