An Artist’s Impression

The young Sun gas/dustnebula

solid planetesimals

Sequence of events• 1. Nebular disk

formation• 2. Initial coagulation

(~10km, ~104 yrs)• 3. Runaway growth (to

Moon size, ~105 yrs)• 4. Orderly growth (to

Mars size, ~106 yrs), gas loss (?)

• 5. Late-stage collisions (~107-8 yrs)

Timescale Summary

Runaway growth

Orderly growth

Late-stage accretion(Giant impacts. Gas loss?)

Dust grains

~Moon-size(planetesimal)

~Mars-size(embryo)

~Earth-size(planet)

~1 Myr

~0.1 Myr

~10-100 Myr

What does our Solar System consist of?• The Sun 99.85% of the mass (78% H, 20%

He)• Nine Eight Planets• Satellites (Moons)• Comets, asteroids, Kuiper Belt Objects, etc.

Where is everything?

J S U N P

1 AU is the mean Sun-Earth distance = 150 million kmNearest star (Proxima Centauri) is 4.2 LY=265,000 AU

KB

Me V E Ma

Note log scales!

Inner solar system

5 AU1.5 AU

Outer solar system

30 AU

Note logarithmic scales!Me V MaE

Gas giants Ice giants Terrestrial planets

Basic dataDistance (AU)

Porbital (yrs)

Protation

(days)

Mass (1024kg)

Radius (km)

r(g cm-3)

Sun - - 24.7 2x106 695950 1.41

Mercury 0.38 0.24 58.6 0.33 2437 5.43

Venus 0.72 0.62 243.0R 4.87 6052 5.24

Earth 1.00 1.00 1.00 5.97 6371 5.52

Mars 1.52 1.88 1.03 0.64 3390 3.93

Jupiter 5.20 11.86 0.41 1899 71492 1.33

Saturn 9.57 29.60 0.44 568 60268 0.68

Uranus 19.19 84.06 0.72R 86.6 24973 1.32

Neptune 30.07 165.9 0.67 102.4 24764 1.64

Pluto 39.54 248.6 6.39R 0.013 1152 2.05

See e.g. Lodders and Fegley, Planetary Scientist’s Companion

Nebular Composition• Based on solar photosphere and chondrite compositions,

we can come up with a best-guess at the nebular composition (here relative to 106 Si atoms):

Data from Lodders and Fegley, Planetary Scientist’s Companion, CUP, 1998This is for all elements with relative abundances > 105 atoms.

Element H He C N O Ne Mg Si S Ar Fe

Log10 (No. Atoms)

10.44 9.44 7.00 6.42 7.32 6.52 6.0 6.0 5.65 5.05 5.95

Condens.Temp (K)

180 -- 78 120 -- -- 1340

1529 674 40 1337

• Blue are volatile, red are refractory• Most important refractory elements are Mg, Si, Fe, S

(makes up the rocky planets)

Terrestrial (silicate) planets

• Consist mainly of silicates ((Fe,Mg)SiO4) and iron (plus FeS)

• Mercury is iron-rich, perhaps because it lost its mantle during a giant impact (more on this later)

• Volatile elements (H2O,CO2 etc.) uncommon in the inner solar system because of the initially hot nebular conditions

• Some volatiles may have been supplied later by comets• Satellites like Ganymede have similar structures but have an ice

layer on top (volatiles are more common in the outer nebula)

Mercury

Venus Earth

Moon

Mars

Ganymede

Io

F.Nimmo EART164 Spring 11

Venus Earth Mars Titan Jupiter Saturn Uranus Neptune

Solar constant (Wm-2) 2620 1380 594 15.6 50.5 14.9 3.7 1.5

Obliquity (o) 177 23.4 24.0 (27) 3.1 26.7 98 28.3

Orbital period (years) 0.62 1 1.88 (29.4) 11.9 29.4 84 165

Rotation period (hours) 5832 24 24.6 383 9.9 10.7 17.2 16.1

Bond albedo A 0.76 0.4 0.15 0.3 0.34 0.34 0.3 0.29

Molecular wt. m (g/mol)

43 29 43 29 2.2 2.1 2.6 2.6

Tsurface or T1bar (K) 730 288 220 95 165 134 76 72

Surface pressure (bar) 92 1 .007 1.47 n/a n/a n/a n/a

g (ms-2) 8.9 9.8 3.7 1.35 24.2 10.0 8.8 11.1

Teq (K) 229 245 217 83 113 84 60 48

Scale height H (km) 15 8.5 12 23 27 60 28 20

Radius (km) 6052 6370 3390 2575 71,500 60,300 25,000 24,800

Mass (1024 kg) 4.87 5.97 0.64 0.13 1900 568 87 102

Useful Data

Data mostly from Taylor, Appendix A