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Solar System Formation Lecture Overview Inventory of the Solar

Lecture Overview Formation

Karen J. Meech Hsin-Fang Chiang

• Our Solar System • Formation of our planets • Inventory • ISM – starting material • Architecture • Standard Model • What formation models need to • Our solar system compared to explain others – what does not work in standard model

X-rays Inventory of the Inventory of the Solar System Solar System Far UV • 4 Terrestrial – “rocky” Planets

Visible (H-!)

Infrared

Solar Wind Planet a e i Diam "# mass pv TBB 3 [AU] [deg] [km] [g/cm ] [MEarth] [K] • 1 Star Mercury 0.38 0.21 7.00 4878 0 5.43 0.06 0.12 442 • TBB ~ 5700K Venus 0.72 0.01 3.39 12104 0 5.24 0.82 0.75 232 • Provides heat and EM radiation Earth 1.00 0.02 0.00 12756 1 5.52 1 0.39 254 • Flow of charged particles (solar wind) Radio (5GHz) Mars 1.52 0.09 1.85 6794 2 3.9 0.11 0.25 210

Inventory of the Solar System Inventory of the Solar System

• 4 Terrestrial – “rocky” Planets • 4 Terrestrial – “rocky” Planets

Planet a e i Diam Moon " # mass pv TBB Planet a e i Diam Moon " # mass pv TBB 3 3 [AU] [deg] [km] [g/cm ] [MEarth] [K] [AU] [deg] [km] [g/cm ] [MEarth] [K] Mercury 0.38 0.21 7.00 4878 0 5.43 0.06 0.12 442 Mercury 0.38 0.21 7.00 4878 0 5.43 0.06 0.12 442

Venus 0.72 0.01 3.39 12104 0 5.24 0.82 0.75 232 Venus 0.72 0.01 3.39 12104 0 5.24 0.82 0.75 232

Earth 1.00 0.02 0.00 12756 1 5.52 1 0.39 254 Earth 1.00 0.02 0.00 12756 1 5.52 1 0.39 254

Mars 1.52 0.09 1.85 6794 2 3.9 0.11 0.25 210 Mars 1.52 0.09 1.85 6794 2 3.9 0.11 0.25 210 Solar System Inventory of the Solar System Inventory

! 4 Gas Giant Planets Itokawa

• Thousands of • Orbit between Mars & • Largest, (diameter=913 km) Planet a e i Diam Moon " # mass pv TBB 3 [AU] [deg] [km] [g/cm ] [MEarth] [K] Jupiter 5.20 0.05 1.31 142,796 67 1.3 318 0.34 110

Saturn 9.54 0.06 2.49 120,000 62 0.7 95.2 0.34 81

Uranus 19.19 0.05 0.77 52,400 27 1.3 14.5 0.30 58 Mathilda 30.06 0.09 1.85 50,450 13 3.9 17.1 0.29 46 Eros Gaspra Ida & Dactyl

Inventory of the Solar System Selected Solar System

• 186 satellites of planets • Some are as big as planets • Some are of interest for astrobiology Mercury • Some have atmospheres • Some may be captured “debris” Io (Jupiter) Titan ()

Europa (Jupiter)

Miranda (Saturn) (Neptune) Phobos (Mars)

Inventory of the Solar System Large Objects

• Icy Left overs from planet formation • Search for Planet X Name Albedo Diam [km] • Comets, Centaurs, KBOs, Dwarf Planets • Perturbations in orbit lead to 2003 UB313 0.86 2400+/-100 discovery of Neptune 0.6 2390 • Spurred search for “Planet X” – Pluto was discovered 2/1930 by C. Tombaugh 2003 EL61 0.6 1200? • Size too small to affect the orbits of 2005 FY9 0.6 1250? Uranus/Neptune • Should the Solar System end? Charon 0.4 1270 • 1990’s outer SS surveys " Kuiper belt Sedna 0.2? 1500? 2004 DW 0.04 1500 Quaoar 0.12 1200±200 Ixion 0.09 1065±165 2002 AW197 0.1 890±120 Varuna 0.07 900±140 Is Pluto a Planet? Planets versus Brown Dwarfs?

• International Astronomical Union Planet Redefined (2006) • Must orbit the • The large end of planets: • Must have sufficient mass to attain hydrostatic equilibrium (round shape) • Must clear the neighborhood of its orbit • Up to 13 Jupiter masses " then can burn deuterium • Pluto is now a “dwarf planet” (or historical planet)

Asteroids as of 2/18/2013

Inventory of the Solar System Solar System Architecture

• From Comets and • Outer Solar System collisions • Kuiper belt – flattened disk beyond Neptune ~ 30-50 AU • Cosmic dust • – spherical cloud to ~100,000 AU

1 micron • Inner Solar System (~100,000) • (green) • From the Sun • Near Earth Objects (red) • Comets • solar wind (mostly protons, electrons and He nuclei)

• Cosmic rays Inner solar system • energetic charged particles animation – 2 yrs • Heavier atomic nuclei

Questions to Answer: Composition

• Why are terrestrial planets different from Solar System Characteristics to Jovian planets? Explain with Models

18 Questions: Planet Scale / Solar Questions to Answer: Moons System Perspective • Why do planets have satellites (Moons)? • Why do planets orbit in a plane vs. a sphere? • Why do satellites resemble mini solar systems? • Why do planets orbit the sun in same direction? • Why do comets orbit with random inclination and direction? • Why are planetary orbits nearly circular?

Questions: Obliquity Questions: Volatile Inventories • Obliquity • The tilt of the rotation axis to the plane of the orbit. • Comets are icy leftovers (volatile rich) • Planets rotate prograde with obliquities < 29° • Volatile – melt / sublimate at low T • Exception: Uranus • Refractory – melt / sublimate at high T • Exception: Venus rotates retrograde (backwards) • How did reach inner planets? • How do we explain the asteroid belt?

Starting Materials: The Interstellar Medium • Composition • Dust Forming Our Solar System • Gas • Cosmic rays

Where kg m-3 m-3 Distance [m] Air 1.2 1025 10-9 Vacuum on Earth 10-9 1018 10-6 Orion Nebula 10-18 109 10-3

-28 24 Intergalactic Space 10 0.1 2 Star Forming Where are stars born Environment • Molecular clouds – Initial Conditions • T ~ 10-30 K • Dense gas/dust shield their contents against UV • Balance between pressure & gravity • External trigger initiates collapse of cloud cores? • Super novae? • Collision between clouds

• Most stars form in clusters (multiple star systems) • Stellar wind, UV from neighbors can erode gas / dust disk • Can impart a chemical fingerprint on the system

Gravitational Collapse & Disk Formation What is your physical intuition – what shape does a spinning sphere collapse into?

A – • Cores collapse under their own mass • Once dense enough, radiation cannot easily escape – Temperature increases B –

What happens if the core is rotating? C –

D – ?

Gravitational Collapse & Disk Formation Disk Collapse & Observations conservation • HST image of • Flattened disks at start of collapse • If fall perpendicular to spin axis • Age < ~ 100,000 years • Needs to speed up • Resistance centrifugal force

• If fall parallel to spin axis • No resistance • Forms a • Collisions cause grains to lose energy - • Collapse proceeds faster in center " flattening in core They will continue to collide until they cannot • Loss of energy through collisions • Origin of planet’s orbits • Densest near core and near mid-plane • Temperatures increase near center Planet Growth Grain Formation

• Dust Settles to mid-plane • Micron-sized grains • Collisional aggregation • Random collisions and sticking • Temperature gradient in disk, disk heats toward center " vaporizing many of the • Gravitational focusing: Runaway growth starting materials. • Planetary embryos • 1500K refractories Ca, Al • Sweep up its neighboring region • 1300K abundant refractories Mg-Si, Ni-Fe alloys • 500K chemical reactions graphite, C-rich • Core-Accretion • 200-500K hydrated minerals hydrated minerals • Cores of jovians grow large enough to • <200K H2O ice + others CO, CO2, CH4, NH3 accrete gases • Materials condense out as small grains • Acquire mass locally – composition depends • Composition varies with distance from the sun (the “snowline”) on where they are formed

Alternate model for Jovians: Comet Formation Gravitational Instability

• Begin as icy • Core Accretion model problems • ejection of icy plane- • Lifetime of gas disk is shorter than time tesimals needed to form core (millions of yrs) • Inward: volatiles to inner planets • Gas/dust disk instability model • Outward: formation of Oort cloud • Accounting for gravity, radiation transfer and heat • Disk breaks into clumps • Clumps contract into a core • Occurs on timescales of 1000’s of years Formation of Asteroid Belt? Gravitational stirring near Jupiter’s orbit

Summary of Planet formation

• Initial stages • Collapse of molecular cloud • Formation of central star Evidence Supporting our • Rotation of solar nebula • Nebula cooling and coagulation of Models small dust particles to larger objects • Planetary Building blocks • Formation of planetesimals • Growth to protoplanet size • Formation of planets • Re-arrangement of solar system • Possible migration of planets

38 Early Condensates: CaIs Evidence of Sweep up: Collisions

• Calcium-Aluminum inclusions – high T ! Chondrules • Formed close to sun ! Impact melt from early collisions • Moved outward into disk via a wind ! Craters • Radioactive dating gives us time zero “ ” ! Tell us that things were being hit – final • Meteorites and grains are being used to give a build up of planets chronology of the solar system formation

Answering the Questions Answering the Questions

• Chemical differences between • Prograde rotations, small obliquities terrestrial / Jovians • Angular momentum • T condensation / snow line • Exception: Uranus obliquity • Co-planar circular orbits in same • Collisions? " cannot explain satellite planes direction; • Dynamical interaction? • Momentum / min E state • Exception: Venus, Mercury Rotation • Formation of Asteroid Belt? • Venus rotates retrograde (backwards) • Gravitational stirring near Jupiter’s orbit • Mutual dynamical interactions

The The “Nice” Model

• Late Heavy Bombardment – LHB N • ~700 My after formation " chronology of lunar samples U U • NICE Model Dynamical Scenario N • Departure of gas disk (100My) S S • Jupiter, Saturn orbits evolve J J (interact with disk) • When cross 2:1 MMR (mean motion resonance) (PSat/PJup=2) " orbits become eccentric (cross others) • Outer Solar System destabilized • Bombardment begins 779-882 My • 200My later –3% disk mass left J S N U What Can the “Nice” Model Explain? Satellite Formation

• Reproduce Jovian planet orbits • Different scenarios (e, i) • Earth – embryo impact • Reproduce Jupiter & Neptune orbits • Mars – capture of asteroids • Accounts for Embedded icy • Giant Planet Satellite Systems bodies in asteroid belt • Reproduces KBO orbits • One possibility mini-solar nebula or • Explains the LHB • Captured objects

• 1.8x1023 g comet water to Earth • 6% ocean mass – where did the rest come from?

Callisto Complications Large Satellite Systems Europa • Over 1000 extra-solar planets have been discovered to date Io Ganymede

• Galilean Satellites • " decreases with Jupiter distance • Long timescales • Formed with nebula as it grew • Small irregular satellites • Collisional families

Extra Solar Planets Beyond the Standard Model

• Extrasolar planetary systems do • Planet-Disk gravitational interaction not have our architecture. • Planets migrate toward central star • Gas giants very close to star • Planet experiences drag as moves through dust • Planets on non-elliptical orbits • Loses energy " orbit gets smaller • Why? • Timescales < 1 Myr Summary Planet Formation in Binary and multi-star systems with planets • InventoryBinary and architecture and multi-star ofsystems with planets Multiple Systems? our Solar System • Terrestrial planets vs. • Over half of the stars are binaries Jovian planets • ~20% of extra solar planets are in • Comets & primitive bodies • Flattened disk, circular orbits binary or multiple star systems HD188753 HD188753

• Formation of our planets • Protoplanetary disk GJ 86 : Separation ~ 20 AU 4 Jupiter-Mass Planet @ 0.11 AU • Temperature gradient • Planet growth $ Cephei : Separation ~ 18.5 AU 1.67 Jupiter-Mass Planet @ 2.1 AU • Beyond our Solar System

HD188753 : Separation ~12 AU • Extra-solar planets 1.06 Jupiter-Mass Planet @ 0.67 AU

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