Download Solar Nebula Theory

Solar Nebula Theory
Basic properties of the Solar System that need to be explained:
1. All planets orbit the Sun in the same direction as the Sun’s rotation
2. All planetary orbits are confined to the same general plane
3. Terrestrial planets form near the Sun, Jovian planets further out
Other aspects include:
- similar direction of rotation
- ring systems
- asteroid/Kuiper belt
- formation of natural satellites
- angular momentum problem
Star Formation
Interstellar Medium (ISM): Gas & dust between stars
(100 – 200 atoms/cm3)
Composition
Gas: 70% H (neutral H, H+, H2)
22 – 25% He
3 – 5% “metals”
Dust: Silicate grains (rock/sand)
Graphite (Carbon)
Basic organic material
Star Formation
Nebula (Large cloud of ISM)
- low density (200 atoms/cm3)
- T ~ 20 K
- D ~ 150 L.Y.
- M ~ 104 – 106 MSuns
Globule Characteristics:
- D ~ 0.1 – 5 L.Y.
- M ~ 1 – 1000 MSun
- Density ~ 107 – 109 atoms/cm3
- T ~ 100 – 200 K
Gravity causes:
- globule to contract
- material to accumulate
- central region to heat up
Star Formation
Rotation causes:
- Densest region to become spherical (proto-star)
- Outer gases cast off into proto-planetary disk
1. Cool protostar collapses under gravity
2. Pressure inside builds up which increases temperature
3. Protostar shrinks & heats up more
4. Once Tcore ~ 15 million K, H ! He fusion reactions start in core
Solar Nebula Theory
Nebula material is uniformly spread through the proto-planetary disk
Condensation Sequence: different materials condense at different
temperatures
Solar Nebula Theory
Ice line: found between Mars and Jupiter
Inner disk: metals/silicates (Terrestrial Planets)
Outer disk: ices and gases (Jovian Planets)
Proto-Sun & Proto-planetary Disk
Solar Nebula Theory
Dust grains grow by accumulating atoms to form planetesimals
Planetesimals grow larger through collisions
Large planetesimals become spherical and act as congregating
sites (Proto-planets)
Planet Formation
Terrestrial
- Interior heating causes differentiation; leads to layered interior
- Primitive H, He atmospheres heated away
- Out-gassing creates present atmospheres
Jovian
- H, He gases and ices accrete quickly (grow large/massive)
- Natural satellites form
Formation of the Moon
Properties that need to be explained:
- Overall composition is similar to Earth.
- Moon’s density is similar to Earth’s crust
- Orbital plane is close to Ecliptic
- Lack of water on the Moon.
Formation Theory
Pros
Cons
Double Planet Theory
• overall composition • avg. density < Earth’s
Fission Theory
• low avg. density
• how?
• orbit not above equator
Capture Theory
• explains orbital
plane
• densities too similar
• third body?
Formation of the Moon
Large Impact Theory
1) Mars’ sized object struck Earth early on in its history.
2) Crust material is vaporized.
1
2
3
4
3) Material concentrates along the ecliptic.
4) Moon forms.
Best explains all the qualities of the Moon.
Extra-Solar Planets
1st discovered in 1995 around the star 51 Pegasi
144 as of April 2005
None have been seen directly:
- must look for indications of planet’s presence
First Confirmed Photograph of Exoplanet
Binary Systems
Two stars gravitationally bound after formation (~ 55% stars in MW)
Each star orbits the center of mass (COM) (“balance point”)
Stars of equal mass: COM equidistant from each star
Binary Systems
Stars of unequal mass: COM closer to more massive star
Massive star " small orbit; Low mass star " larger orbit
Use the orbital properties to estimate masses.
Star-Planet Systems
7.80 x 108 km
For the Sun-Jupiter system, the COM is 7.39 x 105 km from the
Sun’s center.
As Jupiter orbits the Sun, the Sun “wobbles” around the COM
A star’s spectrum will shift its appearance as the host star “wobbles”
Methods of Observation
Extra-Solar Planet System
• Spectrum of host star will periodically shift as vr changes
Methods of Observation
Some stars have multiple planet systems
Upsilon Andromedae
HD 209458
1st ES Planet detected by watching the planet transit host star
Spectral analysis has shown evidence of Sodium in planet’s atmos.
ES Planet Properties
Characteristic
Mass
Range
0.05 – 17 MJupiter
Semi-major axis
Porb
Eccentricity
0.04 – 5 AU
3.0 – 4080 days
0.0 – 0.93
• Very large & orbit very close to their host star
• Simulations predict terrestrial-type planets ejected from system
• Smaller planets will be detected as technology progresses