Exam Grades

1
Exam Grades
Due to the rush to get exams back, I did not
record credit for those who wrote out their own
answers. If you did write out your own answer to
a question, please bring me your exam so I can
update your score.
2
Announcements

• Note the exam questions were mostly taken from
  the quiz and assignments. It is therefore
  important to understand the questions, not just
  memorize the correct answer, since they will be
  asked differently.
• Assignments will have TWO parts (1) an
  application or practice of what you have learned,
  (2) questions about the reading for the next
  lecture.
• Planet Assignment 3, due Wednesday Feb 25,
• Part 1 Astronomy Place tutorial Formation of
  the Solar System
• Part 2 Angel Planet Assignment 3

3
Confusions Questions?

• Solar Nebula Theory - collapse heating
• What triggers the collapse
• How does it collapse
• What heats it up
• Asteroids - why are they between Mars Jupiter
• Dating rocks, radioactive decay
• Doppler Effect

4
What is a Planet?
An object that has a mass between that of Pluto
and the nuclear reaction threshold of 13 MJ   and
that forms in orbit around a star that generates
energy by nuclear reactions.
5
The Solar System
6
Solar System Properties

• Patterns of Motion
• All planets orbit the Sun in the same direction
  (as Sun spins), in nearly the same plane, in
  nearly circular orbit
• Two types of planets
• Terrestrial small, rocky, inner
• Jovian large, liquid H, He ices, outer
• Astroids Comets
• Comets dirty ice, Astroids rocks iron
• Ubiquitous impact craters
• All old solid surfaces
• Exceptions
• Uranus rotates sideways, Venus rotates backwards

7
Patterns of Motion
8
Two Types of Planets
Terrestrial small rocky, iron inner
Jovian large H, He, ices outer
9
Asteroid Comets
Dirty ice
Rocks iron
10
Ubiquitous Craters
Mars
Moon
Callisto
11
Solar System - How did it Form?What produced the
organized motions?

• Planets formed as part of the formation of the
  Sun.
• Begin with region of higher density composed of H
  He traces of heavier elements in the space
  between the stars (called interstellar cloud)
• Gravity makes the cloud collapse
• Triggered possibly by explosion of a nearby star

12
Collapse of Interstellar Cloud
Angular Momentum Is conserved. As cloud
collapses it spins faster.
13
Why are orbits in nearly same plane?
Collapses more along poles than in equator. Forms
a disk.
14
Why are orbits nearly circular?
15
Solar System - How did it Form?Why are there two
types of planets?

• Planets formed as part of the formation of the
  Sun.
• As cloud collapses gets hotter (falling
  converts gravitational potential energy to
  kinetic energy). Inner regions hotter than outer
  (fell farther).
• Rocks iron solid at high temperatures
• Ices solid only at low temperatures

16
Solidification Temperatures
17
Condensation Regions
18
Terrestrial Jovian Planets

• Close to Sun - rocks and iron are solidMake
  rocky terrestrial planets
• Far from Sun - Ices (water, carbon dioxide,
  methane, ammonia) are solidMake larger
  proto-planets withGravity large enough to
  attract H He gasMake Jovian planets

19
Terrestrial Jovian Planets
20
Gravity captures H He gas
21
Humans ( Earth) are made of the flotsam and
jetsam of the universe
22
Solar System - How did it Form?What are Comets
Asteroids?
Leftover planetesimals.
23
Asteroids

• Left over rocky iron planetesimals from
  formation of planets

24
Comets

• Left over icy planetesimals from formation of
  the Jovian planets

25
Solar System - How did it Form?
Why ubiquitous impact craters?
Remains of accretion of planetesimals.
26
Accretion of Planetesimals
27
Review of nebular theory
28
When did the Solar System Form?

• Measurements of decaying elements in meteorites
  indicate age of solar system
• 4.6 billion years

29
Thought Question

• Suppose you bought a carton of special eggs --
  each day half of the eggs in the carton hatch.
  You open the carton and find 9 chicks and 3 eggs.
  How long ago was it packed?
• A. Yesterday
• B. Two days ago
• C. Three days ago
• D. Last week

30
Example Half of all potassium-40 nuclei decay
into argon-40 every 1.25 billion years
31
What about Moons?
32
Moons of Jovian Planets form in miniature disks
33
Earths moon was probably created when a big
planetesimal tore a chunk out of the newly
forming Earth.
34
Collisionsimulation
35
Other Evidence?Other Planetary Systems

• Activity
• 1. Predict what you expect to be found about the
  properties of other planetary systems
• 2. We will then see what was actually found, and
  you will compare that with your predictions
• You will not be graded on the accuracy of your
  predictions, but on their relevance
  completeness.

36
How are Extrasolar Planets Detected?
By the Wobble they produce in their parent
star. Detection limit gt 0.3 MJupiter
37
Doppler Effect

• Analogy
• Suppose photons are busses on Grand River Ave.
  Busses come once every 10 min on average
• If you are walking East towards Okemos, will the
  busses heading west from Okemos pass you every 10
  min, or less or more?
• If you are walking West towards Lansing, will the
  busses heading west from Okemos pass you every 10
  min, or less or more?

38
What has been found?

• 120 Planets around Main Sequence (solar like
  stars)
• In 105 planetary systems
• 15 multiple planet systems

39
What has been found - Masses
40
What has been found - Eccentricity
Solar System Eccentricities lt 0.1 Except
Mercury Pluto
41
What has been found - Composition
42
What we expected What we found

• Nearly circular orbits
• Jovian planets far from star

• Highly eccentric orbits
• Jovian planets close to star

43
Implications for Life

• Eccentric Jovian planets will eject small
  terrestrial planets from the system.
• Migrating Jovian planets will eject small
  terrestrial planets as they pass.
• Young stars with more heavy elements are more
  likely to form planets than older stars with less
  heavy elements.

44
Questions?

• How are circular orbits produced? Are they
  typical or atypical?
• How are hot, close Jovian planets produced? Do
  they form as outer planets and migrate inward?
  What makes them migrate?