1. Making Solar Systems and Planets
present-day solar system
-- kinds of planets
newly-forming stars
-- conditions during planet formation
planets around other stars
-- mass, radius, density for other planets
EVIDENCE:

2. Characteristics of the Solar System
1) ORBITS
Planets orbit in almost same plane (Pluto and Eris don’t) and in same direction as Sun spins
Planet orbits are nearly circular (except Pluto, Eris, and Mercury)
flipping a coin to determine if planet is going to go one way or another…

3. Thought Question:
If you flipped a coin to decide which direction each of the 8 planets went around the Sun, what is the probability that all of them would end up going around in the same direction?
More than 99%
About 75% (only a 1 in 4 chance they wouldn’t)
About 50%
About 25% (only a 1 in 4 chance they would)
Less than 1%
Answer: 5. (%)

4. Characteristics of the Solar System
VIEWS FROM ABOVE NORTH POLE:
SUN
2) ROTATION
Planets rotate in same counterclockwise direction as orbit (except Venus and Uranus)
Moons orbit planet in same direction (with 2 exceptions) and near planet equator

5. THERE IS A SPECIAL DIRECTION IN THE SOLAR SYSTEM
Mention spin axes of Venus and Uranus?

6. Characteristics of the Solar System
3) MASSES
99.9% of solar system mass is in Sun
Most of rest is in Jupiter
Sun and planets to scale:

7. FEW MASSIVE OBJECTS, MANY LOW-MASS OBJECTS
MORE RAW MATERIALS FOR SOME?

8. Characteristics of the Solar System
DISTANCE FROM SUN:
4) TYPES OF PLANETS
Terrestrial planets:
close to Sun (a < 1.5 AU)
small, dense, mostly metals and rock

9. Characteristics of the Solar System
EARTH
(for comparison)
Scale questions
Jovian planets:
Far from Sun (a > 5 AU)
4-11x Earth size, x Earth mass
low density, mostly hydrogen and helium

10. Average Density
HOLLOW PLANET ROCKY PLANET METALLIC PLANET
LESS DENSE MORE DENSE
Coke versus Diet Coke; thought question?
density reveals something about mixture of materials in planet

11. Average Density Common Materials (units of g/cm3):
Air: 0.001
Water: Jovian Planets: 1-2
Rock: Terrestrial Planets: 4-5
Iron: 8
Lead: 11
Gold: 19
Coke versus Diet Coke; thought question?
Jovian planets are mixtures of light materials (hydrogen, helium, and “ices”)

12. Ceres (dwarf planet) in color
About 1/3rd of asteroid belt’s entire mass!
Ceres: M = 9.4x10^20 kg Moon: 7.35x10^22 kg (78x Ceres)
Diameter = 950 km R = 1738 km (3.6x Ceres, 50x volume)
Density: 2.1 g/cm^ g/cm^3

13. Characteristics of the Solar System
5) LEFTOVERS
Asteroids mostly orbit between Mars and Jupiter
Comets usually come from far outside Neptune’s orbit
something about all of the detected objects so far?

15. Characteristics of the Solar System
asteroid Eros (computer reconstruction)
nucleus of comet Halley
5) LEFTOVERS: small bodies less than 1000 km across
Asteroids: rocky bodies
Comets: icy/rocky bodies
-- “ice” includes water (H2O), ammonia (NH3), methane (CH4)

16. Characteristics of the Solar System
Scale questions
Ice dwarf planets:
VERY far from Sun
small, low density (1-2 g cm-3), ice/rock

18. Ice Dwarfs
orbits more elliptical than Pluto’s (which is more elliptical than planet orbits)
thrown out by gravity of giant planets?
SEDNA
ERIS
PLUTO

19. “SIDE VIEW” OF SOLAR SYSTEM
Ice Dwarfs
ERIS
SEDNA
“SIDE VIEW” OF SOLAR SYSTEM
inclination: angle between planet orbit and Earth orbit
ice dwarf orbits are more inclined than Pluto’s (which is more inclined than planet orbits)