sign in sign up
<<
Home , Accretion disk, L1157, Molecular cloud, Photoevaporation, Protoplanetary disk, Protoplanetary nebula

c Swinburne University of Technology, 2011 51 OF 1 AGE P HET620-M09A01:Evolution Formation: Disk Formation and Planet Formation: Disk Formation and Evolution c Swinburne University of Technology, 2011 51 OF 2 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and some of the constraints from the Solar Systemthe that standard planet formationformation models paradigm must and explain; details ofdisk cloud formation, collapse; evolution, and dispersal; chemistry and dust grain condensation; and grain growth via collisions. • • • • • In this Activity we will lookformed. at the In formation particular and we evolution will of discuss: protoplanetary disks in which are Summary c Swinburne University of Technology, 2011 51 OF 3 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and The formation of the planets. and It the has Solar been System aown is question origin. asked one We throughout of cannot the the hope ages to fundamentalEarth since fully questions itself it understand formed. in is how modern really a evolved on question aboutThroughout if our this we do course not we know haveformation how found process, the as many well clues as to ato help address. number of us As well constraints build as that a planets anyother in general planet ourstars picture formation ownin Solar model of the System, must the neighbourhood we bea now planet of able know general our ofSun. hundreds planet of formation Assuming planets ourorbiting planets paradigm Solar as should System well. be in able not to cosmically special, understandIn the this formation Activity of we the willbriefly extrasolar start review the by standard looking star atof formation some the paradigm, of star since the formationplanetary constraintswith process.disks from can are our result Once a in Solar formed, the natural System, protoplanetery formationa by-product and of disks few planets, then tens go satellites, of through and millions aincomets of complex thesebefore years. it disks. evolution dissipates We In within will theformation. look next at Activity we disk will evolution, look as more well closely as at how models grains of form terrestrial and and grow Introduction c Swinburne University of Technology, 2011 51 OF 4 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Constraints from the If we take stock ofwe what is find in a the Solarhot wide System, , range rocky planet of in thegas objects: inner and Solar System, ice the giants central a in mix the of outera Solar rocky mix System, and of icycomets. rock satellites, and Any as icy model well ofto as planets, explain formation and needs allfor icy of our the Solarevolutionary scenario objects, System that and explains needsstate the (location, a current to composition, age, model include etc.)these objects. of an all of The geometry of thescenarios. Solar System The provides planets importantspace; clues, (major they all as andorbit well minor)the asthey Sun reside constraints, in in the the on Sun; same the formation and direction; samedynamicalorbital most structuresperiods planets plane in increase spin the and with inasteroiddistance are the belt onfrom sameand relatively more the direction the eccentric Sun. regularly Kuiper inand belt We which inclined and alsoorbits these seethan smaller a the bodies range planets. are of in general c Swinburne University of Technology, 2011 51 OF 5 AGE P Credit: NASA HET620-M09A01:Evolution Planet Formation: Disk Formation and In terms of the compositionEarth, andMars) bulk in chemistry, we the find innerUranus, the ) part reside smaller farther of rocky out. the planets The Solar (MercuryThere, density System, , of is the while an planets the inner decreases with larger ringand heliocentric gas/ice an of distance. outer giants small belt (, rocky of , bodies, icyThere i.e. bodies, are i.e. clearly the more theasteroid refractory .belt materials close (which InSmall to the has bodies the centre a are Sun of chemical generally and the gradient) irregularly more Solarand volatiles shaped System farther differentiated. is and away. the undifferentiated, This hot while Sun. tells largebodies. bodies us are something The spherical about surfaces the ofclues history planetary about of their bodies, internal thermal which heating history.early can of Solar larger be System. counts planetary crater alsoand/or provide lava information covered, about also impact provide rates in the c Swinburne University of Technology, 2011 51 OF 6 AGE P Sasha c

First condensates: calcium aluminium inclusions. Credit: Krot 4.4 Gyrs have been found). ∼ HET620-M09A01:Evolution Planet Formation: Disk Formation and The refractory inclusions inSolar the Systemmeteorite formeddata about tell 4.568 us Gyrsformed that ago. a the few The first millionGyrs, solids years and and in later. the differentiated the oldest Lunar Earthwith rocks rocks ages are are between about 3–4.4 4 Gyrs oldWe know (though that terrestrial planets grains are formedformation around process. as So a before natural we by-productneed of move to the on start star to with the the general details theory of of planet , formation. we c Swinburne University of Technology, 2011 51 OF 7 AGE P In spiral , starsarms form which contain in dense the regions of gas and dust. Credit: NASAHeritage Team (STScI/AURA) and The Hubble 3 and

M 6 –10 5 particles per cm 3 in dense cores. 3 particles per cm 5 and a few pc in size. The small cores are

HET620-M09A01:Evolution Planet Formation: Disk Formation and in molecular clouds to 10 The standard star formation paradigm Stars form in molecular clouds the that. are found Molecular indust, clouds the and are stars spiral form cold, arms within of dense them when cloudsThe theyMilky of contract Way duecontains gas to a. large and numberfrom of molecular giant clouds, ranging systems withsizes in in the the order range ofas of 50–100 low 10 pc, as down a tousually embedded small few in cores M larger complexes. with Most masses temperatures molecular between clouds 10–50 have K and asa their name wealth suggests of contain . Densities range from 10 c Swinburne University of Technology, 2011 51 OF 8 AGE P to first carry away the magnetic fields which help hold the cloud up; : the final stage is the clearing of the disk, via and stellar : the rapid inside-out of cores : giant molecular clouds must contract to form molecular cores. This contraction : a strong stellar breaks out at the rotational poles, reversing the infall and : the newly formed star/disk system becomes optically visible and the is ambipolar diffusion HET620-M09A01:Evolution Planet Formation: Disk Formation and collapse phase requires identified as a ; disk dispersal phase . protostellar phase conserves angular, momentum producingthick infalling a envelope; protostar surrounded by aoutflow phase disk and anproducing optically bipolar outflows. This phase seemsphase; to be intimately connected with the disk formation T Tauri phase 1. 5. 2. 3. 4. The generally accepted paradigm of low star formation (Shu et al. 1987) is as follows: c Swinburne University of Technology, 2011 51 OF 9 AGE P To view a full-sized version of this diagram click. here HET620-M09A01:Evolution Planet Formation: Disk Formation and c Swinburne University of Technology, 2011 51 OF 10 AGE P . If the and . We will briefly look at each of gravity , thermal gas magnetic fields HET620-M09A01:Evolution Planet Formation: Disk Formation and Giant molecular clouds are held up by Cloud collapse clouds become massive enough, they can collapse due to The role of ingravitational star collapse formation and is it can rather also complex: counter& it the Ostriker effects creates of 2007). overdensities gravity which in these can overdense initiate regions (McKee these support mechanisms. c Swinburne University of Technology, 2011 51 OF 11 AGE P . Therefore and thermal 1 equation of state than this which suggests that rotation will not provide much support against slower thermal pressure The gravitational force that is trying to make the cloud collapse also has to . Pressure is related to temperature via the gas 2 . The cloud’s rotation produces an outward centrifugal force perpendicular to the rotation HET620-M09A01:Evolution Planet Formation: Disk Formation and While rotation may not be important in holding clouds up against local collapse, we will see that Supersonic means faster than the speed of sound. The speed of sound in an ideal gas depends (i) Pressure support: inside cold moleculargravitational collapse. clouds Some the clouds, however, have observed supersonic motions gas pressure which may contribute to their stability. (ii) Rotational support: overcome rotation axis that keeps thethey rotate cloud quite from slowly, with collapsing. rotationalis velocities Observations similar equivalent to to of the thermal molecular 0.3 support, clouds km/s but indicate at many clouds a that rotate distance of 0.1 pc. This rotation has an important role to play in the star and planet formation process. on the density and pressure. 2 1 provides little support c Swinburne University of Technology, 2011 51 OF 12 AGE P . The magnetic magnetic pressure 2 π G. This is generally thought to be enough to 8 B µ = mag P only affect charged particles in molecular clouds, making Magnetic fields HET620-M09A01:Evolution Planet Formation: Disk Formation and (iii) Magnetic support: them follow field linesexert rather a than magnetic obey force on gravity the (or charged dragging particles, the which acts field like along a with them). The fields It is difficult toCrutcher measure (1999) the found magnetic field fieldsupport strengths strength molecular B in clouds = molecular 20–200 againstthermal clouds. support. gravitational In collapse a and study is of about 27 ten clouds times greater than the pressure is given by: c Swinburne University of Technology, 2011 51 OF 13 AGE P (Mestel & Spitzer 1956, Mouschovias 1976). In this process ambipolar diffusion HET620-M09A01:Evolution Planet Formation: Disk Formation and In order for molecular cloudsthemselves of to this collapse magnetic support. and The commenceclouds process the which is removes star called magnetic formation pressure from process, molecular they must rid -neutral flows have been observed intheoretical molecular idea clouds of (Greaves ambipolar & diffusion. Holland, Once 1999)can the supporting finally magnetic the collapse support due has been to fully gravity. removed, the cloud there is a verymagnetic slow field slippage with them between (whereas the slowly the diffuseions neutrals away areand the unaffected magnetic neutrals by field. the in Ambipolar magnetic the diffusion field). is cloud, Thus also and the known as the “ion-neutral ions drift”. carry the c Swinburne University of Technology, 2011 51 OF 14 AGE P , increases. Observations of cloud % 3 ρ T q ∝ states that the gravitational is twice Jeans M , where the kinetic energy mainly comes from thermal energy , decreases as the density, kin - of the cloud that will lead to gravitational collapse (if supported by Jeans = 2E | the core can collapse. We can solve the Virial equation to find the minimum grav E kin | Jeans mass 2E > | grav E | HET620-M09A01:Evolution Planet Formation: Disk Formation and thermal pressure alone): mass - called the (unless the cloud is very turbulent or rapidlyWhen rotating). the kinetic, energy cores indicate that they aredensities dense high enough enough to that collapseobjects. to cores a can stellar collapse mass object, directly but to we produce do Jupiter not see mass (i.e. planetary) Core collapse For a cloud in equilibrium, the Note that the Jeans mass, M c Swinburne University of Technology, 2011 51 OF 15 AGE P objects are formed, and this process is smaller . fragmentation HET620-M09A01:Evolution Planet Formation: Disk Formation and Fragmentation Let’s assume that the JeansAs criterion the is cloud satisfied and contracts, the differentand cloud regions start is within to unstable the collapse to cloud gravitational themselves.known will collapse. as satisfy Therefore many the Jeans criterion individually c Swinburne University of Technology, 2011 51 OF 16 AGE P Spitzer images of the starfrom forming Evans regions et al. and (2009) Credit: Tyler Bourke, CfA HET620-M09A01:Evolution Planet Formation: Disk Formation and Note that the density of the cloudyet increases the by temperature many remains orders of nearly constant.decrease during as The the the free Jeans collapse fall criterion continues. process, tells Thuscriterion us small that regions locally, the of resulting the Jeans collapsing in massforming cloud must many regions, will which satisfy small show the Jeans stellar that stars cores. generally form in This clusters is covering a supported range of by sizes. observations of star c Swinburne University of Technology, 2011 51 OF 17 AGE P shining through the Eagle . in the Credit: M. McCaughrean “&Astrophysical M.Potsdam, ESO. Institute Andersen, , 2 phase, isothermal adiabatic collapse . protostar during which the temperature remains about constant. HET620-M09A01:Evolution Planet Formation: Disk Formation and Protostar phase collapse The increase in densitydepth during to the increase collapse,trapping however, and the causes thermal eventually the energy. makeswhen optical This energy the is is called cloud the notcore opaque radiated collapses. to away The and infrared, up trapped the the thermal temperature internal energy pressure increases until heatsbalances ashydrostatic the pressure). equilibrium the core,is As reached which the (i.e., temperaturedissociates builds gravity into rises, separate the molecularatoms.,H hydrogen Theprotostellar end core product surrounded is by a an quasi-static in-fallingis envelope. officially At called this a stage the core As the molecularthe cloud gravitational core potential collapses, energythe is energy dust converted must in into be, thermalwavelengths the and conserved energy. the core thermal and energy is While gainedaway optically by and the the thin, core collapse stays will cool. the be This radiated core phase of is contraction is called transparent to infrared c Swinburne University of Technology, 2011 51 OF 18 AGE P ν γ + 2 + + e He 3 + 2 K, nuclear reactions begin in the core and convert → 6 He p 4 + → H 2 H 1 4 H) into (He) via the reaction: 2 HET620-M09A01:Evolution Planet Formation: Disk Formation and K. Finally hydrogen fusion is ignited in the , and a star is born! 7 Once the central temperature reaches about 10 This nuclear energyexhausted. heats the Then core the10 and protostar shrinks halts again any and further heats core up collapse until the until temperature the reaches about is deuterium (D or c Swinburne University of Technology, 2011 51 OF 19 AGE P young pre-main , protostar (HAEBE). (TTS). . In 1972, Steve Strom coined the term T Tauri stars Herbig Ae/ (or PMS stars) are stars that are in the process of contracting onto , and ) YSOs are called ) YSOs are called

2 M < is an embedded source that has not yet broken free from its parent cloud core T Tauri star (or YSO for short) in recognition of the circumstellar material that strongly affects , protostar HET620-M09A01:Evolution Planet Formation: Disk Formation and High mass (2–10 M the and are not yet burningA hydrogen in their cores. Pre-main sequence stars (while PMS stars arecloud revealed core). sources, Like meaning PMS that stars, protostars they are have not brokenLow yet mass free undergoing (M hydrogen from fusion. their parent • • • • An aside: some definitions There are a wide varietysequence of star terms used when referringstellar to object young stars, including and alters the appearance ofprotostars, young and stars. pre-main sequence The stars. YSO So can what refer are to allT these Tauri objects? stars, Herbig Ae/Be stars, c Swinburne University of Technology, 2011 51 OF 20 AGE P . It is in large rotating disk in size to form a star. Due to 6 HET620-M09A01:Evolution Planet Formation: Disk Formation and Disk formation and evolution these disks that planets form. In this section westages will in discuss the theformation, three viscous evolution, life main and dispersal. of a : During the gravitational collapse ofcloud a molecular core, the gasof must about contract 10 by a factor conservation of angular ,momentum cloud the rotation initial is enormouslyresults magnified, in which thesurrounding by small a central protostar being c Swinburne University of Technology, 2011 51 OF 21 AGE P . . 3 .

protoplanetary disk is a theoretical disk that contains the minimal amount of refers to the proto-Sun along with the surrounding disk, though it is often used minimum mass solar nebula solar nebula HET620-M09A01:Evolution Planet Formation: Disk Formation and (erroneously) in a way that means just theThe disk disk component. itself is usually referred to asThe a mass (with the appropriate composition) to form the planets The The term “minimum mass solar nebula” was coined by Weidenschilling (1977) and technically • • • An aside: some more definitions! You will see various expressionsformed. used when reading about the disk out of which our Solar System 3 defines a mass distribution.the This minimum mass mass, distribution which can is be generally integrated between 0.01–0.02 within M a specific radius to get c Swinburne University of Technology, 2011 51 OF 22 AGE P v −→ × r −→ must increase and so the cloud spins faster. This m v - just like you feel in a car when you go too fast around = L −→ gets smaller thus r centrifugal forces HET620-M09A01:Evolution Planet Formation: Disk Formation and So as the cloud contracts, rapid rotation creates large a corner, and large sidewaysgreatest at forces the push equator youand away the from rotating the contracting cloud corner. starts to These spread centrifugal out forces and are form a disk: Protoplanetary disks form asconservation. a Angular natural momentum consequence is of given by cloud collapse due to Disk formation c Swinburne University of Technology, 2011 51 OF 23 AGE P Shocked gasmidplane in due to infall. the disk HET620-M09A01:Evolution Planet Formation: Disk Formation and The infalling gas rapidlymid-plane, reaches supersonic and velocities passes ascollapsing it through cloud. falls a to shockperpendicular the The to front shock the at dissipates disk.material the the will accrete kinetic equator onto If the energy of the mid-plane and of shocked the Evidence settle motion of gas into a cools shockthin in disk. quickly, protostellarLynds disks then 1157 was (Velusamy found the et in al. the 2002) system c Swinburne University of Technology, 2011 51 OF 24 AGE P Results of a rotational cloud collapse simulational. by (1995). Yorke et Equal density contour linesCredit: are shown H.W. Yorke, in P. Bodenheimer, red. G. Laughlin (1995) HET620-M09A01:Evolution Planet Formation: Disk Formation and The disk will reach atowards quasi-equilibrium the when centre all must the balancethe forces the disk balance: centre outward must the centrifugal be inward force, balanced gravitational and by forces the the pressure gravitational gradient force in towards the disk. c Swinburne University of Technology, 2011 51 OF 25 AGE P brighter than can be accounted for by this reprocessing, and much Excess infrared emission is seen in TCredit: Tauri stars NASA/JPL-Caltech/T. Pyle due (SSC) to their disks. HET620-M09A01:Evolution Planet Formation: Disk Formation and Observations of youngsub-millimeter stellar and infrared objects wavelengths.star,and we find If that T there we is Tauriwhich plot excess absorbs infrared stellar stars the emission. radiation This spectral and in is re-radiates energy due“irradiated”, in to the or particular distribution the infrared. “passive” dust of disks. These are in disks a the are protoplanetary called generally T “reprocessing”, disk, Tauri done at Some disks, however, are Disk evolution therefore they must have“accretion” some disks since energy the source source of of energy comes their from own. the accretion of material These within disks the disk. are called “active” or c Swinburne University of Technology, 2011 51 OF 26 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and During the accretion phaseis angular momentum transferred outwardsinwards and and accretes ontoefficiency material the of moves protostar. thedetermines angular The the momentum structure transport disk. and Lynden-Bell evolution & ofmass Pringle the and (1974) angular considered solve momentum conservation for to theand density time. as They showedspread a that radially, redistributing a function the viscous density of diskmaterial so will moves radius that inwards and angular momentum is transferred outwards. Various mechanisms havethe been transport proposed of for angularin momentum accretion and disks, mass gravitational torques, including and magnetic viscous torques. torques, c Swinburne University of Technology, 2011 51 OF 27 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Viscous torques Gas in the disk follows approximately fasterKeplerian , than so material material in further theblobs out. inner and part slow Collisions of down the between the disk neighbouring inner moves will blobs. blobs fall The inwards. of inner gas blob will speed now up be the moving too outer slow for its orbit, and so The reverse is true for the outer blob, which will move outwards. c Swinburne University of Technology, 2011 51 OF 28 AGE P is more likely to result in (Gammie 1996) since accretion is inactive. , but this has been found to be too small to Turbulent dead zones molecular viscosity Dead zone within an ,penetrate and with viscosity ionising is verycannot low. HET620-M09A01:Evolution Planet Formation: Disk Formation and result in any significant evolution over the disk lifetime. Thermal motions of the gas produce viscous disk evolution. Temperature gradients withineddies the can disk induce radial can mixing cause of convection, diskThe and material direction convective while of transferring the angular angular momentum in momentum the transfer process. dueMagnetohydrodynamic to (MDH) convection is turbulence, debated. onHawley the 1991). other Shear hand, flows isproducing in sustained much turbulence weakly more which magnetised drives promising disks angularphoton (Balbus momentum canor outwards. & lead cosmic Even to a ray smallionisation veryhowever, amount thein strong of disk the local is disk instabilities, well willThese shielded regions result from of ionising in very low radiation weak viscosity and ionisation. are MHD called turbulence Near becomes the ineffective. disk mid-plane, c Swinburne University of Technology, 2011 51 OF 29 AGE P . ∗ M = 0.5 disk M Simulation of massive disk with Credit: Sarah Maddison (Swinburne University) HET620-M09A01:Evolution Planet Formation: Disk Formation and Gravitational torques Soon after itsmassive as formation, it thethe continues infalling disk to molecular isare cloud accrete likely prone core. material quite instabilities. to from Massive This both disks candensity lead local waves to which are and the very efficient formation atangular global of redistributing momentum spiral gravitational (and material)until quasi-equilibrium through is reached. the disk c Swinburne University of Technology, 2011 51 OF 30 AGE P , and angular momentum will be will therefore lose angular momentum, and ∗ P magnetic breaking torques will gain angular momentum. ∗ P - which means it tries to make the disk spin at the same rate as the protostar’s rotation . Disk material orbiting more rapidly than ∗ P HET620-M09A01:Evolution Planet Formation: Disk Formation and material orbiting slower than The hot inner disk will berotating protostar ionised, will and be so slowed the down magnetic by field couples the star to the disk. The rapidly period, Magnetic torques If the magnetic field linescorotation from the protostar thread the disk, then the field tries to drive the disk to transferred outwards from the star to the disk. c Swinburne University of Technology, 2011 51 OF 31 AGE P Disk fraction as astar function forming regions. of The mean disk fractionobservations. cluster comes age from IR of excess various Credit: Swinburne, from Haisch et al. (2001) years 7 –10 6 HET620-M09A01:Evolution Planet Formation: Disk Formation and Disk dispersal The finaldispersal. stage ofprotostellar disks The are disk about a oldest few 10 evolution observed is (gas-rich) disk old (Haisch et al.cleared within 2001), this time so frame. the diskObviously, must be thestrongly timescale constrains ofprocess, because once disk the the diskthere has clearing dispersed, is planet noplanets. more formation material available to make c Swinburne University of Technology, 2011 51 OF 32 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Mechanisms for removingdiscussing) disk as material wellphotoevaporation as include of forming accretion the planets. surface onto of(or nearby the the Disk massive disk stars). protostar clearing by It the is is (as quite highHollenbach probable also energy we’ve & that Adams assisted radiation all (2004) been of from suggest by these that the processes photoevaporationfor the may young play the be a stellar protostar the outer role. dominant wind regions means of ofmassive and dispersal star, disks. heat UV the surface photons,along of either the with from disk, the it. evaporating the centralviscous gas star Gorti disk which or and et drags show from the the al. a importance smallobserved of nearby dust disk theluminous (2009) particles highest dispersal energy timescales. model photons (far-UV the and effects X-ray) forOnce of matching the disk different has dispersed, forms we’re of leftby with a energetic a planetary new radiation system. young hydrogen in burning star, a possibly surrounded c Swinburne University of Technology, 2011 51 OF 33 AGE P (easily (stable at volatile materials , which is depends on the local refractory materials condensation sequence HET620-M09A01:Evolution Planet Formation: Disk Formation and pressure and temperature of the nebula. The chemistry of the disk- determines that the go composition into of making the theelements raw planets. materials and As - the compounds both solar the started nebula solidsexists radiated to energy and as and condense gas a gradually solid and cooled, or different form a solid gas dust depends on grains. the Whether a substance Disk chemistry and grain condensation The interior of the nebula was hotter than the outer regions, so relatively high temperatures) dominate in the hot inner Solar System. More evaporated) condense out and dominate in the cooler outer Solar System. c Swinburne University of Technology, 2011 51 OF 34 AGE P 1400 ), and ∼ 8 O 3 ) condense at 3 ) form once temperatures 8 O 2 Si 2 700K. The ices do not condense until ∼ 1450 K. Then the silicates, like forsterite bar, from Pignatale et al. (2011). 1700 K. Metals like iron, nickel and silicon 4 ∼ ∼ ) and enstatite (MgSiO 4 SiO HET620-M09A01:Evolution Planet Formation: Disk Formation and 2 Condensation sequence Starting with thecan elemental assume chemical composition equilibriumand of to molecules the determine condense Sun, whatrefectory from solids one solids the are hotcondense nebula. oxides at of The aluminumcondense most and at titanium and drop below 1000 K. Theat sulphides, including temperatures FeS, condense temperatures are below 270 K. Right: Solarpressure nebular of 10 condensation sequence at a fixed (Mg K. The firstplagioclase anorthite feldspars, (CaAl including albite (NaAlSi c Swinburne University of Technology, 2011 51 OF 35 AGE P 273 < MaterialCorundumGehlenite Temp. (K) 1740 Fe and SiSilicates 1555 Anorthite 1455 Trolite (FeS) 1400 Carbonates 980 700 Ices 475–375 HET620-M09A01:Evolution Planet Formation: Disk Formation and Once solids beganmeteorites to tells us condense, that the thisByr metals began ago. effectively to The set condense rocks as theirdisk soon (mostly began as silicates) “internal to the condensed cool. disk clocks”. out formed, a about little 4.55–4.56 Isotopic later, about dating 4.4–4.5 Byr of ago, once the This table shows the approximate condensation sequence for the solar nebula: c Swinburne University of Technology, 2011 51 OF 36 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Interior totemperature the was orbit greaterexterior to than of the orbit 400 of , Marsthan the K, 270 nebula was K. the while less Thusterrestrial we and nebula can giants planets understand have very whycompositions. different the c Swinburne University of Technology, 2011 51 OF 37 AGE P Jet flow model which forms and dispersesthe chondrules inner through Solar System. From Liffman (2010). Credit: Kurt Liffman, CSIRO in primitive 4 C and then cooled and ◦ HET620-M09A01:Evolution Planet Formation: Disk Formation and It should be noted that the CAIs themselves are not direct condensations, but they contain minerals The existence ofspheroid chondrules inclusions (smalland igneous about their 1 refractory mm inclusions in size) solidified very quickly - withinan a hour few at minutes to theof most. a There remnantsolidification is magnetic (Acton also field evidence ethighly at energetic al. and the transient eventoccurred time must 2007). in have of the innerthe Thus existence Solar of System chondrules. a to explain There are various theorieschondrules, for the including formation the of X-wind& model Brown of (1995). Shuchondrule In etand high both al. refractory models materials through an (1994)4 the outflowing inner and Solar wind the System. launched jet close flowand to metals model the that of proto-Sun are Liffman 1970, high disperses Berg temperature et condensates al. from 2009). The a CAIs gas themselves of clearly show solar evidence composition of remelting (Marvin and et reprocessing. al. implies that there wereprocesses more violent occurring injust the gentle solar low nebulamust speed than collisions. have formedbetween Chondrules 1500–1900 in extreme temperatures c Swinburne University of Technology, 2011 51 OF 38 AGE P Stardust mission to Wild 2. Credit: Courtesy of NASA/JPL-Caltech 5 m in size. µ HET620-M09A01:Evolution Planet Formation: Disk Formation and Amorphous grains have no inherent structure in the ordering Some primordial solar nebula materialas still well. survives As in comets makethey’re their heated way to by theevaporates, inner the Solar which System, Sun can andresearch be aircrafts. some collected of These inclusters their cometary the of grains icy stratosphere minerals, are material material. by organics made The of component and grains tiny nondescript are about amorphous 0.1 One of the most surprisingto discoveries comet of Wild the 2 Stardustwas mission thesimilar discovery of to refractory CAI-type those grains found2006). in We primitive know meteorites that the (Zolenskythe CAIs et must Sun, have al. while formed comets very closepoints are to to found a very global mixing far of from5 material the in Sun. the early This solar nebula. of their . Crystalline grains, onatoms the arranged other in hand, a have regularly their repeating pattern. c Swinburne University of Technology, 2011 51 OF 39 AGE P 10 micron interplanetary dust grain Credit: Courtesy NASA/JPL-Caltech HET620-M09A01:Evolution Planet Formation: Disk Formation and To form the Earth, the tinyby grains at least that 13 condense orders out of of magnitude!the the How tiny does cooling grains this solar stick happen? nebula electrostatically; Grain needgrow growth then to is via small grow a accretion. multi-step grains in process: size grow first via collisions; and finally planetesimals Grain growth The tiny sub-micronder sized Waals grains forces, are whichuneven are held electric weak together charge short-range distributions. by forcesfractal van due aggregates, This to generally which leadsmore must spheroidal to grains. eventually Grains bound compact byare van to der not Waals form very forces strongenough to and fragment collisions them as in they turbulent grow. zones can be c Swinburne University of Technology, 2011 51 OF 40 AGE P Dust (yellow)and settling radial migration in a gas (red) disk. Credit: S.(Swinburne) Maddison Humble & (CITA) R. m µ years. 4 10 ≤ yrs to settle to the mid-plane, which is very slow. In fact it is too 7 due to the slight velocity difference between the dust and the gas. HET620-M09A01:Evolution Planet Formation: Disk Formation and The motions of small grains indrag the force nebula are strongly coupledBecause to the the grains gas do via not a feelthe gas pressure, gas they and are so moving a thethe little grains gas faster effectively that disk. feel a This “head removesresult wind” some the as of dust they their settles move orbital through angular toSun. momentum the and disk as mid-plane a and slowlyIn spirals the in simulation towards shown the in thesection image of on a protoplanetary the disk, right, red which representsdust. shows the the gas As (R,Z) while time yellow cross progresses, represents themigrate dust inwards. can The be time seen scale to of vertically the settleThe dust and rate evolution radially of depends dust on settling their is size. grain proportional about to 10 the grain radius. It would take a 1 slow to form planets before thework. disk disperses. During So the other dust processesthe settling must settling be phase, time at collisional by a growth(so few of orders grains larger of will grains magnitude shorten and settlebulk result faster of in than solids differential at smaller settling 1 grains). AU will grow Models into suggest macroscopic that grains within the c Swinburne University of Technology, 2011 51 OF 41 AGE P ¨ uttler et al. (2010) Range of potential grain-grain collision outcomes. Credit: Swinburne, adapted from G ¨ uttler et al. HET620-M09A01:Evolution Planet Formation: Disk Formation and So how do thedensity settling of grains grains grow rises,possible in outcomes which size? of a increases grain-grain As the collision:of the the likelihood sticking grains depends dust can of on stick, settles grain-grain rebound the(Blum or towards relative collisions. 2006). shatter. velocity the The High of disk probability speed There the collisions mid-plane grains areare are and the more more three their likely likely chemical to to result and result in physical in sticking. properties shattering, Icy while and low tarry speed grain collisions surfaces are likely to enhance sticking. Detailed laboratory experimentsrange show a of wide collisions possible (Blum outcomes & Wurm of 2008, G grain-grain 2010). Sticking can be viathrough hit and surface stick, sticking effects,penetration. and Rebound sticking or bouncing through bouncing can include with compactionmass and transfer. bouncing Fragmentation with andalso erosion occur. can Growth via collision havethe some problems. grain size As collision increases velocity, which so isthe does growth more the process likely or mean So to result other stall in mechanisms fragmentation. enhance need the to grain growth be process. invoked to c Swinburne University of Technology, 2011 51 OF 42 AGE P km/yr. A metre-sized grain at 1 AU will : while it may seem strange to talk about ‘metre-sized grains’, when discussing 6 HET620-M09A01:Evolution Planet Formation: Disk Formation and Another problem for planetesimalas formation a is the what ”metre-sized is barrier”.settled known to Once the the mid-plane, growing theySun. grains will If have migrate the radially radial towards driftto the rate form. is Very too small high, grainshence planets are won’t strongly drift have coupled less time to the (becausegas gas in the and the drift accretion timescalekm-sized disk for is planetesimals the generally are very viscous and mostly slow), hence decoupled while stay larger from onexperience the their the highest Keplerian gas rate orbits. of inwardspeeds drift Metre-sized due of to grains gas up drag, to with 10 spiral into the Sun1977b). in just 100 years (WeidenschillingRadial 1977a, migration of theof grains the through nebula. the disk Smallertransition mid-plane sub-cm from begins sized cm grains to to are clear km swept sized out up bodies the canNote by planetary occur on larger rapidly. terminology region grains as theyplanet spiral growth in all bodies and less the than about a kilometre in size are called “grains”. c Swinburne University of Technology, 2011 51 OF 43 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and A range ofboth the ideas metre-sizedfragmentation proposed problems use barrier to that fact that andpile get grains the up around at grain stall a radial migration pressuregrain fragmentation, and maxima. since lower thebetween grains relative the is velocity substantially This lowered rate inpressure can these maxima of and grain canThis therefore means grow. that if grains can becomea trapped pressure in maxima they can grow atand a rapid then rate decouple fromtheir radial the migration. gas, which stops Several regions havedust been in proposed pressure maxima, to includinget al. at trap the 2007) edge and at ofet the the al. ice-line dead where (2008) zone there in alsoturbulent is the disks. suggest a disk that jump mid-plane in mm-sized surface (Johansen grains density can (Brauer clump et in al. the 2008). region Cuzzi between small eddies in c Swinburne University of Technology, 2011 51 OF 44 AGE P . Once this size, the planetesimals are decoupled from the gas and move on HET620-M09A01:Evolution Planet Formation: Disk Formation and While the mechanism is notplanetesimals yet fully understood, theKeplerian grains orbits will around eventually the become proto-Sun. kilometre-sized important. Mutual gravitational interactions and collisions then become The solar nebuladifferent would orbits with have a contained range ofcollisions an eccentricities did and enormous occur inclinations. While and number theyhave close would of resulted encounters be in widely gravitationally planetesimals, separated, altered growth, all theirdestruction. while orbits. on fast collisions slightly Slow would collisions have would resulted in their fracture and c Swinburne University of Technology, 2011 51 OF 45 AGE P , the esc v < v . 4 R , each several hundred kilometres in size. Eventually, where larger bodies grow much faster than smaller bodies, , then the planetesimal growth rate is proportional to the square of esc v ≥ v Credit: P. Rawlings (Courtesy NASA/JPL-Caltech) . When the impacting velocity is smaller than the escape velocity, 2 runaway accretion R HET620-M09A01:Evolution Planet Formation: Disk Formation and The more massive planetesimals havealmost a everything larger in gravitational their collisionvelocity path. cross-section of so the can As larger accrete longthan planetesimals, as the they escape the velocity, can impacting growthe velocities very grain are rapidly. size, smaller If thanplanetesimals the the grow impacting much escape velocity faster with is their larger growth rate proportional to This leads to a resulting in planetary embryos, or the protoplanets will accrete everythingthen within ends. their gravitational reach and the rapid growth phase c Swinburne University of Technology, 2011 51 OF 46 AGE P years. 6 to a few 10 5 . The large size jump in the size of protoplanets at the Mars-Jupiter boundary Earth HET620-M09A01:Evolution Planet Formation: Disk Formation and In the inner Solarmetals System, and protoplanets rocky were materials. the1 size and In of the 15 asteroids outer M and Solar small System, , protoplanets made up grew of much larger, between After about a millionphotoevapotation. This years, puts the strong time nebula constraintshuge began on the to are formation of clear made themust through up giant have planets, of a formed since within gas combination their a from million of the years. solarThe solar wind nebula. protoplanetsand continued Therefore, to thesolids cores grow in of slowly the the via disk. giants formed gravitational planets in collisions, After stable orbits, clearing about asbelt 10–100 up well objects as million the(which some includes years, remaining remaining ). debris the - the Solar asteroids, System comets and wasKuiper made, with 8 newly was due to the availabilityof of materials. volatiles than Since the metalsthe solar and nebula outer silicates, contained Solar a this much System, meantprotoplanets higher is that resulting proportion thought there to in be was much a much few larger 10 more protoplanets. material available The in formation timescale for the c Swinburne University of Technology, 2011 51 OF 47 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and We have discussed how protoplanetaryas disks a form natural from by-product aon rotating of a collapsing the viscous molecular star cloud timescale, formation core transferring slowly angular process. moving momentum material outwards. Once We inwards formed, discussedturbulent to various protoplanetary viscosity help sources of disks due build disk the evolve to viscosity,which including growing convection proto-Sun produce and while MHD spiral turbulence, waves,eventually gravitational and disperses, torques magnetic with in some torques massiveaway material that by disks the accreting results solar on wind, in and the magnetic most proto-Sun, materialBut breaking. being some before the photo-evaporated. material disk disperses, The being some disk ofthe blown the various material stages must go of into grain forming growth,large the which planets. depend grains We on talked about the grow graincondensation via size: sequence tiny in collisions, grains the stick disk and electrostatically, determines planetesimals theIn initial and chemical the gradient next protoplanets in Activity the we grow dust. detail. will via look at accretion. the final process The of terrestrial and giant planet formation in more Summary c Swinburne University of Technology, 2011 51 OF 48 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Acton, G., et al.and (2007). Meteorites: “Magnetic Insights Fields fromMeasurements”, of LPI, Magnetic the 38, Remanence Early p1711 and Solar First-Order System Reversal RecordedBalbus, Curve in S.A. (FORC) Chondrules & Hawley,disks. J.F. I (1991). - Linear “A analysis. II powerful - local NonlinearBerg, shear evolution”, ApJ, T., instability 376, et p214 in al.Implications weakly for magnetized Nebular Cooling (2009). Rates “, ApJ, “Direct 702,Blum L172 Evidence et for al. CondensationProperties in and (2006). the Relations to Early Primitive “The Bodies Solar in Physics System theBlum of Solar and System”, & Protoplanetesimal ApJ, Wurm 652, Dust p1768 (2008).Disks”, Agglomerates. ARAA, 46, 21 I. “The Mechanical Growth MechanismsBrauer, of F., et Macroscopic al. Bodiesprotoplanetary in (2008). disks”, A&A, Protoplanetary 487, “Planetesimal L1 formation nearCrutcher, the R.M. snow (1999). line “Magnetic inApJ, Fields MRI-driven 520, in p706 turbulent Molecular Clouds: Observations ConfrontCuzzi, Theory”, J. N.,”, et ApJ, 87, p1432 al.Evans, (2008). N. J.Efficiencies; et “Toward Evolution and al. Planetesimals: Lifetimes”, ApJS, 181, (2009). p321 Dense “The Clumps Spitzer in c2d Legacy the Results: Star-Formation Rates and • • • • • • • • • References c Swinburne University of Technology, 2011 51 OF 49 AGE P O Enrichment from the Inner Rim of the Solar 16 ¨ uttler, C., et al. (2010). “The outcome of protoplanetary dust growth: pebbles, boulders, or HET620-M09A01:Evolution Planet Formation: Disk Formation and Gammie, (1996). “Layered Accretion in T Tauri Disks”,Gorti, ApJ, .457, U. p355 et al. (2009).by “Time, Far- Evolution Extreme-Ultraviolet, of Viscous and Circumstellarp1237 X-ray Disks Radiation due to from Photoevaporation the CentralGreaves, Star”, J. ApJ, and Holland, 705, W. (1999).302, L45 “Ambipolar diffusion in magnetized cloud cores”,G MNRAS, planetesimals?. I. Mapping the zoo of laboratory collisionHaisch, experiments”, K.E., A&A, et 513, al. 56 (2001). “Disk Frequencies andHollenback, Lifetimes D. in & Young Clusters”, Adams, ApJ, F.C. (2004). 553,Kuiper L153 Belt “Dispersal Formation”, of Disks ASP Aroundp168 Conference Young Series Stars: 324 Constraints (ed. on Caroff, Johansen,, A., Backman & et Praton), al., 448, p1022 (2007). “Rapid planetesimalLiffman, formation K. in turbulent & circumstellarprotostellar Brown, accretion disks”, M. disk”, Icarus, (1995). 116, p275 “TheLiffman, motion K. and (2010). size “Particle sorting Formation of and particles ejected from a Nebula”, LPI, 41, 1135 • • • • • • • • • c Swinburne University of Technology, 2011 51 OF 50 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Lynden-Bell, D. and Pringle, J.nebular E. variables”, (1974). MNRAS, 168, “The p603 evolution of viscousMarvin, discs U. and B., the et origin al.Science of Letters, (1970). the 7, p346 “Ca-Al rich phases inMcKee, the C. allende F. and ”, Ostriker, E. Earth C. and (2007). Planetary “TheoryMestel, of L. star and formation”, Spitzer, ARAA, L. 45, (1956). p565 “Star formationMouschovias, in magnetic T. dust Ch. clouds”, MNRAS,magnetic 116, (1976). interstellar p503 clouds embedded “Nonhomologous inApJ, contraction an 206, intercloud and p753 medium: and equilibria Star ApJ, formation” of 207, (papers p141 self-gravitating, IPignatale, & II), F. et al.protoplanetary dust”, (2011). MNRAS, 414, p2386 “The effect ofShu, F.H., the Adams, F.C. regular and Lizano, solution S.and (1987). model theory”, “Star in ARAA, formation 25, the in p23 molecular condensation clouds of - Observation Velusamy, T., et al. (2002).L1157”, “Tracing ApJ, the 565, Infall L43 and the Accretion Shock in the Protostellar Disk: • • • • • • • • c Swinburne University of Technology, 2011 51 OF 51 AGE P HET620-M09A01:Evolution Planet Formation: Disk Formation and Weidenschilling, S. J. (1977a). “Aerodynamics ofp57 solid bodies in the solar nebula”, MNRAS, 180, Weidenschilling, S. J. (1977b).nebula”, Ap&SS, 51, “The p153 distribution of massYorke, in H. the planetary W.intermediate-mass system stars”, et ApJ, and 443, al. solar p19 Zolensky, (1995). M. E.,Samples”, et Science, “The 314, al. p173 formation (2006). of protostellar “Mineralogy disks. and Petrology of 2: Comet 81P/Wild Disks 2 Nucleus around • • • •