1. Ch. 4 – Formation of the Solar System and other Planetary Systems
Stars produce the heavier elements.
Formation of the Solar System (stardust, gravity, rotation, heat, and collisions).
Comparative Planetology (characteristics of the planets of the solar system).
Debris and remnants in the solar system.
Extrasolar planets (outside the solar system).

2. The heavy elements in the solar system were formed in an earlier generation of stars
The early Universe contained only hydrogen, helium, and traces of lithium.
All heavier elements were created in the core of stars as they “burned” the hydrogen and helium into carbon, oxygen, neon, calcium, magnesium, silicon, and iron
These were then expelled into space by
- stellar winds (happening with our sun now)
- planetary nebulae (not planets, but similar appearance to early astronomers) - see slides
- nova and supernova explosions

3. Solar Prominence – photo by SOHO spacecraft
from the
Astronomy
Picture of
the Day site
link

4. Helium Shell Burning on the Horizontal Branch

5. A G-Type Star is similar to our Sun
A G-Type Star is similar to our Sun. The evolution is shown during an imaginary trek through space. At the end of the red giant stage, the core is small, the envelope huge, and the outcome depends on the total mass of the star.

6. Planetary Nebulae form when the core can’t reach 600 million K, the minimum needed for carbon burning.

7. A Planetary Nebula shaped like a sphere, about 1. 5 pc across
A Planetary Nebula shaped like a sphere, about 1.5 pc across. The white dwarf is in the center.

8. A Planetary Nebula with the shape of a ring, 0
A Planetary Nebula with the shape of a ring, 0.5 pc across, called the “Ring Nebula”.

9. Cat’s Eye Nebula, 0.1 pc across, may be from a pair of binary stars that both shed envelopes.

10. M2-9 has twin lobes leaving the central star at 300 km/sec, reaching 0
M2-9 has twin lobes leaving the central star at 300 km/sec, reaching 0.5 pc end-to-end.

11. A Nova is an explosion on a white dwarf, but only a small amount of material on the surface of the white dwarf explodes. Nova Herculis a) in March b) in May 1935, after brightening by a factor of 60,000

12. Nova Persei - matter ejection seen 50 years after the 1901 flash (it brightened by a factor of 40,000)

13. Another dramatic result of stellar evolution: a supernova remnant which expels heavy elements into space.

14. The Solar System

15. Dark Dust Clouds: not just an absence of stars!

16. A Dark Cloud: dust and gas, dense enough to block starlight.

17. Radio Emission reveals the dark dust cloud.

18. Horsehead Nebula (The neck is about 0
Horsehead Nebula (The neck is about pc across) A nice example of a dark dust cloud

19. Formation of the Solar System
There are several kinds of objects in our Solar System
Terrestrial planets: Mercury, Venus, Earth, and Mars
Jovians: the “gas giants” Jupiter, Saturn, Uranus, and Neptune
“debris” – asteroids, comets and meteoroids, and some objects still being classified: Kuiper Belt, Oort cloud
How did these form?

20. Young Stars are forming in Orion top: visible photo shows the nebula bottom: IR photo shows the stars more clearly, note the four central stars (the Trapezium) see next slides

21. Young Stars in Orion visible photo shows the nebula

22. Young Stars in Orion IR photo shows the stars clearly, note the four central stars (the Trapezium)

23. Orion Nebula, A closer look reveals “knots” or “evaporating gaseous globules” EGGs, some of which may contain protostars.

24. These globules may contain evolving planets as well as the central protostar.

25. Several disks
that may be
protoplanetary
disks are found
after blowing up
the Hubble photo.

26. Major facts that any theory of solar-system formation must explain
Each planet is relatively isolated in space.
The orbits of the planets are nearly circular.
The orbits of the planets all lie in nearly the same plane.
Direction of planet’s movement in orbit is same as sun’s rotation.
Direction of planet’s rotation is same as sun’s rotation. (*usually*)
Direction of the various moon’s revolution is same as planet’s rotation.
The planetary system is highly differentiated.
Asteroids are very old, and not similar to terrestrial planets or Jovian planets.
The Kuiper belt is a group of asteroid-sized icy bodies orbiting outside the orbit of Neptune. (KBO – Kuiper Belt Objects)
The Oort Cloud is composed of icy cometary objects that do not orbit in the same plane as the planets (the ecliptic).

27. Angular Momentum influences the formation of planetary disks in the collapse of a cloud of gas

28. Beta Pictoris is one example of a protoplanetary disk top: false color image with the central star blocked out to show the disk bottom: artist’s rendition of what the disk might look like if a planet is forming

29. Beta Pictoris has a protoplanetary disk and a planet ! Image from ESO

30. Conservation of Angular Momentum

31. Conservation of Angular Momentum in a figure skater. (demo)

32. A Theory of Solar System Formation: a spinning gas cloud condenses to a much smaller size, and begins to rotate much faster due to conservation of angular momentum. This was the protoplanetary disk, also called a “proplyd.” This process explains the fact that all the objects tend to rotate (CCW) in the same way (or ‘sense’).

33. Jovian Condensation: due to whirlpools? Or accretion?

34. Differentiation may be due to the temperatures in the Early Solar Nebula The inner solar system is closer to the early Sun, and so it is hotter. Volatile gases are not condensed on the planets and end up condensing in the Jovian planets further out. This is similar to a process in chemical plants called distillation or fractionation.

35. Sun and Planets (approximate scale of diameters)

36. The Inner Solar System (sizes NOT to scale) link

37. The Scale of the Solar System
To appreciate the scale of the solar system, it is useful to make a scale model.
There is a spreadsheet-like form to make your own scale model of the solar system at

40. Extrasolar planets Planets have been discovered orbiting other stars.
See the PowerPoint file “day08exo.ppt” for the slides on this topic.