Characteristic Properties- Solar System 1. Planets isolated in space=cleared orbit 2. Disk shape of solar system- small orbit inclination; prograde circular motion; same tilt&direction of rotation axes (almost) 3. Jovian/Terrestrial planets: low/high density, huge/small atmospheres, fast/slower rotation rates, many/few moons & rings 4. Space Debris icy comets, rocky asteroids, meteoroids, Kuiper Belt 5. Common ages of Earth, Moon, Mars, meteorites, Sun
Tidal=Passing Star Hypothesis Buffon in 1745 Catastrophic process Low probability of encounter Hot gasses would dissipate before they could condense Predicts few stars with planets
Nebular Theory Descartes 1644 envisioned vortices Laplace 1796 added Newton s gravity Evolutionary process Sun and planets formed from a vast rotating cloud of gas and dust called the solar nebula
Solar Nebula All the stars form from dust clouds Most dust &gas falls on Protosun Cloud is spinning so dust falls in faster along poles forms protoplanetary disk Lumps in disk become planets Predicts the many stars with planets
Protoplanetary Disks =Proplyds Sun & planets clean out inner disk ending planet building 2MASS and Gemini AO observations of binary star with disk 5 disks in Orion Nebula
NOT evidence that the planets formed in a disk surrounding the Sun is: a) The planets orbits are inclined only a few degrees to the equator of the Sun (=ecliptic) b) The planets all orbit in the same direction as the Sun rotates c) We see protoplanetary disks around other stars in star formation regions d) We see many extrasolar planets as predicted by the Solar Nebula Theory which includes disks e) The Solar Nebula Theory by Laplace & Descartes
Kepler-56 Has 2 planets not in equatorial plane of star Companion star pulls on planets & misaligns them
Protosun Most of the material fell to the centre of the Solar Nebula forming the Sun in ~100 Million years Becoming a star with hydrogen fusion in its core
Condensation Theory Shuttle experiment done in no gravity found dust forms grains very quickly around condensation nuclei A layer of atoms condenses at a time to form snowflakes
Hot Disk and Frost Line (Snow Line) Gas & dust in solar nebula heated by protosun Nebula is hotter closer to sun and colder in outer orbits Beyond frost line, H 2 O forms snowflakes & Jupiter
Condensation Temperature Metals freeze out first, then rock, then ices Planets close to sun form from metals, then rocks, then ice Density of planets goes from dense to less dense Terrestrial to Jovian
Accretion Gradual growth by collision & sticking Snowflakes become snowballs
Planetesimals Eventually massive enough to grow by gravity A few kilometers in size Pandora & Hyperion; Low density moons of Saturn
Protoplanets The more massive they are the more planetesimals they collect; the faster they grow At more than 15 earth masses gravitational collapse starts Capturing Hydrogen and Helium directly from nebula
Core-Accretion / Gravitational Instability Model Disk blown away by sun and other stars in a few million years Core accretion model= (Iron+rock+ice) core then gas too slow Disk Instability=Density enhancement draws in gas directly from disk Movie by Phil Armitage 2005 shows density waves excited by planet
Migrating Planets Encounters with planetesimals sweep/ eject planetesimals into asteroid belt, Kuiper belt, Oort cloud Move Jovian planets out/in depending on if they pass in front or behind planet
Planetary Migration Jupiter and Saturn may have formed much further from Sun & moved in Uranus and Neptune moved further out from Sun
Fragmentation High speed collisions between protoplanets & planetesimals creates a debris disk P/2010A2 comet? Collision of 2 small asteroids
Debris Disk Not the dense protoplanetary disks that form planets Cold debris disks are left Made from asteroid, comet, planetesimal collisions
Large Impacts In final stages a planet would have had many collisions with bodies the size of planets Such impacts could tilt the rotation axis of Uranus, Pluto + rotation speed of Venus Solar system is like a full coffee cup some coffee probably got spilled
Processes That Cleared the Inner Solar System Radiation pressure from sun&stars Protosun s wind (&stellar) blows away gas & dust Planetesimals incorporated into planets or ejected All done in millions of years
Overview of Planet Formation Common orbital and rotation direction & plane =>protoplanetary disk Jovian / Terrestrial => range of temperatures in disk / frost line Interplanetary debris left over from formation = asteroids, comets, Common ages => simultaneous formation in disk Collisons of protoplanets = irregularities in Solar System
The main reason terrestrial planets are more dense than Jovian planets is: a) The Jovian planets migrated thru the disk more b) The Jovian planets formed outside the frost line c) The less dense compounds rose to the outer orbits d) The solar wind blew away the terrestrial planet s less dense elements e) The protosun absorbed all the less dense elements in the inner solar system so none were left for the terrestrial planets
Chemical Differentiation of Planets Young planet very hot due to impact heating (=heat of formation) +Radioactive decay in core of planet Iron, Nickel, Iridium settle to the core Silicates rise above iron Ices/water next
Outgassing Water, carbon dioxide, sulfur dioxide, nitrogen released by volcanoes Forms atmosphere
Angular Momentum Problem The protosun rotates rapidly and has huge convection cells so it generates a strong magnetic field The magnetic field tries to accelerate the disk and solar wind, slowing rotation by magnetic braking Observations of stars with known ages in Hyades etc. show that the older stars rotate more slowly
Late Heavy Bombardment Late Heavy Bombardment second surge in impacts When Jupiter, Saturn, Uranus, Neptune change orbits scattering planetesimals?
MOST: Jaymie Matthews UBC Observed HD209458 for months and Saw no eclipses from Earth sized planets Timed transits showing no Earth sized planets-so far No opposition effect so low 50% albedo
Comet Lulin Dirty Snowball or Icy Mudball Nucleus ~10km Tail ~1 million km 3572 comets 2000 short period
Comet NEAT 29Jan & 2Feb03 Dirty snowball or maybe icy mud ball is better Nucleus ~ 10km Tail ~1,000,000km to 1 astronomical unit Very eccentric elliptical orbit
Coronographic Image of Debris Disk Star is masked by black spot in original and untilted image Notice cleared inner disk(30au) and spiral wave features ~320 light years distance, 300AU diameter, 5 Million years old
Gravity Assist Throws ball on parked car Throws ball on moving car Throws ball on orbiting car
Impact Crater Formation Impactor has velocity 10 times rifle bullet Releases energy 10 times equal mass of dynamite Impactor vaporized when temperature reaches millions K Shock wave forms shocked quartz found only in impacts Rebound can launch rocks without destroying them
Rocky Surfaces Saturated with Craters Planets formed from many meteorite impacts Circular craters due to explosion caused by impact Solar System Full?
Erosion of Craters Craters hidden by: 1. Volcanoes lava flows 2. Continental drift 3. Erosion by atmosphere 4. Oceans
Younger Terrain = Fewer Craters The larger the terrestrial world; the more internal heat it will retain = higher temperature in core The higher temperature; more geologically active so more craters are covered = fewer craters showing Older terrains = more craters
Comet Impacts on Jupiter Painting shows Jul94 impacts of Comet Shoemaker-Levy 9 HST photo from 20Jul09 Comets deposit ice Heating planet
03Jun10 Jupiter Impact Last June Jupiter became a little more massive Two amateur astronomers recorded the impact 2009 impact left scar Notice missing SE belt
Planetary Magnetic Fields Jovian planets plus Earth have magnetic fields Various directions and strengths and offsets
Planetary Dynamo Conducting, convecting/circulating, rotating core generates magnetic field Earth: Iron core; Jupiter: liquid metallic hydrogen Uranus, Neptune: water with ions
Magnetometer Measures the strength & direction of Magnetic field Can probe the interior of the planet
Elemental Abundances Element determined by number of protons=atomic number Neutrons determine Isotope Elemental abundances on Earth Not the same as in stars, Jupiter, Saturn
Elements Forged In Star s Cores You are made of star dust Stars have died so you may live
Chondrules Many meteorites contain small glassy inclusions Formed by rapid melting and solidified in hours Chondrules date from formation of Solar System