formation of the solar system - sites.uni.edu · 3/3/2013 3 formation mechanism inward pull of...
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Formation of the Solar System H – 78%
He – 20%
O – 0.8%
C – 0.3%
N – 0.2%
Ne – 0.2%
Ni – 0.2%
Si – 0.06%
Fe – 0.04%
S – 0.04%
Etc.
Origins?
ISM – Interstellar Medium
Mainly in gas form
Molecules
~150 different molecules found
H2, CO, O2, H2O most common
NH3, CH4, HCN, CH3OH, H2CO, C2H5OH, NaCl
Form in gas, on surface of dust grains
Dust – 1% of ISM
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2 Atoms – AlCl, AlF, AlO, C2, CH, CH + , CN, CN + , CN -, CO, CO + , CF + , CP, CS, FeO, H2,
HF, HCl, KCl, NaCl, NH, N2, NO, NO + , NS, NaI, O2, OH + , HO, PN, PO, SO, SO + , SiC, SH,
SH + , SiN, SiO, SiS, MgH+
3 Atoms – AlNC, AlOH, C3, C2H, C2O, C2S, C2P, CO2, CO2+, H3
+, H2C, H2Cl+, HCO, HCO+,
HCP, HCS+, HOC+, H2O, H2O+, H2S, H2S
+, HCN, HNC, HNO, KCN, MgCN, MgNC, HN2+,
N2O, N2H+, NaCN, OCS, O3, SO2, c-SiC2, NH2, SiCN, SiNC
4 Atoms – CH3, c-C3H, l-C3H, C3N, C3N-, C3O, C3S, C2H2, HCCN, HCNO, HOCN, HCNH+,
HNCO, HNCS, HOCO+ , H2CO, H2CN, H2CN+ , H2CS, H3O+, HSCN, NH3, SiC3
5 Atoms - C5 C4H, C4H-, SiC4, l-H2C3, c-C3H2, CH4, HC3N, HCOOH, H2CNH, H2C2O, H2CCN,
SiH4 H2COH+, HCC-NC, NH2CN, HC(O)CN
6 Atoms - C5H, C2H4, CH3CN, CH3NC, CH3OH, CH3SH, HC3NH+, HC2CHO, HCONH2, l-
H2C4, c-H2C3O, C5N, HC4N, CH2CNH
7 Atoms - C6H, C6H-, CH2CHCN, CH3C2H, c-C2H4O, H3CNH2, H2CHCOH, HC4CN, CH3CHO
8 Atoms – H3CC2CN, H2COHCHO, HCOOCH3 CH3COOH C7H H2C6 CH2CHCHO,
CH2CCHCN, NH2CH2CN
9 Atoms - CH3C4H, CH3OCH3, CH3CH2CN, CH3CONH2, CH3CH2OH, HC7N, C8H, C8H-,
CH3CHCH2
10 Atoms - CH3C5N, (CH3)2CO, (CH2OH)2, CH3CH2CHO 11 Atoms – HC8CN, C2H5OCHO, CH3C6H, HCOC2H5
12 Atoms – C3H7CN, C6H6
13 Atoms - HC11N, HC10CN
24 Atoms – C14H10
60 Atoms – C60
70 Atoms – C70
Sources of ISM
AGB stars
Dust formation
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Formation Mechanism
Inward pull of gravity vs. gas pressure
• Jean’s Mass
MJeans=mass
, G =constants
m=mean molecular weight
1
T=Temperature
r=average density
rm
1
4
32/12/3
G
TMM Jeans
• Collapse happens quickly/slowly?
• Freefall time
Higher density – quicker collapse
Rotation rate, collapse rate multiple stars?
2/1
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3
r
Gt ff
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• Theoretical collapse of cloud
– Energy lost (if transparent)
– Density increase (opacity increases)
– Temperature increase
– Deuterium fusion (1 million K)
• Slow down
– Further contraction
– Heating of proto-star heats cloud
• Long IR at first
• Short IR later
• Reality?
Bok Globules
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• Star formation buried in Cocoon Nebula
– Cloud of gas/dust (100:1)
– Few 100 AU in size
– Strong IR source
• Observations
– R Mon & other IR stars
– Proplyds (proto-planetary disks)
• Observed in Orion nebula, Carina nebulae, etc.
• <1 million years old
R Mon T Tauri
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H-H Objects
• Outflows of material
• Observed near Bok globules
• 400 exist
• ½ pc from source star
• 100 – 1000 km/s
later on…
• Collapse of cloud material – In disk around proto-star
– Eventually becomes transparent (after formation of larger particles)
• Star formation finishes up during T Tauri stage – Bright (large radius)
– Fast rotation
– Found near nebulae
– IR excess
– Strong magnetic fields*, large sun/star spots
– Lasts ~100 million years (limits planet formation)
– Excess of Li - young
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What about forming planets?
Look at the disks
Several hundred AU in size Kuiper belt
Composition Comet
Gap in inner part (cleaned out)
Mass ~ 0.001 – 0.1 M
Some ring-like
Beta Pictoris – 1500 AU wide
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• Disk Material
– Distribution depends on angular momentum
– Infall heats disk up
1500 K near 1 AU
100 K near 10 AU
– Temperature gradient Energy transport
• Convection ( to disk)
• Turbulence (radially)
• Composition distribution (limited)
• Now you’re ready to make a planet! Or two.
Planet Formation
• When did it happen?
– When the planets formed?
– When the material formed?
• Radiometric dating (isotope )
– Many short lived radioactive elements
• 41Ca (0.15 Myr), 26Al (1.1 Myr), 60Fe (2.2 Myr), 53Mn (5.3 Myr), 107Pd (9.4 Myr), 182Hf (13 Myr), 129I (23 Myr), etc.
• Source? – Large star (Supernova, Evolved supergiant)
– Spallation
• Chemical distribution – how’d that happen?
– Example: Oxygen
• Gas: O2, CO, CO2, H2O, etc.
• Liquid/solid: H2O, CO2, etc.
• Solids: Silicates, ferrous oxide, olivine, serpentine, etc.
• Definitions: Minerals & Rocks
– Mineral – what’s that?
• Examples?
– Rock – what’s that?
• Examples?
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Minerals
• Several different groups –
– Silicates (Si, O)
• On Earth ~95% are silicates
• Common silicates – Silica: Quartz
– Feldspars: Orthoclase feldspars, Plagioclase feldspars
– Pyroxenes
– Amphiboles
– Micas
– Olivines (tend to sink)
Non-silicates
Such as
– Oxides
• Usually Fe+O:
Magnetite, hematite, limonite (Mars)
Ilmenite, Armalcolite (Moon’s maria)
– Pyrite (FeS2), Troilite (FeS) – in cores
– Clay minerals – hydrous aluminum silicates
Outer solar system
– Carbonaceous minerals: graphite, carbon rich
– Ices: Water, CO2, NH3, CH4
Rocks
• Three types
– Igneous
• Lavas
• Basaltic
• Grantitic
• Andesite
• Anorthosite
• Obsidian
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• Sedimentary – atmosphere/hydrosphere/crust
– Weathering of rocks
• Chemical
• Mechanical
– Transport
– Layering, settling
Types:
• Shale
• Sandstone
• Limestone
• Dolomite
• Evaporites (halite, gypsum)
• Metamorphic
– Altering, re-crystallization
• Pressure
• Temperature
• Chemistry
– Examples:
• Marble
• Quartzite
• Gneiss
• Schist
• Slate
• Shocked quartz
• Metamorphic
– Altering, re-crystallization
• Pressure
• Temperature
• Chemistry
– Examples:
• Marble
• Quartzite
• Gneiss
• Schist
• Slate
• Shocked quartz
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• Mineral evolution – depends on location
– Temperature
– Pressure
– Interactions available (other elements/minerals)
• Ex: formation of CO depletes not only C, but also O
• Remember the starting situation:
– H, He, O, C, N, etc.
– H, He not common in planets (in terms of ratio)
– Other abnormalities need to be explained
• T>2000 K – Everything evaporated, no formation
• T ~ 1700 K – REE, oxides of Al, Ca, Ti form
• Corundum (Al2O3)
• Perovskite (CaTiO3)
• Spinel (MgAl2O4)
• T ~ 1400 K – Iron – Nickel alloy forms
• T < 1400 K – Magnesium silicates form
• Forsterite (Mg2 SiO4)
• Enstatite (MgSiO33)
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• T < 1200 K
– Feldspars start to appear
– First are plagioclase anorthite (CaAl2Si2O8)
– Later (T~ 1000 K) sodium and potassium feldspars ((Na, K)AlSi3O8)
• T ~ 700 K
– Iron, H2S react, form troilite (FeS)
• T ~ 500
– Iron, water react, form iron oxide
(Fe+H2O FeO+H2)
Iron oxide reacts with enstatite, forsterite form olivines ((Mg, Fe)2SiO4), pyroxenes ((Mg,Fe)SiO3)
• T < 500 K
– Water major player (gas)
– Reacts with olivines, pyroxenes to form hydrated silicates
• Serpentine Mg6Si4O10(OH)8
• Talc Mg3Si4O10(OH)2
• Tremolite Ca2Mg5Si8O22(OH)2
• Hydroxides like Brucite Mg(OH)2
• T < 200 K
– Water ice forms (mineral)
– Cooler temperatures
• Ammonia, methane condense as hydrates, clathrates
• Below 60 K
– CO, N2 form clathrates with H2O ice
• Below 40 K
– CH4, Ar ices form
• Below 25 K
– CO, N2 form ices
Exceptions – find high temperature minerals inside of low temperature structures (carbon rich meteorites). Requires migration.
Temperature structure changes over time
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Let’s make some planets
• Minerals formed – what’s next?
• Particles must come together safely
– Why?
– How?
• Corpuscular dragging
• Electrostatic forces
• Gravitational perturbations
• Safe when they are planetismals
– 0.001 m – 1000’s of meters
– Grow via collisions
Growth depends on
– Density
– Relative velocities
At 1 AU, and Earth forms in 107 – 108 years
(most growth early on)
Further out, density lower, growth rates slower.
At 5 AU, takes 108 years to form Jupiter
Uh-oh!
Too late!
T Tauri will destroy it!
Need to speed up growth rates.
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Runaway growth mechanism
Requires relative velocities < escape velocities
Limits region of growth
Can extend beyond Hill sphere
Perturbations, gas drag also help
Terrestrial Formation • Heating up
– Collisions, Radioactive decay, Gravitational, Chemical processes
• Energy lost
• Energy transport – Convection vs Conduction
• Primitive Atmosphere – H2O CO2
• Surface melting (M ~ 0.2 M, T~1600 K)
• Atmosphere evolution
– Loss of light-weight gases
– Impacts, outgassing
Gas Giant Formation
• Quick formation (~107 years)
• Core formation first (similar to terrestrial)
• M ~ 10-20 M, gas infall significant
• Eventually reach runaway accretion
• Fills Hill sphere (100’s x current size)
• Contraction (fast then slow) ~10,000 years
• Heating – convection
• Temperature, Luminosity (IR) stabilize
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Ice Giant Formation
• Similar to gas giant (but more heavy elements)
• Cores less massive (less material)
• No runaway
• Contraction ends after 200,000 years
Loose Ends
• Asteroid belt
– Not a planet (too little mass)
– Formerly more objects there
– Jupiter’s influence
– Formed in current location
• Cometary masses
– Formed between 3-30 AU
– Ejected by Gas/Ice giants (mainly Jupiter)
– Migration of Jupiter inwards, other giants outward
• Satellites
– Similar to solar system formation scenario
– Regular (Normal) satellites:
• Found near equatorial plane of planet
• Prograde orbit, rotations, low eccentricity, inclination
• Formed with planet
– Irregular (Captured) satellites:
• Random orientations, orbits, motions, retrograde
• Formed elsewhere – ice/rock, ice composition
– Collision satellites:
• Earth-Moon, Pluto system, Asteroids
• “Chip off the old block”
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• Rings
– Not primordial
– Short lived structures
– Composition peculiarities
– Fed by external sources, local sources
HD 100546
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