Light & Origin of the Solar System Read: Chapters 5: “Light” Reading. Chapter 8: First 10 pages only. Homework Due Tomorrow (Friday). © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Last Time: Light © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Last Time: Light as a Wave f is frequency  is wavelength For light: f  = c c = 300,000 km/s Our eyes recognize f (or ) as color . © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Last Time: Light as a particle Light as photons Each Photon Has an Energy: E = hf © 2005 Pearson Education Inc., publishing as Addison-Wesley

Emission of Light by Atoms or Molecules Last Time: Emission of Light by Atoms or Molecules Atoms and Molecules have Distinct Energy Levels Excited atoms & molecules change from high to low, photons emitted © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Energy Levels of Atoms Electron is allowed to have certain energies in an atom. Electrons can absorb light and gain energy or emit light when they lose energy. Hydrogen Atom Consider light as a photon when discussing its interaction with matter. Only photons whose energies (colors) equal the difference in electron energy levels can be emitted or absorbed. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Absorption of Light by Atoms & Molecules Atoms absorb photons whose energies (i.e. wavelengths) match the energy difference between two levels in an atom. The resulting spectrum has all wavelengths (all colors), but is missing wavelengths that were absorbed. You can determine which atoms are in an object by the emission & absorption lines in the spectrum. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Warm, Opaque Objects Glow by Thermal Emission of Light Cool Warmer Hot Hotter Red & Faint White & Bright © 2005 Pearson Education Inc., publishing as Addison-Wesley

Warm, Solid Objects Glow by Thermal Emission of Light Cool Warmer Hot Hotter Red & Faint White & Bright © 2005 Pearson Education Inc., publishing as Addison-Wesley

At Infrared Wavelengths Thermal Emission At Infrared Wavelengths Dog © 2005 Pearson Education Inc., publishing as Addison-Wesley

Warm, Solid Objects Glow by IR Thermal Emission of Light Brighter ==> Warmer Human skin is an emitter of infrared “thermal” radiation with wavelengths greater 3 microns. This energy may be recorded to yield a quantitative temperature map of the skin. The skin temperatures are determined mostly by the flow of blood nearby and by the heat conducted from within the body. An image in the infrared yields information about pathological conditions within the body. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Thermal Emission from the Earth 6 x 10-8 x T4 (T in degrees Kelvin) Flux = © 2005 Pearson Education Inc., publishing as Addison-Wesley

“Thermal Emission” from Warm, Opaque Objects 1. Warm objects emit Infrared light and radio waves Examples: Warm embers of fire, electric stove. 2. Hotter objects emit more light energy per unit surface area (per second). (Energy emitted per sec increases as Temp4 ) 3. Hotter objects emit bluer photons (with a higher average energy.) average increases as 1/ T (using kelvin Temp scale) © 2005 Pearson Education Inc., publishing as Addison-Wesley

Warm, Solid Objects Emit Light: “Thermal Emission” Examples: Electric Stove Filaments Fireplace Coals Light bulb filament Warm human body © 2005 Pearson Education Inc., publishing as Addison-Wesley

“Thermal Emission” from Opaque Objects Hotter objects emit more light energy per unit surface area per second. Energy emitted = 6x10-8 T4 (Joules per m2 per sec) Hotter objects emit bluer photons (with a higher average energy.) “Wien Law” max = 2900 m / T (T in degrees Kelvin) © 2005 Pearson Education Inc., publishing as Addison-Wesley

Light carries information about the Planets and Stars Key: Separate light into its different wavelengths (spectrum). By studying the spectrum of an object, we can learn its: Composition Temperature Velocity © 2005 Pearson Education Inc., publishing as Addison-Wesley

Spectrum from a Typical Planet, Comet, or Asteroid Reflected visible light from Sun Thermal Emission (IR) Absorption by molecules in gases in atmosphere Spectrum reveals: Chemical Composition Temperature Velocity © 2005 Pearson Education Inc., publishing as Addison-Wesley

. Formation of the Solar System Section 1 Clouds of Gas and Dust in the Milky Way Galaxy © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Overall Properties of our Solar System Circular Orbits (elliptical, but nearly circles) All planets lie in one flat plane (the Ecliptic). They orbit & spin in same direction (counter clockwise) Inner Planets: small, rocky Outer Planets: large, made of gas and ice How did our Solar System Form ? ? ? © 2005 Pearson Education Inc., publishing as Addison-Wesley

The Origin of the Solar System Four characteristics of our Solar System must be explained by a formation theory. What is the basic idea behind the theory? © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Interstellar Gas and Dust in our Milky Way Galaxy Light absorbed from distant stars along mid-plane. Dust and Gas In Interstellar Clouds ! © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Dark Clouds in the Milky Way Milky Way Centaurus A HST © 2005 Pearson Education Inc., publishing as Addison-Wesley

The Interstellar Medium (ISM) Dust & Gas The Interstellar Medium (ISM) © 2005 Pearson Education Inc., publishing as Addison-Wesley

Dark Clouds in our Galaxy Dense gas and dust. 1% (by mass) is “rocky/icy” dust particles that could eventually make terrestrial planets. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Absorptionof Light by Dust Dust clouds: Opaque in visible (“Optical”) light. Lower opacity in infrared. Dust scatters visible light more efficiently than infrared ==> To Study the Milky Way Galaxy: use IR ! Visible Light Infrared Light © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Gas Clouds contain hydrogen, helium, carbon,nitrogen, oxygen and complex molecules © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Dust is Made of Atoms Small Dust particle: Only a few thousand atoms © 2005 Pearson Education Inc., publishing as Addison-Wesley

Large Dust Particle: 10,000’s of Atoms! Interstellar Dust Grain: C, O, Si, H20 ice, Si-O. © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Basic Observation Stars are continuously forming in the galaxy. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Dense Clouds Floating in our Milky Way Galaxy Gravity pulls atoms closer together © 2005 Pearson Education Inc., publishing as Addison-Wesley

Collapse of the Solar Nebula © 2005 Pearson Education Inc., publishing as Addison-Wesley

A Young Star Forming, surrounded by a protplanetary disk Artists Rendering A Young Star Forming, surrounded by a protplanetary disk © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Cloud Contracting Due to Self-Gravity As the nebula contracts due to its self-gravity, it heats up, spins faster, and flattens. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Flattening of the Solar Nebula As the nebula collapses, clumps of gas collide & merge. Their random velocities average out into the nebula’s direction of rotation. The spinning nebula assumes the shape of a disk. © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley

Protoplanetary Disks… Star and planet formation Protoplanetary Disks… Solar System size Measured Sizes: 100-1000 AU Masses: 10-3 – 10-1 Msun © 2005 Pearson Education Inc., publishing as Addison-Wesley

Formation of Planetary Systems Observations  Models of Planet Formation Protoplanetary Disks of Gas & Dust Observations Thermal Emission (Infrared) from Dust Hubble Space Telescope Pictures of protoplanetary disks.  Mass of Disk = 10-100 MJUP Disk Lifetime ~ 3 Million years Theory of Planet Formation: Dust collides, sticks and grows  pebbles/rocks Gravity helps attract more rocks Gravity attracts gas © 2005 Pearson Education Inc., publishing as Addison-Wesley

Theory of Rocky Planet Formation Inward of 2 AU Planetesimals (km-sized comets & asteroids) Growth of rocks (planetesimals) by collisions and sticking together Friction circularizes orbits Big planetesimals gravitationally stir small rocks Mergers among planetesimals: They grow to Earth-Size Analytical and N-body: Lissauer 1987 Rafikov 2003 Chambers, Thommes 2002 Goldreich, Lithwick, Sari 2004 Safronov 1969 Greenberg et al 1978 Wetherill & Stewart 1993 Kokubo & Ida 2000 © 2005 Pearson Education Inc., publishing as Addison-Wesley

Building the Planets Inward of 3 AU At 3 AU is “Snow Line” : Hotter than 0C Only rocks & metals condensed inward. Too hot for gases (H, He) to stick to rocks. Hydrogen compounds (H2O, NH3, CH4 ) are gases.  Only rocky planets inward of 3 AU. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Building the Planets Beyond 3 AU - Cold! - Hydrogen compounds (ices, H2O, NH3, CH4) condensed. - Planetesimals made of ROCK and ICE ! Gases (H, He, hydrogen compounds) gravitate to rocks:  Form Planets made of rock, ices, and gases! Jupiter, Saturn, Uranus, Neptune © 2005 Pearson Education Inc., publishing as Addison-Wesley

© 2005 Pearson Education Inc., publishing as Addison-Wesley Building the Planets accretion -- small grains stick to one another via electromagnetic force until they are massive enough to attract via gravity to form... © 2005 Pearson Education Inc., publishing as Addison-Wesley

Building the Giant Planets Gas-giant planets form by gravitationally attracting H and He gas. More gas acquired: More gravity. Attraction of Gas is a “runaway” ! Jupiters form their own “miniature” solar nebula. Moons formed out of the mini-nebula. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Summary: Origin of the Solar System Theory – our Solar System formed from a giant, swirling cloud of gas & dust. Depends on simple principles of Physics: Dust particles collide, stick together & grow. Law of Gravity: gravitational attraction of particles and gas Conservation of angular momentum to flatten the protoplanetary disk. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Theory Explains: Orderly Motions in the Solar System The Sun formed in the center of the gas-dust protoplanetary disk. The planets formed in the protoplanetary disk. This explains: all planets lie along one plane (in the disk) all planets orbit in one direction (the spin direction of the disk) the Sun rotates in the same direction the planets would tend to rotate in this same direction most moons orbit in this direction most planetary orbits are near circular (viscous smoothing of orbits) © 2005 Pearson Education Inc., publishing as Addison-Wesley

Origin of the Solar System Our theory explains the properties of the Solar System Planets in orderly motions: circular orbits, flat plane, orbit same direction. There are two types of planets. small, rocky terrestrial planets large, hydrogen-rich Jovian planets Asteroids & comets exist in certain regions of the Solar System © 2005 Pearson Education Inc., publishing as Addison-Wesley