Solar Nebula Theory. Basic properties of the Solar System that need to be explained:

Transcription

1 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

2 Star Formation Interstellar Medium (ISM): Gas & dust between stars ( atoms/cm 3 ) Composition Gas: 70% H (neutral H, H +, H 2 ) 22 25% He 3 5% metals Dust: Silicate grains (rock/sand) Graphite (Carbon) Basic organic material

3 Nebula (Large cloud of ISM) Star Formation - low density (200 atoms/cm 3 ) - D ~ 150 L.Y. - T ~ 20 K - M ~ M Suns

4 Gravity causes: - globule to contract - material to accumulate - central region to heat up Globule Characteristics: - D ~ L.Y. - M ~ M Sun - Density ~ atoms/cm 3 - T ~ K

5 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 T core ~ 15 million K, H! He fusion reactions start in core

6

7 Solar Nebula Theory Nebula material is uniformly spread through the proto-planetary disk Condensation Sequence: different materials condense at different temperatures

8 Solar Nebula Theory Ice line: found between Mars and Jupiter Inner disk: metals/silicates (Terrestrial Planets) Outer disk: ices and gases (Jovian Planets)

9 Proto-Sun & Proto-planetary Disk

10 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)

11 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

12 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 Double Planet Theory Pros overall composition Cons avg. density < Earth s Fission Theory Capture Theory low avg. density explains orbital plane how? orbit not above equator densities too similar third body?

13 Large Impact Theory Formation of the Moon 1) Mars sized object struck Earth early on in its history. 2) Crust material is vaporized ) Material concentrates along the ecliptic. 4) Moon forms. Best explains all the qualities of the Moon.

14 Extra-Solar Planets 1 st 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

15 First Confirmed Photograph of Exoplanet

16 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

17 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.

18 Star-Planet Systems 7.80 x 10 8 km For the Sun-Jupiter system, the COM is 7.39 x 10 5 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

19 Extra-Solar Planet System Methods of Observation Spectrum of host star will periodically shift as v r changes

20 Methods of Observation Some stars have multiple planet systems Upsilon Andromedae

21 HD st ES Planet detected by watching the planet transit host star Spectral analysis has shown evidence of Sodium in planet s atmos.

22 ES Planet Properties Characteristic Mass Semi-major axis P orb Eccentricity Range M Jupiter AU days 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