1. Chapter 19: Origin of the Solar System

2. Any GOOD hypothesis about the origin of the solar system must explain most - if not all - of its characteristics:
All of the planets orbit the sun in the same direction, and in the same plane
The planets closest to the sun are small and rocky, have few moons
The planets further from the sun are large and contain more gas and icy materials
Most of the Moons orbit their planets in the same direction as the planets orbit the sun
Oldest meteorites are about billion years old
Planetary surfaces are all younger than the oldest meteorites

3. Relative sizes of the planets

4. Sun-planet distance (relative to Earth: AU)
Mercury 0.4 AU
Venus 0.7
Earth 1.0
Mars 1.5
Jupiter 5.2
Saturn 9.5
Uranus 19
Neptune 30
Sun = 1 mm on this scale, of 1 m = 1 AU
1 AU = 150 million km

5. Other residents of the solar system:
1. Dwarf planets
diameter = km, smaller than Moon, orbit the sun

6. Other residents of the solar system
2. Asteroids - rocky, d < 1000 km, orbit the sun

7. Other residents of the solar system
3. Comets - rock & ice, wide range of sizes (~10 m to 100 km)

8. Other residents of the solar system
4. Moons - orbit planets, some are larger than Mercury

9. Other residents of the solar system
5. Meteoroids - small fragments of asteroids that enter earth’s atmosphere (dust to boulder sized)

10. How many of the planets orbit the Sun in the same direction?
About half
All except 1 or 2
All of them, no exceptions

11. What fraction of moons orbit their planet in the same direction as the orbit around the Sun?
None
About half
Most - a few exceptions
All of them, no exceptions

12. Any GOOD hypothesis about the origin of the solar system must explain most - if not all - of its characteristics:
All of the planets orbit the sun in the same direction, and in the same plane
The planets closest to the sun are small and rocky, have few moons
The planets further from the sun are large and contain more gas and icy materials
Most of the Moons orbit their planets in the same direction as the planets orbit the sun
Oldest meteorites are about billion years old
Planetary surfaces are all younger than the oldest meteorites

13. Interstellar cloud of gas & dust collapsed under its own gravity
Predicted that protoplanetary nebulae would be observed
Explains all of the major features of solar system, and also the exceptions
Observations continue to support this theory

15. Protoplanetary disks last for only about 1-10 million years

16. What are the planets made of?
Element how many atoms gas or solid at
(total) Earth Jupiter
________________________________________________
Hydrogen 705,700 gas gas
Helium 275,200 gas gas
Carbon 3,032 gas soot (solid)
Nitrogen 1,105 gas ice
Oxygen 5,920 H2O gas H2O ice
Silicon rock rock Iron 1,169 metal metal

17. Planet formation: Terrerstrial vs. giant planets
Giant (“jovian”)
Lots of solids in the disk (cold > 5 AU)
Cores form from ice, rock and metal
Grow large, quickly (~1 million years)
Big enough to trap H and He gas from disk
Terrestrial (“earth like”)
Very little solid material in disk at 1 AU
Form from rock and metal only
Grow slowly (~100 million years)
Too small to trap any gas from disk

18. The next billion years: Debris disks
Gas and fine dust blows away after ~ 10 million years
Older stars have ‘debris disks’ around them
Need a supply of larger objects to regenerate the dust that gets blown away
evidence of planets forming around other stars
Debris disks are analogous to the Oort cloud and Kuiper belt of comets, and the asteroid belt

19. Asteroid belt

21. The Nebular theory predicts most other sun-like stars should have planets
Do they?

22. 358 planets have been found around other stars!!!

23. Detecting planets around other stars: Doppler method

24. Transit method (Kepler Mission)