Formation of Solar System & Planetary Moons: Study of Terrestrial & Giant Planets - Prof. , Study notes of Astronomy

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Lecture 10 10/2 –  Terrestrial Planets  Mercury  Cratering, no volcanism, and very similar to the moon  Venus  Large atmosphere  Mars  Temperature= 210 K  No conclusive evidence of life  Surface of mars, weathering covers over old craters  Several regions have evidence of water at one point  Water frost, snow, and ice exist on mars  Surface is alkaline with calcium carbonate (like limestone) associated with ice  Earth  71% covered by water  Mantle, outer core, inner core (mantle is fully molten)  250 million years ago, all continents were connected  Plate tectonics drive change  Oldest intact rock found is about 4 billion years old https://elms.umd.edu/courses/1/201208_ASTR100_lgm/content/_4049794_1/astr100_lect10.pdf? bsession=533746046&bsession_str=session_id=533746046,user_id_pk1=2172618,user_id_sos_id_pk2=1,one_time _token= Lecture 11 10/9-  Formation of the Moon  At 70 million years, the moon was created by the impact of a mars-sized body  Glancing impact which threw material into orbit around earth  Material collected together to form moon  By the end of the 150 million year period, the earth was nearly its present mass and surface was nearly solid  The early Earth’s atmosphere  Earth may have started with a hydrogen atmosphere which it could not hold for long  During the collision forming the moon, all of this atmosphere was lost  The lava surface continued out gassing-restoring the atmosphere  The atmospheres of the terrestrial planets come from:  Outgassing from lava flows which released gasses that were trapped in rock during the formation of the planet  Continued bombardment of the planet by comets  The amount of carbon dioxide in rocks on Earth is comparable to the amount of CO2 in the present Venus atmosphere  Earth’s atmosphere today  Mostly nitrogen, oxygen, and a little carbon dioxide  Atmosphere of Venus and Mars  Dominantly CO2  3% nitrogen  Tiny amounts of oxygen  Why are the terrestrial planets atmospheres different?  The key is gravity, if the body has enough mass the gas is trapped forever. If the body has too little mass, the gas can escape quickly.  The moon and mercury have too little mass  Mars may have had enough mass that is just now losing the last of its atmosphere  Possible history of Mars  When mars was young volcanism was strong, the atmosphere slowly leaked away into space but was replaced as long as there were volcanoes  As the core of mars cools, the volcanoes became fewer and the atmosphere was lost faster than it was replaced  Venus atmosphere  Venus is close to the sun-hotter, more volcanoes more CO2 and no way to get rid of it. It kept building up until the current atmosphere of Venus is 90 times as thick as the earth’s  Greenhouse Effect  Certain gasses, CO2 and methane, are transparent to visible light but good at absorbing infrared light. Sunlight comes in and its energy never escapes  On earth, the carbon cycle is self-regulating with carbon dioxide being created and locked-up  The global temperature responds to changes in the amount of CO2 in the atmosphere https://elms.umd.edu/webapps/portal/frameset.jsp?tab_id=_2_1&url=%2fwebapps%2fblackboard%2fexecute %2flauncher%3ftype%3dCourse%26id%3d_866906_1%26url%3d Lecture 12 10/11-  Jupiter  10 times diameter of earth  5.2 AU  Small rocky core with a lot of gas  95% of mass is hydrogen and helium  Very faint rings and total of 63 moons known to date  Four biggest discovered by Galileo and are “Galilean moons”. Ganymede is the largest moon in the solar system (larger than mercury)  Lo- rocky with sulfur volcanoes  Europa- smooth icy surface, may have liquid interior  Ganymede- icy dusty surface, may have plate motions like earth  Largest moon in solar system  Calisto- icy moon heavily cratered  Saturn  95 times the mass of earth, 1/3 size of Jupiter  Area recovery= 100’s of years  Global destruction  Meteorite is 25 km in diameter  If one hit in Kansas most higher life in North America would be dead in 10 minutes due to ejecta and flash fires  Mass Extinctions  Cretaceous-Tertiary extinction event:  65 million years ago  Dinosaur extinction event  Enabled rise of mammals  Triassic-Jurassic extinction event:  200 million years ago  Nearly ½ of living species at time went extinct  Enabled rise of dinosaurs  Ended domination by large crocodile-like  Permian-Triassic Extinction event:  251 million years ago  96% of marine species, 70% of terrestrial vertebrates went extinct  Killed off giant insects and major land species  Late Devonian Extinction event:  364 million years ago  50% to 75% of species went extinct  May have been cause by super volcanoes  Ordovician-Silurian extinction event:  440-450 million years ago  May have been cause by major land mass moving to south pole, causing major ice age and drop in ocean level  Formation of Our Solar system  Sun contains 99% of the mass in the solar system and is composed of hydrogen and helium  The orbits of the planets are nearly in a flat disk and all orbit in the same direction around the sun  The planets and objects inside 4 AU are rocky with little hydrogen gas and small amounts of hydrogen rich molecules  Planets outside 4 AU are larger than ones inside 4 AU and are rich in hydrogen  The asteroid belt and kuiper belt objects orbit in the same plane and same direction as planets  Comets are icy-cocky bodies that are generally found at the orbit of Jupiter and beyond out to 1,000’s of AU  The ages of meteorites are uniformly 4.57 billion years old  Oldest intact grains on earth are 4.4 billion years  Oldest full rocks are 4.0 billion years Lecture 14 10/18-  Solar system formation  All evidence points to there being a disk of gas and dust around our forming sun  Within the disk, icy-rocky material grew into planetessimals  In the inner solar system it was too hot for ice, so planetessimals were rocky. In the outer solar system ices dominated over rocky material  In the outer solar system the planetessimals grew faster and bigger because of the ices. And collided and coalesced to form the cores of the giant planets  Once big enough, the accreted and held on to the hydrogen gas in the outer disk  In the inner disk, the building of planets went more slowly because there was less material  By the time the terrestrial planet cores were approaching moon-size, most of the gas was gone from the inner solar system  They continued to grow by sweeping up rocky material inside of 3 AU into 4 planets  Gravitational force of Jupiter kept a planet for ever forming in the region between mars and Jupiter- and the asteroid belt is what is left of material that never formed  Jupiter’s gravity also cleared the icy rock bodies out of its orbit, and Saturn out of its. Bodies were thrown out into the Oort cloud.  A small number of these bodies were captured by the giant planets to become moons  Formation of the sun took 1-3 million years  Total formation of planets took 10-100 million years  Light-Electromagnetic Radiation  Light  In astronomy refers to any wavelength of the electromagnetic spectrum  Visible light is that range of wavelengths that human eye sees  Photon- smallest unit of light  Light of a single wavelength can be imagined as a wave  The wavelength is the distance from peak to peak  Light of different colors corresponds to photons of different wavelength  All light travels at the “speed of light”, regardless of wavelength  The wavelength is the distance between peaks, the frequency is the number of peaks that go by a point per second f=c/λ  Meters, millimeters—use for radio  Microns= 10^-6 meters—used ininfrared  Nanometers=10^-9 meters—used for visible light  Angstroms= 10^-10 meters—used for visible light  Energy of a photon E, is given by the equation:  Energy=E=h c/λ= h f  H is the symbol for Planck’s constant  Long wavelength photons have small energies shorter wavelength photons have more energy and X- ray’s and Gamma rays have the most energy  The unit for energy is the joule  White light is really a mixture of all colors (wavelengths) of visible light  Lights interaction with Matter  Matter can:  Emit light- the element of a light bulb  Absorb light- a black cloth  Reflect and scatter light- a white cloth  Emission of light  Emission arises because the matter is hot enough to emit the photons  The Planck function or curve describes how a body emits light according to temperature  All bodies emit light according to the Planck curve for their temperature  Wien’s displacement law- describes the wavelength of maximum emission of the Planck curve as a function of temperature λmax= b/T  Where λmax is the wavelength of the peak and b=2.9X10^-3 meters-K  Example: Sun has surface temperature of 5,700 K  λmax(sun)=2.9X10^-3/5700= 509nm  Stephan Boltzmann’s Law- describes how much total energy a body of given temperature emits per square meter  Emission= σT^4  Where σ is the Stephen Boltzmann constant and T is temperature  σ=5.67X10^-8 watts/m^2/K^4  Luminosity= surface area x σT^4  For spherical body-  L=4πR^2σT^4  Apparent Brightness= b= L/(4πd^2)  The farther away an object, the fainter it appears Lecture 15 10/23-  Absorption and Reflection of Light  Matter can absorb light  No type of material absorbs light of all wavelengths so the interaction is typical a combination of reflection, absorption, and transmission  Reflection   Transmission  Is the lack of absorption, occurs when the matter does not interact with light at a particular wavelength. Any material is only transparent over a range of wavelengths  Spectra in detail  Solids and gases are made-up of atoms which affect their interaction with light  Three types  Continuous spectra  Absorption line spectra  Emission line spectra  Sun’s spectrum- each horizontal stripe is a range of wavelengths. Each vertical bar is an absorption line  Origins of Line spectra  Spectral lines arise because the energy levels of atoms are quantized- that means that the atom can only have discrete energy levels like the steps of stairs  The detailed of the energy levels available to an atom depends on the element and the number of electrons  Each element of the periodic table has a unique set of energy levels- a unique signature in lines Lecture 16