ASTR 151 Unit 2 Study Guide
ASTR 151 Unit 2 Study Guide ASTR 151 001
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ASTR 151 001
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This 16 page Study Guide was uploaded by Wesley Fowler on Tuesday April 5, 2016. The Study Guide belongs to ASTR 151 001 at a university taught by Dr. Sean Lindsay in Spring 2016. Since its upload, it has received 63 views.
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Date Created: 04/05/16
Wesley Fowler ASTR Chapter 4 The Solar System The Sun makes up 99.8% of the Solar System’s mass The Solar System is primarily empty space! It has a range of 30.1 AU from the Sun to Uranus Mercury-Venus-Earth-Mars-Jupiter-Saturn-Uranus-Neptune 5 Dwarf Planets: Ceres (Asteroid belt), [Pluto, Haumea, Makemake, Eris (Kuiper Belt Objects)] 181 Moons Estimated millions of Asteroids (600,000 discovered) Estimated billions of Comets (4,000 discovered) The Kuiper Belt: The outer region beyond Neptune, filled with meteoroids, interplanetary dust, and pervasive solar wind. 30-2,000AU from Sun is the Kuiper Belt. 0-30: Planetary Realm 30-2,000: Kuiper Belt + Scattered Disk 2,000-20,000: Inner Oort Cloud 20,000-50,000: Outer Oort Cloud 1955 planets beyond the solar system (exoplanet/exosolar) - Most are bigger than Jupiter, and orbit closer to their Sun than Mercury Solar System Characteristics All planets, except Mercury, orbit nearly circularly, lying on the same orbital plane. All planetary objects orbit counter- clockwise on the plane of our solar system (ecliptic) Properties (1 – 4) all refer to orbits of planets 1. Each planet is relatively isolated in space. 2. The orbits of the planets are nearly circular. 3. The orbits of all the planets all lie in nearly the same plane. 4. The direction in which all the planets orbit the Sun (counterclockwise when viewed from above Earth’s North Pole) is the same as the direction in which the Sun rotates on it’s axis. Properties (5 – 8) refer to chemical make up of SS 5. * There is a chemical and density gradient from inner (metals + rocks; high density) to outer (gas and ice; low density) outer planets 6. * Asteroids are very old; most lie between Mars and Jupiter; and most of the material expected to exist is missing. - The meteorites we find are very primitive in composition 7. The Kuiper Belt exists and is a collection of small, rocky-icy bodies beyond the orbit of Neptune 8. The Oort Cloud comets are primitive, rocky-icy bodies that do not orbit in the plane of the SS (ecliptic) and reside primarily at large distances (~20,000 -50,000 AU) Wesley Fowler ASTR Chapter 6 Planetology Terminology: - Semimajor Axis (a) distance from sun. [AU] P =a 2 3 - Orbital Period (P) (Sidereal) Time to revolve around the Sun [years] P =a 3 - Radius (R) Center-to-surface distance [km or m] F = (Gm m )/r 1 2 2 - Mass (M) Number of kilograms of matter [kg] F=ma - Rotational Period: How long each day is (hours or days) - Average Density: How much mass is in a standard volume [kg/m or 3 g/cm ]3 – Density = Mass/Volume Inner Planets: Terrestrial Worlds Outer Planets: Jovian Worlds Outer Solar System: Icy Worlds Terrestrial Planets: Within 1.5 AU of the Sun - Solid surface - Mercury, Venus, Earth and Mars - High density average Jovian (Gas Giant) Planets: Beyond 1.5 AU of the Sun - Gas surface, almost all hydrogen and helium - Jupiter, Saturn, Uranus, and Neptune - Low average density Comparative Planetology: The study of understanding planets based on how they are similar to each other. - Differences between planets are rarer than similarities, and provide very specific and substantial information for study - Mechanisms of our solar system can be applied beyond our solar system - Gives insight to formation of the solar system All four terrestrial planets have very different atmospheres - Mercury barely has an atmosphere - Venus has an atmosphere with 10x more pressure than Earth’s - Earth is the only planets with Oxygen (O ), but is primarily Nitrogen 2 (N2) - Mars has a thin atmosphere of Carbon Dioxide (CO ) 2 Rotation Speed (Sidereal Day): - Earth 23h 56min - Mars 24h 40min - Mercury 58 days - Venus 243 days (rotates clockwise, backwards to Earth and Mars) Earth has one moon, Mars has two, Venus and Mercury have none. Earth and Mercury have measurable global magnetic fields, but Venus and Mars do not. Density (kg/m ): Density decreases as the distance from the Sun increases Mercury: 5300 Venus:4400 Earth: 4400 Mars: 3800 Terrestrial planets are closer together than Jovian planets Jovian planets are massive compared to Terrestrial planets Terrestrial planets are entirely solid, while Jovian planets are gas with a solid core Magnetic field of Jovian planets are stronger than Terrestrial planets Jovian planets have many more moons than Terrestrial, they are Icy worlds All Jovian planets have ring systems Jupiter: - Most massive planet in the solar system, more than 2.5 massive than all other planet’s mass combined Outer Icy Worlds: Asteroids: - Small, rocky bodies: Smaller = lumpier - Main Asteroid Belt: Small objects mostly of rock and some metal, between Mars and Jupiter - Jupiter Trojan Asteroids: Little is known of these objects Comets: - Highly eccentric orbits - Rock, ices and organics - Originate from Kuiper Belt and Oort Cloud Wesley Fowler ASTR Chapter 6 Nebular Theory The nebular theory claims that the existing solar system was formed by the collapse of a giant cloud of interstellar gas and dust. 1. A cloud of gas and dust (nebula) exists 2. The nebula is compressed (by gravity, shockwave?) 3. Conservation of angular momentum causes nebula to rotate faster 4. The rotation speed causes the nebula to flatten into a disc called the Solar Nebula. It has a large central mass called the protosun 5. The dense materials (dust) in the Solar Nebula accrete together into planets and other solar system bodies Nebular theory is well supported by visual observation! Condensation Theory Condensation refers to the changing of phases, typically from gas to liquid. However, when dealing with the solar system, it’s from gas to solid. The planets and objects farther away from the sun are composed of more materials than the ones closer to the sun - This is called the compositional gradient of the solar system The planets and objects farther away from the sun have lower temperatures than the ones closer to the sun - This is called the temperature gradient of the solar system The temperature gradient of the early Solar Nebula explains why rocky planets formed close to the sun, while planets farther away remained gaseous. - Solid materials require higher temperatures to condense - Solid materials have higher densities than gaseous ones Hot: 1200-1500 K Warm: Around 500 K Cool: 200-300 K Cold: Around 50 K Ice Line: (T = 273 K) - Boundary in which icy grains can form Planet Building 1. Condensation of solids (Condensation Theory): Two grains of ice for each grain of rock - Inner SS: Rock and Metal grains available - Middle SS: Metal, Rock, and High T ices (e.g., water) - Outer SS: Metal, Rock , High and Low T ices 2. Accretion of solids: Grains clump together in the protostellar cloud - More material is available farther from the sun due to lower density, thus larger planets 3. Collection of solid grains into planetesimals: Grow from cm to km - Gravitational attraction begins when planetesimals reach 10-100km in size - Leftovers of these are asteroids! 4. Formation of protoplanets out of planetesimals: Begin to have strong gravitational force - 100 – 1000+ KM in size 5. Combination of protoplanets via collision - How we think the moon was formed, why Venus rotates “backwards” This process explains how terrestrial planets, rocky cores of gaseous planets, and other SS objects are formed. The sequence takes about 100 million years. Core-Accretion Theory Much larger protoplanets form beyond the ice line due to the abundance of materials that have not condensed. - Gas giant planets have solid cores that have an immense gravitational force. These cores attract huge amount of gas from the nebula itself, and thus become massive. The core-accretion theory is disapproved of by many scientists, as the time required for the exceeds beyond the lifetime of solar nebula Gravitational Instability Theory The giant gaseous planets formed in a very similar way that the Solar nebula did, with gases from the original nebula condensing into planets The gravitational instability theory is disapproved of by many scientists because there is simply not enough mass in the solar disc to cause this type of gravitational collapse. The core-accretion theory is currently better supported than the gravitation instability theory. Clearing the Disk Strong solar winds blow interstellar dust, gas, and leftover planetesimals out of the solar system. This isolates and defines the specific planets and interstellar objects Wesley Fowler ASTR Chapter 7 The Earth’s Structure Earth is the most massive of the terrestrial planets, it has very dense materials in its interior, it is the only planet with liquid water on its surface. • Inner Core: 0 - 1300 km (solid) • Outer Core: 1300 – 3500 km (liquid) • Mantle: 3500 – 6350(ish) km • Crust: 5 – 50 km thick – Oceanic Crust: ~5 km thick – Continental Crust: ~ 30 – 50 km thick • Hydrosphere: All water • Atmosphere: Crust – 100 km (Point at which flight is not possible) • Magnetosphere: >100 km The Earth’s Atmosphere The outgassing of water vapor, methane, CO , and2nitrogen compounds from the Earth’s surface is the origin of the atmosphere. These compounds are altered by the Sun’s UV light in a process called photodissociation, which breaks up nitrogen compounds, isolating nitrogen. Nitrogen clumps together to form N gas2 which is very inert and hard to break up. - Remaining compounds absorbed into rocks Oxygen enters the atmosphere from photosynthetic organisms in the ocean. Nitrogen 78% Oxygen 21% Argon 0.9% CO ~ 0.03% 2 Troposphere: Lower level of atmosphere. All weather occurs here. (0-17kn) Stratosphere: Where the ozone layer is, and where planes fly. (17-50km) Mesosphere (50-80kn) Ionosphere/Thermosphere: Ionized molecules and free electrons here. (80+km) Temperature Inversions define the boundaries between layers - Temperature increases in ozone layer with ascension due to o 3 absorbing sunlight, Troposphere: Air is constantly being moved around through convection, which is driven by Erath’s warm surface due to sunlight. - Convection is the transfer of heat from one pace o another through the movement of a gas or liquid. Astrosphere: Ozone layer is an excellent absorber of UV radiation, why there is the temperature inversion The ozone hole: Large hole in the ozone layer above Antarctica, caused by pollution of chlorofluorocarbons (CFCs) in Antarctica, which kills ozone cells. The sky is blue because blue light is scattered in the atmosphere of of air molecules. Blue light is scattered more than red light due to its shorter wavelength (400nm), and appears to come from all directions as a result. Most red light is not scattered in the atmosphere. “Rayleigh scattered” 9.8 times more efficiently scattered than red light Mie scattered 1.75 more efficiently than red light At sunrise and sunset, the sunlight has more atmosphere to travel through, and blue light scatters out of line of sight along with greens and yellows, leaving mostly red light to be seen. Surface Heating Earth’s surface absorbs about 70% of the incident solar radiation. - Were it not for the atmosphere, the surface temperature would be 250K or -23C Greenhouse gases are molecules and compounds that efficiently absorb the infrared radiation. Include CO 2 methane, and water vapor. Warms up the -23C to 14C (57.2F) Wesley Fowler ASTR Chapter 7 Climate Change Climate: Long timescale characteristic of the environment (i.e. a dessert, a rainforest) Weather: Temporary condition (it is raining) - Climate change: The change of the average condition of the Earth. Human activity is increasing the amount of CO in t2e atmosphere, thus increasing the amount of the atmosphere’s greenhouse gases which trap thermal radiation. Thus the temperature of the world is increasing with the rise of CO emission because less and less thermal radiation is escaping 2 through the atmosphere. Possible outcomes of climate change: - Increased surface and ocean temperatures - Rising sea levels - Longer and more intense periods of severe weather - Changes in atmospheric and oceanic circulation patterns - Increase of desert area in equatorial regions - Increase in ocean acidity and larger and more numerous “dead zones” The Earth’s Interior In order to determine the internal structure of the Earth, scientists use seismic waves generated during earthquakes. - P-waves (Primary Waves) Pressure waves that travel fastest, causing vibration in the direction of motion. These can travel through solid, liquid and gases. - S-waves (Secondary Waves) Shear waves that travel slower, causing vibration perpendicular to the direction of motion. These can only travel through solids, and be absorbed by liquids and gases. By observing the difference between these two wave speeds, scientist can determine the density of the rock in the Earth’s interior. - Since S waves cannot pass through liquids, we know that there is a liquid outer core surrounding the inner core with a radius of 3500 km. Surface Activity Plate Tectonics: The oceans and continents are floating on top of a highly viscous convective mantle of in a series of plates - Earth is the only planet known to have plate tectonics. Lithosphere: The Earth’s crust and upper solid mantle made up of the Earth’s plates. - 100 km thick on average Asthenosphere: Upper mantle below the Lithosphere, a highly viscous convective mantle. - Not molten, but flowing Tectonic Motion: Plates floating on top of convection cells in the mantle. - Magma seeps to surface at cracks between plate boundaries. Volcanoes are very common in these areas. - Plates grinding or colliding against each other produces earthquakes. Pangaea Pangaea refers to the Supercontinent that housed the current continents. It explains fossil evidence, and the breakup of Pangaea explains why the continents drift about 2cm ever year. Earth’s Magnetic Field Requirements for a planetary magnetic field: 1. Convection of conducting liquid in interior - Needs to be large enough 2. Sufficiently fast rotation rate - Lower than ~25 days Dynamo Theory: The combination of these two requirements creates an electrical generator which produces an electrical field. - Earth fits this theory, and has the strongest field of all the terrestrial planets Magnetosphere: The region in space influenced by Earth’s magnetic field - Charged particles of the Solar Wind are deflected by Earth’s magnetic field Van Allen Belts: Regions in the magnetosphere perfect for trapping charged particles, which send them into the upper atmosphere, creating the aurorae (northern lights) Tides Earth’s tides are caused primarily by the moon’s gravitation force, as well as by a force from the sun that is twice as weak due to distance. There are two low and two high tides per day. - Tides are a differential force, meaning that the gravitational force from the moon is stronger on the closer side of Earth, and weaker on the farther side. (a) Tidal Bulge: The near-side’s ocean is lifted towards the moon, while on the far side the land is being pulled away from the far side’s ocean. This is why we have low and high tides. (b) - High tide is the side closest and farther from the moon, low tide in on the caps of the bulge. Determined by the tidal bulge. Spring tides are the strongest tides, and occur at a new or full moon. Neap tides are the weakest tides, and occur at a 1 or 3 quarter moon. Tidal locking: The moon’s motion is causing the Earth’s rotation to gradually slow, making the days longer by +2.3 milliseconds per century - Furthermore, the moon is retreating from Earth at a rate of 4cm per year Wesley Fowler ASTR Chapter 8 The Moon Distance from Earth: 384,000 km Radius: 1,738 km (0.27 Earth radii) Mass: 7.3 x 10 22kg (~1/8 Earth Masses) Orbital Period: 27.3 days Rotational Period 27.3 days - The moon has no atmosphere and no global magnetic field The side of the moon that can be seen from Earth is called the Lunar near side, while the face that cannot be seen is the Lunar far side. We can see about 59% of the moon due to its slightly elliptical orbit, which causes a lunar libration. - Lunar libration: The oscillation of the moon, or its rocking back and forth. The moon’s rotational period is equal to its orbital period around Earth, both being 27.3 days. This is why only the lunar near side is visible from earth. The moon is in synchronous orbit. Tidal locking: When an orbiting moon is in synchronous orbit with its associated planet. - Most moons in the solar system are tidally locked. The Moon’s Surface Two dominate surface features: 1. The Lunar Maria: The younger, smoother surface that has fewer craters. Darker in color due to high amount of iron in rock. 2. The Cratered Highlands: Elevated above maria by several kilometers. Older surface with much more craters, a lighter color. The region is filled with mountains. The Lunar near side is mostly maria with highlands at the southern tip, while the far side is mostly highlands with some scattered maria. Impact craters: Ring-like impressions on the moon created from meteor impacts. Simple craters: Clear and singular bowl shape. Simple physics. Complex craters: Large craters that have a central peak. Complex physics. Ejecta: The material ejected from the moon due to a meteor strike. - Ejecta blanket: White surrounding material around crater. - Ejecta rays: White streaks from craters that stretch across the moon. The older surfaces of the moon have more craters than younger surfaces. Superposition: What is on top is younger. If there is a crater in a mare or a larger crater, the crater is obviously younger. Radioactive dating of lunar samples is a more accurate method than crater observation. • End of Late Heavy Bombardment: 3.9 billion years ago • Formation of Maria: 4.1 – 3.9 billion years ago • Cratered Highlands: 4.4 billion years ago Regolith: The fine dust that covers the moon, caused by the breakup of the moon’s surface. - Can be over 100m deep, this is why the astronauts left footprints on the moon. - The steady buildup of regolith creates an erosion rate of 5 meters per billion years. Permanently shadowed craters provide evidence of once-existing water ice at the poles of the moon. These regions, that have never seen sunlight, contain hydrogen and water ice molecules. - Less water in these regions than the driest place on Earth.
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