Introduction to the Sky and Solar System
Introduction to the Sky and Solar System ASTR 1210
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This 10 page Class Notes was uploaded by Willie Cummings on Monday September 21, 2015. The Class Notes belongs to ASTR 1210 at University of Virginia taught by Aaron Evans in Fall. Since its upload, it has received 23 views. For similar materials see /class/209710/astr-1210-university-of-virginia in Astronomy at University of Virginia.
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Date Created: 09/21/15
These are a set of questions that should help you prepare for exam 3 Use this as a guide not a substitute for studying class notes and textbook chapters As a general rule it is easy to ask questions about the unique properties individual planets have Moon What are the primary features of the Maria and Highlands and how does this relate to how each was formed 0 Lunar highlands craters are so crowded that we see craters on top of other craters I Date to as long as 44 billion years ago heavy cratering occurred early in the solar system s history 0 Lunar maria dark colored only a few craters on top of generally smooth volcanic plains I 3039 billion years ago telling us that the lava flows that made these volcanic plains had occurred by that time Contains only about 3 as many craters as the highlands so we conclude that the heavy bombardment must have ended by about 4 billion years ao and relatively few impacts have occurred since that time Why has the moon been so crucial for the reconstruction of the bombardment history of the solar system 0 Radiometric dating of moon rocks allows reconstruction of rate of impact during much of the moon s history impacts are essentially random events so the same changes in impact rate over time applies to all terrestrial worlds and thus the degree of crater crowding therefore allows us to estimate the geological age ofa planetary surface to within a few hunrred million years or so 0 Idea that planets with lots of craters look like they did 4 billion years ago while worlds like Earth with few craters obviously have had extensive geological activity that has erased nearly all of the ancient craters How do we believe the moon formed 0 Maria formed during the heavy bombardment craters covered the Moon s entire surface The largest impacts were violent enough to fracture the Moon s lithosphere beneath the huge craters they created However moon s interior had already cooled since its formation and there was no molten rock to flood these craters immediately Lava floods came hundreds of mil years later and this heat gradually built up during the Moon s early history molten rock then welled through the cracks floowding the largest impact craters with lava 0 Maria are generally circular because they are essentially flooded craters dark color comes from the dense iron rich rock basalt that rose up from the lunar mantle as molten lava Moon formed as result of a giant impact of a Marssize body with Earth which would have vaporized water and released other trapped gases Planet Interiors What is albedo and what is its importance to planetary astronomy What is Density and what is its importance to planetary astronomy Draw a picture of the interior of a terrestrial planet and label the components What are the compositional variations due to I Core highest density material consists mostly of metals like nickel and iron in the central core I Earth s metallic core consists of two distinct regions solid inner core and molten liquid outer core I Venus may have a similar core structure I Mantle rocky material of moderate density mostly minerals that contain silicon oxygen and other elements forms the thick mantle that surrounds the core Crust the lowest density rock such as granite and basalt a common form ofvolcanic rock forms the thin crust essentially representing the world s outer skin How do we know about the inner structure of planets Average density determinations discussed previously I Local gravity variations as measured with artificial satellites I Magnetic fields molten coreconvection I Lava flow internal composition I Earthquakes internal structure In terms of planets what are the 4 principle energy sources and for which planets or period of time is each important 0 heat of accretion accretion deposits energy brought in from afar by colliding planetesimals An incoming planetsimal has a lot of gravitational potential energy when it is far away As it approaches a forming planet its gravitational potential energy is converted to kinetic energy causing it to accelerate Upon impact much of the kinetic energy is converted to heat adding to the thermal energy of the planet 0 heat from differentiation differentiation also converts gravitational potential energy into thermal energy The process of separating dense and less dense materials in interior adds mass to the planet s core and reduces the mass of the outer layers which means that mass effectively moves inward and loses gravitational potential energy The friction generated as the mass separates by density converts the lost gravitational potential energy to thermal energy heating the interior 0 Heat from radioactive decay radioactive decay affects the terrestrial worlds because the rock and metal planetesimals that built them contained radioactive isotopes of elements such as uranium potassium and thorium When radioactive nuclei decay subatomic particles fly off at high speeds colliding with neigbhrogin atoms and heating them In essence this transfers some of the mass energy of the radioactive nucleus to the thermal energy of the planetary interior I While accretion and differentiation deposited heat into planetary interiors only when the planets were very young radioactive decay provides an ongoing source of heat 0 However rate of radioactive decay declines with time so it was a more significant heat source when planets were young How do the interior regions cool off Conduction heat transfer via the macroscopicjiggling of molecules important in the lithosphere I Convection hot materials expands amp rises cool material contracts amp fails I Eruption transfer of heat to the surface by depositing lava on the surface Why are plate tectonics a thick atmosphere and rotation important in shaping the surface of a planet Erosion the wearing down or building up ofa planet s geological feature by wind water ice etc gtThe thicker the atmosphere the greater the erosion gtThe faster the planet rotates under its atmosphere the greater the erosion Tectonics the disruption ofa planet s surface by internal stresses rstress of convective currents gtstress from temperature changes due to radioactive decay gtstress from compression of lithosphere as the planet cools Atmospheres What are the atmospheres of Venus Earth and Mars comprised of What are their clouds comprised of How does sunlight heat a planet without an atmosphere le what are the important factors What does the atmospheric structure of the terrestrial planets depend on Why is the sky blue What is the greenhouse effect and why is it important Draw a diagram of the generic terrestrial atmosphere ie the Earth39s and label it Make sure you know what the primary processes are occurring in each layer 0 Troposphere lowest layer of the atmosphere The temperature drops with altitude in the troposphere o Stratosphere begins where the temperature stops dropping and instead begins to rise with altitude High in the stratosphere temps fall again Thermosphere begins at a high altitude where the temp again starts to rise Exosphere uppermost region in which the atmosphere gradually fades away into space 00 Mercury Closest planet to the Sun 04 AU 0 Negligible atmosphere 0 Heavily cratered surface 0 Unusually large iron core 0 Weak magnetic field Igneous silicate metallic rock Polar cap permanent deposit of water or other frozen volatiles in the cool polar regions of the planet Tilt of rotational axis with respect to the ecliptic plane 0 thus polar regions receive little sunlight Lots of impact craters old Surface Caloris Basin largest structure on Mercury 1000 km created by an impact with an asteroid How do we believe that Mercury came to obtain its relatively large core 0 Created with a disproportionately large core via a collision with a large planetsize asteroid 0 If this happened after differentiation much of the crust material could have been lost Does Mercury have evidence of volatiles on its surface and if so where are they where did they come from and why are they still there Polar cap permanent deposit of water or other frozen volatiles in the cool polar regions of the planet Caloris basin has them came from asteroid impacts Venus Second planet from the Sun 07 AU 0 Thick atmosphere composed primarily of C02 0 High surface temperature 0 Clouds of Sulfuric Acid 0 Extreme Greenhouse Radarconstructed map of heating 800K at the surface Coronae failed or developing hot spots Why is the surface temperature of Venus so high Greenhouse effect Venus has no large craters and no erosion What is the most likely explanation for this No large craters surface doesn t date back to heavy bombardment period No small craters they burn up in the thick atmosphere no erosion because rotation period is over 200 days and very slow Mars Discussed thus far 0 Noncircular orbit 0 Atmosphere of C02 95 0 Greenhouse Effect 0 Dust Storms ron oxide sand amp dust 0 Volcanic rocks Shield Volcano Volcanoes which build up massive domes with gentle sopes from an eruption of fluid basaltic lava 0 Summit Crater Produced by the collapse of the surface when the underground pressure of the magma subsides 0 The proximity of Mars to the asteroid belt results in higher cratering rates than most terrestrial objects Why does Mars have seasons What other planets have seasons The polar axis of Mars is tilted 25 with respect to the ecliptic plane 0 End result 9 Mars has seasons 0 Effects 1 Varying size of polar caps 2 Dust Storms 3 Change in Albedo of the Surface 0 The Albedo of the surface changes with the seasons It s actually due to the uniform blanketing of dark underlying rocks by fine lighter colored sands How do Mars and Pluto lose part of their atmospheres during their winter months What limits the size of mountains on terrestrial planets le why can Mars have higher mountains than the Earth Size of Mountains are limited by the planet s surface gravity amp the crustal rock strength Mars can have high mountains because its surface gravity is low What is the evidence of pastpresent water on Mars Erosion features present gt Some features carved by water Runoff chanels present 1 running water on Mars requires thicker warmer atmosphere 2 running water contributes to erosion quotBlueberriesquot contain ironrich hematite which is formed in water indentations created in standing water ancient river beds gullies remainder probably now underground as ice and volcanoes have melted the ice but when they come up to ground they evaporate or freeze What makes the ejecta blankets surrounding Martian craters smoother than those seen on the Moon or Mercury Impact Craters smooth ejecta blankets fluidized ejecta caused by ice vaporized by impact 0 On the Moon and on Mercury the ejecta typically have a coarse disordered texture close to the rim Farther out the texture becomes finer and with increasing radial distance grades imperceptibly into dense fields of secondary craters and rays Most Martian craters have quite a different ejecta pattern The ejecta commonly appear to consist of several layers with the outer edge of each marked by a low ridge or escarpment Features on the ejecta surfaces include closely space radial striae and concentric grooves ridges and scarps especially toward the outer margin These unique Martian features were seen vaguely in the Mariner 9 pictures and tentatively attributed to wind action Jovian Planets Low Densi 0 Small quotCorequotAtmosphere Ratio 0 Rings 0 Lots of Satellites Dense core required to account for gravitational field composed of things denser than Hydrogen amp Helium How is it that the Jovian planets have large atmospheres relative to the terrestrial planets and why are their atmosphere primarily hydrogen and helium ie as opposed to the heavier atoms and molecules contained in the Earth39s atmosphere Make sure that you can identify the Jovian and terrestrial planets by appearance What causes the beltzone structure of Jupiter39s atmosphere Strong Coriolis forces divide circulation cells into bands 0 Convection results in bands of different color gt Zones rising cooling air out of which ammonia condenses into clouds gt Belts falling air depleted in clouds allows clouds below to be seen Why does Saturn appear so flattened Which Jovian planets have internal heat sources and what is the cause Source of heat from Jupiter is the slow contraction of the planet Source of heat from Saturn is Helium rain Source of internal heat for Neptune is primordial contraction of ice and rock Jovian Magnetic Fields Source of particles in Magnetic Fields 0 Jupiter solar wind amp volcanically active lo 0 Saturn solar wind 0 Uranus primarily protons amp electrons from hydrogen escaping the planet s atmosphere 0 Neptune protons amp electrons from hydrogen escaping the planet s atmosphere amp Nitrogen from Triton s atmosphere Source of Magnetic Field 0 Jupiter amp Saturn metallic hydrogen 0 Uranus amp Neptune pressureionized ice oceans of hydrogen How are planetary rings formed How does the size of the grainsrocks that make up the rings affect their visibility Composition mixture of rocks of varying sizes comprised mostly of water ice high albedo 0 Dimensions of Saturn s rings 270000 km x 105 of meters 0 Roche zone tidal forces N binding gravitational forces 0 Note smaller rocks are held together by gravitational amp electrostatic forces amp thus can survive Jupiter s rings are smaller because of smaller particles Gaps are present in the rings They are created by Gap Moons that nudge particles out of particular orbits 0 Spokes particles levitated out of ring plane by forces associated with the magnetic fields origin of rings Large moon that strayed too close 0 Tidal forces prevented a large moon from ever forming there Saturn has seasons as does Uranus Uranus blue because of methane gas Density high so not the same composition as Jupiter and Saturn large core of ice and rock Jovian Moons Make sure you know why the moons lo Europa Enceladus Titan and Triton are of such great interest Europa surface mainly water and icesimilar to earth Streaks amp ridges are cracks in icy surface 0 Ridges may result from material being squeezed up from below 0 Purity of surface 9 resurfacing process 0 No evidence of impacts 0 Source of energy for resurfacing Tidal Heating by Jupiter o Thin atmosphere of sulfur dioxide note again sulfur amp oxygen from o are major contributors to charged particles in Jupiter s atmosphere 0 No impact craters 9 surface is young White surface sulfur dioxide Other regions hydrogen sulfide dulfur sodium Io s surface young due to volcanoes Volcanic hot spotslava lakes 0 Gravitational pull of Europa amp Ganymede keep o from achieving circular orbit 0 Thus o experiences tidal torques as it approaches amp recedes from Jupiter Enceladus Surface a mixture of soft craters amp complex fracture terrains 0 terrains N few hundred million yr old Cryovolcanism flow of partially melted ice that mimics lava flows on silicate planets 0 Spray of H20 ice particles observed emanating from Enceladus 0 Looks like lo but Enceladus isn t forced into noncircular orbit by companion moons like o Has blue streaks warmer than surrounding regions heat leak Saturn s Bfield is bent around Enceladus due to the interaction between particles in the moon s atmosphere amp the Bfield Titan Surface is not visible through thick clouds thus the need for CassiniHuygens mission Atmosphere 10 times that of earth 10 times more extended nitrogen and menthane No water vapor low temps keep water frozen Atmosphere from outgassing and comets hydrogen escaped nitrogen accumulated Narrowband infrared to see through clouds 0 Light amp dark surfaces visible 0 Dark spots 9 deposition of methane Chanels caused by methane rain and subsurface springs Orange in color due to attenuation of blue light compared to red Triton Orbit moves in direction opposite Neptune s rotation 9 Le irregular satellite 9 It is likely a captured kuiper belt object Pinkish color 1 Southern hemisphere flat plains covered with dark spots 2 Latitudes above equator smoothuniform material with uniform tint 3 Higher Iatitudesrough terrain crossed by long grooves quotCantaloupe Terrainquot What is the geological evidence for the shaping of Titan39s by methane rain or subsurface springs Make sure you can answer general questions relating what is seen on the surfaces of these moons to the age of the surface Regular Satellites having orbits of low eccentricity near the equatorial plane of their planet 9 Formed in the quotsubnebulaquot surrounding planet Irregular Satellites having orbits of large eccentricity high inclination or both 9 Captured from elsewhere Extrasolar Planets Extrasolar planet is beyond our solar system orbiting star other than sun What are the four possible methods one can use to find extrasolar planets and which method has been the most successful 1 Direct imaging difficult to do due to light contrast between planets and small angular separation 2 Transits If a planet crosses transits in front of its parent star39s disk then the observed visual brightness of the star drops a small amount The size of the eclipsing object and its orbital period can be derived from these observations Problem 1 unless the planet is large in size relative its star as seen from our vantage point this effect will not be significant Problem 2 the orbital inclination relative to us must be such that we see the planet transiting the disk of the star solutions Look at lots of stars at once 0 Look for a relatively long time 0 Focus on low mass stars The smaller the star the stronger the signal from a transit event 3 Star s wobble Both the star amp planet move around a center of mass The location of the center of mass depends on the mass of the star and the planet 4 Radial velocity radialvelocity method uses the fact that a star with a planet will move in its own small orbit in response to the planet39s gravity The goal now is to measure variations in the speed with which the star moves toward or away from Earth In other words the variations are in the radial velocity of the star with respect to Earth The radial velocity can be deduced from the displacement in the parent star39s spectral lines due to the Doppler effect This has been by far the most productive technique used by planet hunters It is also known as Doppler spectroscopy The method is distance independent but requires high signaltonoise ratios to achieve high precision and so is generally only used for relatively nearby stars out to about 160 lightyears from Earth What are the biases inherent in the successful search technique and what kinds of planets have been found as a result of this bias The majority of extrasolar planets found to date are very massive amp very close to the host star Note the observational bias 9 the most successful techniques favor the identification of massive planets close to their host star How do the extrasolar planetary systems different from our solar system The size of one was measured from an eclipse event to have a diameter 135 times that ofJupiter 0 Density N 06 Jupiter density 0 If this is typical then the extrasolar planets are gas giants Chapter 14 The sun Formed by Thermonuclear Fusion combining 2 atonomic nuclei at high temperature to create new more massive atom and release energy The nuclei are positively charged which causes electromagnetic repulsion the high temperature creates more kinetic energy and the nuclei get closer and strong nuclear force pulls them together 0 Fundamental forces I Gravity works over long distances holds Earth in orbit around Sun I Strong and weak hold nuclei together and participate in radioactive decay Electromagnetic hold atoms together 0 Fusion I The way by which elements heavier than hydrogen are built I Hydrostatic equilibrium the balance between the forces of the outward radiation pressure from fusion reactions and the inward force of gravity is what keeps the stars stable 0 Outward radiation pressure inward gravity 0 Sun primarily hydrogen and helium 0 Interior of sun 0 Core center of sun 0 Radiative core region of sun where energy is transported via radiation 0 convective zone region in the sun where energy is transported to the photosphere via blobs of warm rising gas 0 photosphere region where viable light escapes o sunspots region of solar photosphere that is cooler than surrounding areas thus darker o corona outer atmosphere of sun coronal gas expands and flows away from Sun to form solar wind 0 22 year cycle in which the solar magnetic field reverses direction has two 11 year sunspot cycles Chapter 15 and 17 Stellar Evolution 0 Low mass stars 0 Fusion of hydrogen into helium o The core hydrogen end the star collapses hydrogen fusion forms in outer shell 0 Core continues to collapse outer shell expands given hydrogen fusion star brightens 0 Core is sustained by electron pressure outer shell dumps helium ash on core 0 Helium flash helium fusion begins in core 0 Core helium fusion ends leading to hydrogen and helium fusion shells and a degenerate carbon core 0 Outer layers drift away leaving naked core white dwarf 0 High mass stars Successive episodes of shell fusion occur causing degenerate iron core No energy released through fusion fission Core continues to accrete iron ash until degeneracy is broken Supernova caused by core bounce release of neutrinos that blow off the outer envelope of star 0000 Chapter 12 Asteroids and Comets o Asteroids one of the most probably parent bodies of meteorites are rocky O O O O O O O O Identifiable in short exposure images given their relative proximity to earth and their speed Dark asteroids dark because they absorb light and reflect little light carbonaceous Light asteroids light because they reflect significant amount absorb little silicatestonymetallic Heavily cratered Jupiter causes collisions due to orbit differences scatters some asteroids out of the asteroid belt Resonance orbital condition in which one object is subject to periodic gravitational perturbations by another usually when two objects orbit a third have revolutions that are simple multiplesfractions of each other Trojan asteroids objects at the Lagrange points gravitational force of Jupiter and Sun are exactly balanced with the centrifugal force required to rotate the objects Near Earth Asteroids asteroids that cross orbit of Earth can become thus by being nudged into these orbits by gravitational influence of planets will either hit earth or be gravitationally ejected o Meteorites remnants from formation of the solar system 0 O O O O O O O Meteoroid small piece of debris in space Meteor space debris heated by friction as it plunges into earth s atmosphere Meteorite space debris that has reached ground Primitive dating to creation of solar system I Stony carbon rich Differentiated originally part of larger object that processed material to a different form because of decay that releases heat I Metal rich rocky Falls and finds Easiest to find in Antarctic given the ice Originated from asteroid belt 0 Comets primitive objects containing substantial quantities of water ice and other volatiles form at low temperatures outer part of solar system 0 O O OO O O Nucleus small solid body from which atmosphere is released equal quantities of silicates and ice Coma atmosphere that surrounds nucleus Tail long streamers of gas and dust sweeping away from the sun I Plasma straight points away from Sun ionized gas blue color I Dust curved tail dust grain yellow white in color Death of comets I Solid material is carried away with evaporating ices leaves nothing I ce evaporates leaves rocky material that becomes Near Earth Asteroid I Impact with a planet or the Sun Meteor shower dust from comet that trails the comet in its orbit Long period comet I Extremely eccentric orbits high inclinations period as long as 1 mil yrs Short period comet I Small inclinations periods 20100 ys Kuiper Belt Object disk like distribution short period comets I Beyond orbit of Neptune lie in orbit of Pluto I Classical and Scattering KBOs I Origin 0 Leftover from circumstellar disk I Planetesimals whose accretion was disturbed and halted by formation of Neptune o Oort Cloud long period comets spherical distribution Chapter 7 and 8 Planetary system formation of solar system Table 72 Comparison ofTerrestrial and Jovian Planets Smaller size and mass Larger size and mass Higher density Lower density Made mostly of rock Made mostly of hydrogen helium and metal and hydrogen compounds Solid surface N0 solid surface Few if any moons and Rings and many moons no rings Closer to the Sun and Farther from the Sun and closer together with farther apart with cool warmer surfaces temperatures at cloud tops Cm39mx u saw an a auxquot if mm a my ma an aim Nebular Theory Our solar system formed from the gravitational collapse of an interstellar cloud of gas Solar system comes from gas clouds Heating as the nebula collapsed gravitational potential energy 9 kinetic energy heat The Sun formed in the center I Spinning conservation of angular momentum ensured that everything didn t collapse into the center I Flattening random motion dampened out through collisions leaving flattened rotating disk Four Types of Nebular Material I Gas what makes up planetary atmospheres I Ice Volatiles molecules that are liquid or gaseous at moderate temperatures but form solidscrystals at low temperatures eg Water H20 Carbon dioxide C02 Methane CH4
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