1. Kirkwood Observatory Open House
Out-of-class Activity:
Every clear Wednesday evening for the rest of the semester.
Check website for details.

2. Homework #7
due Monday, March 29, 2:30 pm

3. Review session Monday, March 29
Exam #2
Wednesday, March 31
Review session Monday, March 29
7:30 –9:30 pm
Morrison Hall 007

4. Two “flavors” of planets
Terrestrial
Jovian  
Two “flavors” of planets

5. Terrestrial Planets Jovian Planets Size: small large
Location: closer to Sun distant
Composition: rocky/metallic gaseous/icy
Temperature: hotter cold
Rings: none ubiquitous
Rotation rate: slow rapid
Surface: solid not solid
Atmosphere: minimal substantial
Moons: few to none many

6. Planetary orbits:
1) Prograde
2) approximately coplanar
3) approximately circular
Rotation:
1) Mostly Prograde
2) Includes sun
3) Includes large moons

7. Surface features of solid objects in solar system

8. Craters are ubiquitous

9. There are lots of smaller objects in the Solar System, some are rocky and some are icy

10. Asteroids small Rocky Odd-shapes nearly circular orbits
orbit planes are near Ecliptic Plane
orbits in inner part of solar system

11. The
“asteroid belt”

12. Asteroids

13. Mars’ moons and the asteroid Gaspra
Deimos
Phobos

14. Comets small nucleus very large tails “dirty snow ball”
highly eccentric orbits
all orbit inclinations

15. Comet Wild
Halley’s Comet

17. Comets are found mainly in two regions of the solar system

20. Kuiper Belt Objects
UB313
(1500 miles)

21. So how do we account for what we see in the solar system?

22. The Nebular Theory
The Solar system was formed from a giant, swirling interstellar cloud of gas and dust (the solar nebula)

23. The Solar nebula may have been part of a much larger nebula

24. Protostellar nebulae?

25. Recipe for solar system formation
Start with a giant, swirling interstellar cloud of gas and dust (nebula)

26. Recipe for solar system formation
Start with a giant, swirling interstellar cloud of gas and dust (nebula)
Perturb cloud to begin its collapse
Sit back and let physics take over

27. Important physics in forming stars
stars & planets
Gravity
Gas pressure
Conservation of Angular Momentum
Conservation of Energy
Phases of matter

28. stellar/planetary systems
The struggle to form
stellar/planetary systems
Gravity vs Gas Pressure

29. Protosolar nebula System initially in pressure balance – no collapse
Slowly rotating
System initially in pressure balance – no collapse

30. Gravity seeks to collapse cloud
System initially in pressure balance – no collapse

31. Gas pressure seeks to expand cloud
System initially in pressure balance – no collapse

32. System initially in balance – no collapse
gas pressure
gravity
System initially in balance – no collapse

33. gas pressure
gravity
Now, whack the cloud

34. Perturbation triggers collapse – gravity is winning
As collapse proceeds, rotation rate increases

35. As collapse continues, the rotation rate
increases while nebula flattens

36. Most of this was in gaseous form!
Building the Planets. I
COLLAPSE OF PROTOSTELLAR CLOUD INTO A ROTATING DISK
Composition of disk:
98% hydrogen and helium
2% heavier elements (carbon, nitrogen, oxygen, silicon, iron, etc.).
Most of this was in gaseous form!

37. Collapse of the Solar Nebula
As the solar nebula collapsed to a diameter of
200 A.U. (1 LY = 63, 240 AU), the following happened:
The temperature increased as it collapsed (conservation of energy; gravitational potential energy becomes thermal energy)
The rotation rate increased (conservation of angular momentum)
The nebula flattened into a disk (protoplanetary disk)
Motions of material in the disk became circularized

38. Material in the newly formed proto-planetary disk is:
Orbiting in approximately the same plane
Orbiting in approximately circular orbits
This is the situation with the orbits of planets, so now we have the material in the proper location and moving in the proper manner.

39. Examples of proto-planetary disks

40. Building the Planets. II
There was a range of temperatures in the proto-solar disk, decreasing outwards
Condensation: the formation of solid or liquid particles from a cloud of gas (from gas to solid or liquid phase)
Different kinds of planets and satellites were formed out of different condensates

41. Ingredients of the Solar Nebula
Metals : Condense into solid form at 1000 – 1600 K
iron, nickel, aluminum, etc. ; 0.2% of the solar nebula’s mass
Rocks : Condense at 500 – 1300 K
primarily silicon-based minerals; 0.4% of the mass
Hydrogen compounds : condense into ices below ~ 150 K water (H2O), methane (CH4), ammonia (NH3), along with carbon dioxide (CO2), 1.4% of the mass
Light gases (H & He): Never condense in solar nebula
hydrogen and helium.; 98% of the mass

42. The "Frost Line” - Situated near Jupiter
Rock & Metals can form anywhere it is cooler than about 1300 K.
Carbon grains & ices can only form where the gas is cooler than 300 K.
Inner Solar System: Too hot for ices & carbon grains.
Outer Solar System: Carbon grains & ice grains form beyond the "frost line".

44. Building the Planets. III Accretion
Accretion is growing by colliding and sticking
The growing objects formed by accretion – planetesimals (“pieces of planets”)
Small planetesimals came in a variety of shapes, reflected in many small asteroids
Large planetesimals (>100 km across) became spherical due to the force of gravity

45. In the inner solar system (interior to the frost line), planetesimals grew by accretion into the Terrestrial planets.
In the outer solar system (exterior to the frost line), accretion was not the final mechanism for planet building – nebular capture followed once accretion of planetesimals built a sufficiently massive protoplanet.

46. Building the Planets. IV. Nebular Capture
Nebular capture – growth of icy planetesimals by capturing larger amounts of hydrogen and helium. Led to the formation of the Jovian planets
Numerous moons were formed by the same processes that formed the proto-planetary disk
Condensation and accretion created “mini-solar systems” around each Jovian planet

47. Building the Planets. V. Expulsion of remaining gas

48. The Solar wind is a flow of charged particles ejected by the Sun in all directions. It was stronger when the Sun was young. The wind swept out a lot of the remaining gas

49. Building the Planets. VI. Period of Massive Bombardment

50. Planetesimals remaining after the clearing of the solar nebula became comets and asteroids
Rocky leftovers became asteroids
Icy leftovers became comets
Many of them impacted on objects within the solar system during first few 100 million years (period of massive bombardment - creation of ubiquitous craters).

51. Brief
Summary