Chapter 29: Our Slar System Sectin 1: Overview f Our Slar System Objectives: 1. Describe early mdels f ur slar system. 2. Examine the mdern helicentric mdel f ur slar system. 3. Relate gravity t the mtins f celestial bdies. A. Overview f Our Slar System Earth is ne f eight planets revlving arund, r rbiting, the Sun. All f the planets and mst natural satellites r rbit the Sun in the same directin, and all their rbits lie near the same plane. B. Early Ideas 1. (Earth-centered) mdel Culd nt explain certain aspects f planetary mtin (like the retrgrade mtin f Mars in ur sky) 2. (Sun-centered) mdel 3. [Jhannes] Kepler s First Law Based n Tych Brahe s bservatins f planetary psitins States that each planet rbits the Sun in an, which is an val shape that is centered n tw pints called fci Majr axis: the maximum diameter f the ellipse, which runs thrugh bth fci, ne f which is always the Sun Semimajr axis: half f the majr axis; equal t the average distance between the Sun and the planet - Is the rati f the distance between the fci t the length f the majr axis 29-1
Is a value between 0 and 1, where numbers clser t 0 indicate mre rbits (lw eccentricity) and numbers clser t 1 indicate mre rbits (high eccentricity) - : the length f time it takes fr a planet r ther bdy t travel ne cmplete elliptical rbit arund the Sun - : when a planet is at its clsest pint t the Sun - : when a planet is at its farthest pint frm the Sun - Astrnmical unit (AU): ; the average distance between the Sun and Earth, which is used t measure the distances between the Sun and each planet 4. [Jhannes] Kepler s Secnd and Third Laws : because a planet mves fastest when clse t the Sun and slwest when far frm the Sun, equal areas are swept ut in equal amunts f time Kepler s Third Law:, where P is the rbital perid measured in Earth years and a is the semimajr axis f the rbital ellipse measured in AU C. Gravity and Orbits In 1684, English scientist published a mathematical and physical explanatin f the mtins f celestial bdies: : every pair f bdies in the universe attract each ther with a frce that is prprtinal t the prduct f their masses and inversely prprtinal t the square f the distance between them Where is the magnitude f the gravitatinal frce between the tw pint masses, is the gravitatinal cnstant, is the mass f the first pint mass, is the mass f the secnd pint mass, and is the distance between the tw pint masses Each planet rbits a pint between it and the Sun called the, which is the balance pint between the tw 29-2
rbiting bdies If ne f the tw bdies is mre massive than the ther, the center f mass is clser t the mre massive bdy. Sectin 2: The Terrestrial Planets Objectives: 1. Describe the prperties f the terrestrial planets. 2. Cmpare Earth with the ther terrestrial planets. Our slar system s planets can be gruped int tw main categries accrding t their basic prperties: (1) Terrestrial planets: the inner fur planets that are clse t the size f Earth and have slid, rcky surfaces; Mercury, Venus, Earth, and Mars (2) Gas giant planets: the uter planets that are large, gaseus, and lack slid surfaces; Jupiter, Saturn, Uranus, and Neptune A. Mercury Is the clsest planet t the Sun Has n mns Is smaller (~ the size f) Earth and has less mass than Earth 1. Atmsphere Essentially nnexistent what little des exist is cmpsed primarily f and 2. Surface Mapped by Mariner 10 (US prbe) in 1974-75 Is cvered with craters and smth, relatively crater-free plains Has planet-wide system f cliffs, called, which may have develped as Mercury s crust shrank and fractured early in it s gelgical histry 3. Interir Has high density = an extensive Ni-Fe cre (~42% f Mercury s vlume) B. Venus Is the 2 nd planet frm the Sun 29-3
Has mns Has a high albed (0.75 r 75%), which with its clse prximity t Earth makes it the brightest planet in Earth s night sky 1. Atmsphere Pressure Earth atmspheres Primarily and N 2 with cluds f sulfuric acid (H 2 SO 4 ) à intense greenhuse effect 2. Surface Mapped by Magellan (US prbe) in 1989-1994 using radar reflectin Has been smthed by vlcanic lava flws and has nly a few impact craters Experienced mst recent glbal episde f vlcanic activity ~ 500 millin years ag (mya) Shws little evidence f current tectnic activity Has n well-defined system f crustal plates 3. Interir Is mst likely similar t Earth because the size and density f Venus are similar t Earth Is therized t have a liquid metal cre that extends halfway t the surface Has n measurable magnetic field despite liquid cre, which is prbably due t Venus s slw rtatin rate C. Earth Is the 3 rd planet frm the Sun Distance frm the Sun + nearly circular rbit = in all 3 states (slid, liquid, gas) Liquid is required fr life Mderately dense atmsphere (78% N 2 + 21% O 2 ) + a mild greenhuse effect = suitable fr life Earth s axis is tilted and ges thrugh cycles f, which is a wbble caused by the sideways pull f the Mn s gravity (and the Sun s gravity) One cycle f precessin D. Mars Is the 4 th planet frm the Sun Is smaller (~1/2 the size f) and less dense than Earth 29-4
Has been explred by telescpes n Earth, and beginning in the 1960s, by prbes that have flwn by, rbited, r landed 1. Atmsphere Has a cmpsitin similar t that f Venus, but with much lwer density and pressure Has that may last fr weeks 2. Surface Is due t its high irn cntent (hence its nickname: ) Has heavily-cratered, highlands in the S hemisphere Is dminated by sparsely-cratered plains in the N hemisphere Cntains the Tharsis Plateau, which has fur gigantic shield vlcanes including Olympus Mns (which is the largest muntain in the slar system) and which is split by Valles Marineris, an enrmus canyn that lies n the Martian equatr Has plar ice caps f frzen CO 2, which grw and shrink with the Martian seasns lies beneath the CO 2 ice in the nrthern cap 3. Interir Has uncertain structure, but is thught t have a cre f Fe and Ni (and pssibly S), which is cvered by a mantle Has n magnetic field à slid cre Shws n evidence f current tectnic activity r crustal plates Sectin 3: The Gas-Giant Planets Objectives: 1. Describe the prperties f the gas giant planets. 2. Identify the unique nature f Plut. All f the gas giants Are very large Have fluid (either gaseus r liquid) interirs and pssibly small, slid cres Are cmpsed primarily f lightweight elements such as H, He, C, N, and O Are very cld Have many satellites 29-5
A. Jupiter Is the 5 th planet frm the Sun Has a banded appearance due t flw patterns in its atmsphere Has been explred by several US space prbes 1. Atmsphere Has a mean temp. 120 K (~ -153ºC; clud tps) Cmpsed f lightweight elements (mstly and ) = lw density (1326 kg/m 3 ) Cntains layer f, which is a frm f H that has prperties f bth a liquid and a metal and exists nly under very high pressure cnditins Has electric currents that flw within the layer f liquid metallic hydrgen and generate Jupiter s magnetic field Has rapidly-flwing cluds due t Jupiter s rapid rtatin lw, warm, dark-clred cluds that sink high, cl, light-clred cluds that rise 2. Mns and Rings Has the mst mns in the slar system: ttal, including the 4 large Galilean mns (1) : largest mn in slar system (2) (3) : due t Jupiter s gravitatinal frce, almst cmpletely mlten inside and underges cnstant vlcanic eruptins (4) : may have a subsurface cean f liquid water Has rings B. Saturn Is the 6 th planet frm the Sun Is the 2 nd largest planet in the slar system... ~9X larger than Earth Has a strng magnetic field that is aligned with its rtatinal axis, which is unusual 1. Atmsphere Has a mean temp. 88 K (~ -185ºC; 1 bar level) 29-6
Has an average density < density f Has flwing belts and znes due t Saturn s rapid rtatin 2. Mns and Rings Ttal mns = Saturn s largest mn,, is larger than Earth s mn and has an atmsphere made f and methane (CH 4 ) Ring system Is much brader and brighter than thse f the ther gas giant planets Is made up f, which are cmpsed f narrwer rings, called, and many pen gaps Has rings that are <200 m thick and are aligned with Saturn s equatrial plane Cnsists f particles that are prbably debris left ver when a mn was destryed either by a cllisin r Saturn s gravity C. Uranus Was discvered in 1781 by English astrnmer Sir William Herschel, wh first thught it was a cmet Is the 7 th planet frm the Sun Is 4X as large and 15X as massive as Earth Has a strng magnetic field 1. Atmsphere Has a mean temp. f 59 K (~ -214 C) Has a, velvety appearance (due t CH 4 gas) Has banded appearance but des nt have distinct belts r znes 2. Mns and Rings Has knwn mns and rings, which rbit in Uranus equatrial plane Largest mn: Rings are very dark almst black D. Neptune Was discvered in 1846 by French astrnmer Urbain Le Verrier after its existence was predicted based n small deviatins in the mtin f Uranus Is the 8 th planet frm the Sun 29-7
Has many similarities t Uranus: slightly smaller and denser than Uranus (but still ~4X as large as Earth); bluish clr; atmspheric cmpsitin; temperature; magnetic field; interir; and rings 1. Atmsphere Has a mean temp. f 48 K (~ -225 C) Has a cmpsitin like Uranus Has a banded appearance Has distinctive cluds and atmspheric belts and znes (similar t thse f Jupiter and Saturn) 2. Mns and Rings Ttal mns =, Neptune s largest mn, has a retrgrade rbit (rbits backward), a thin atmsphere, and nitrgen geysers. Has rings cmpsed f micrscpic dust particles E. Plut Was discvered in 1930 by American Clyde Tmbaugh at the Lwell Observatry in Flagstaff, Arizna Is very different frm the eight planets f ur slar system Cannt be classified as a terrestrial r gas giant planet reclassified as a in 2006 Lcated in the Has prperties mre similar t mns f the gas giants than t thse f any ther planet Cmpsed f ½ ice and ½ rck (indicated by density) Atmsphere cmpsed f unknwn quantities f,, and carbn mnxide (CO) Highly eccentric rbit 50 AU at aphelin and ~30 AU at perihelin Satellites: Charn* (1978), Nix (2005), Hydra (2005), and S/2011 P1 (2011) Sectin 4: Frmatin f Our Slar System Objectives: 1. Summarize the prperties f the slar system that supprt the thery f the slar system s frmatin. 2. Describe hw the planets frmed frm a disk surrunding the yung Sun. 3. Explre remnants f slar system frmatin. 29-8
A. A Cllapsing Interstellar Clud Our slar system may have begun when an (cmpsed f dust and gases, such as H and He) started t cllapse due t gravity and became cncentrated. Initially, the cllapse is slw, but it accelerates and becmes much denser at its center. Rtatin slws the cllapse, and the clud becmes a rtating disk with a dense cncentratin at the center that eventually will becme the Sun. B. Sun and Planet Frmatin As the slar nebula began t cl, different elements and cmpunds cndensed based n their distance frm the Sun. cndensed clse t the Sun, where it was warm; these cmprise the terrestrial planets. cndensed far frm the Sun, where it was cl; these cmprise the planets further frm the Sun. Once the cndensing slwed, the tiny grains f cndensed material started t accumulate and merge tgether t frm larger bdies, called. As the gas giants frmed, their gravity attracted additinal gas, dust, and planetesimals. This material ultimately frmed the satellites and rings f the gas giants. Due t their prximity t the Sun (and its gravitatinal frce), the inner planets were unable t acquire much additinal material. Initially, the inner planets had n. Eventually, mst f the leftver interplanetary debris crashed int planets r was swept ut f the slar system. C. Asterids Have sizes ranging frm a few km t abut 1000 km in diameter Have pitted, irregular surfaces May break int meterids D. Cmets Are remnants frm slar system frmatin Have highly eccentric rbits arund the Sun May becme disturbed by the gravity f anther bject and thrwn int the inner slar system frm ne f the cmet clusters 29-9
Peridic cmets (AKA shrt-perid cmets): cmets which have rbital perids f years Begin t evaprate when they near the Sun : the small slid cre that releases the gas and dust particles, which, when heated, frm the cmet s cma and tails : the glwing gas arund a cmet s nucleus : the glwing streams f gas and dust that trail behind cmet and always pint away frm the Sun E. Meterids, Meters, and Meterites : interplanetary debris, smaller than an asterid : the streak f light prduced when a meterid enters Earth s atmsphere and burns up : a meterid that enters Earth s atmsphere and cllides with the grund instead f burning up : ccur when Earth intersects an interplanetary debris field, such as that left behind a cmet, and numerus debris particles burn up as they enter Earth s upper atmsphere «Mst meters are caused by dust particles frm cmets, while mst meterites, which are slid chunks f rck that reach Earth s surface, are fragments f asterids. 29-10