of Origin the Solar System ASTR 121 Sarazin
Our Solar System in Earlier Days?
Test 2
Wednesday, April 9, 2008 In Class (will take entire 50 minutes) Will be Multiple Choice, Short Answer, Fill In the Blank questions No essay questions No complicated math problems You may not consult the text, your notes, or any other materials or any person Bring pencils (test on scantron sheets)
Origin Facts to be Explained
Orbits
All in single plane = equator of Sun All revolve same direction (same as Sun rotation) Most orbits nearly circular Regular spacing (Bode's law?)
Rotation of Planets
Terrestiral Jovian
Most prograde = same direction as orbit Composition vs. distance from Sun
Terrestrial = dense rock = near Sun Jovian = less dense, gas, H, He = far from Sun
Origin Facts to be Explained
Ice Worlds
Comets Kuiper Belt Oort Cloud
Asteroids, Meteorites Cratering of planetary surfaces Age of planets = age of Sun = 4.6 billion years Sun rotates slowly?
Irons, Stones
Origin of Solar System
Originally, two theories Catastrophe Theory
Planets formed due to collision of Sun with another star
Nebular Theory
Planets form as normal part of star formation, formed at same time as Sun
"Tidal" Theory for Origin of Solar System
"Nebular Theory": Planets are ByProduct of Normal Star Formation
Implications of Formation Theories
"Tidal" Theory: planets RARE "Nebular" Theory: planets COMMON
Planets around Stars
Difficult to detect Until 1995, none known As of early 2008, >240 planets around nearby stars
Around Sun-like stars As many as 5 around a single star
Planetary systems are very common!
Proto-Planets around Stars
Many systems known where planets appear to be forming along with stars Nebular theory appears to be correct
Star Formation
Interstellar gas and dust
Interstellar Gas and Dust
Interstellar Gas and Dust
Dust Grain
Star Formation
Interstellar gas and dust
Concentrated into interstellar clouds Smaller ones are ~100,000 AU ~ 1 ly in diameter
Interstellar Cloud
Star Formation
Interstellar gas and dust
Concentrated into interstellar clouds Smaller ones are ~100,000 AU ~ 1 ly in diameter
Stars form in interstellar clouds
Eagle nebula
Eagle nebula
Eagle nebula
Eagle nebula
Eagle nebula
Orion Interstellar Cloud
Orion Interstellar Cloud
Visible Light
Visible Light
Infrared Light (0.1 mm)
Radio (CO at 2.6 mm)
Ground Based Image
HST Image
Star Formation
Interstellar gas and dust
Concentrated into interstellar clouds Smaller ones are ~100,000 AU ~ 1 ly in diameter
Stars form in interstellar clouds Gravity causes clouds to collapse to form rotating disks, star forms at center
Protostars in Orion
Evidence for disks in star forming regions
Beta Pictoris "Debris" Disk (Infrared)
Nebular Theory for Solar System
Solar Nebula = interstellar cloud of gas and dust, ~100,000 AU Gravity causes it to collapse
Nebular Theory for Solar System
Solar Nebula = interstellar cloud of gas and dust, ~100,000 AU Gravity causes it to collapse Conservation of angular momentum spins faster as collapses
Demonstrations of Angular Momentum
Nebular Theory for Solar System
Solar Nebula = interstellar cloud of gas and dust, ~100,000 AU Gravity causes it to collapse Conservation of angular momentum spins faster as collapses
Nebular Theory for Solar System
Solar Nebula = interstellar cloud of gas and dust, ~100,000 AU Gravity causes it to collapse Conservation of angular momentum spins faster as collapses Centrifugal force increase, nebula becomes more oblate, eventually forms a rotation disk
Solar Nebula Hypothesis
Solar system forms from a rotating cloud of interstellar gas Gravity collapse; causes rotation speed increases; disk forms Sun at center; planets form from dust and gas of disk
Disks They're Everywhere You Look
Same mechanism explains
Spiral galaxies Accretion disks around black holes Planetary rings (e.g., Saturn's rings)
Rotating Disk Explains:
If planets form out of rotating disk with rotating Sun at center, explains:
Plane of orbits Circularity of orbits Same direction of orbits Plane = equator of Sun Same direction of Sun's rotation Most planets rotate same direction as revolve
Rotating Disk Explains:
If planets form out of rotating disk with rotating Sun at center, explains:
Plane of orbits Circularity of orbits Same direction of orbits Plane = equator of Sun Same direction of Sun's rotation Most planets rotate same direction as revolve
Problem: Why doesn't Sun rotate very rapidly?
ProtoSun and Solar Nebula
Inside the Solar Nebula
Planetesimals
Small particles collide and stick together building up planetesimals Asteroids and comets are remnant planetesimals
Condensation vs. Distance
Temperature in disk decreases with distance from Sun
Condensation vs. Distance
Temperature in disk decreases with distance from Sun Temperature determines materials which free out (condense) from gas
1000 2000 K = metals 500 1000 K = rocks (& metals) 100 500 K = water ice (& metal, rock) 20 100 K = methane, ammonia ice (& metal, rock, water ice)
"Frost line" where water ice forms critical
Formation of Giant Planets
Ices more common than rock or metal Jovian planets start with massive icy/rock cores
Jovians attract and retain hydrogen and helium, the most abundance materials Jovians become giant planets
Higher mass higher escape velocity Cooler temperature atoms move slower
Neptune, Uranus have "slushy" cores leftover from formation
Outer Solar System Ice Worlds
Ices more common than rock or metal Smaller objects are ice worlds
Kuiper Belt Oort Cloud Comets Jovian moons
Interior Melting & Differentiation
Collisions Release Interior Materials
Types of Meteorites, Asteroids
Cleaning up the Construction Zone
Moon, Mercury, others heavily cratered Most cratering early in solar system history, ~4 bil...