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Grades will be posted in MyUCFGrades
Quiz for Ch. 6 has been posted and is due next Mon. night (as usual)
I. Overall Properties of Solar System and its Formation
II. Extrasolar Planets
Outline Ch.6 Solar System (Different from Book’s outline)
I. Overall Properties of Solar System:1. Nearly co-planar orbits (disk-shaped)2. All planets orbit Sun in same direction as
Sun’s rotation3. MOST (but not all) planets rotate in same
direction as their obits around Sun4. Planets: Small dense terrestrial planets in inner SS Large, low density, Jovian planets in outer
SS Pluto is exception
(Cont.)
Outline Ch.6: Solar System (Different from Book’s outline)
I. Overall Properties (cont):5. In general: closer to Sun, larger density6. Hot near Sun cold far away7. Composition of Solar Nebula
Outline Ch.6 (Cont.)
The planets are tiny compared to the distances between them (a million times smaller than shown here), but theyexhibit clear patterns of composition and motion.
The patterns are more important than numbers, names, and other details
What have we learned?
• What does the solar system look like?
Our solar system consists of the Sun, nine eight planets and their moons, and vast numbers of asteroids and comets. Each world has its own unique character, but there are many clear patterns among the worlds.
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Clues to the Formation of Our Solar SytemOur Goals for Learning
• What features of our solar system provide clues to how it formed?
• What theory best explains the features of our solar system?
What have we learned?• What features of our solar system provide clues to how it
formed? Four major features provide clues:
(1) Planets all orbit the Sun in same direction as Sun’s rotation (counterclockwise when seen from North), most planets rotate in same direction as their orbit.
(2) The major planets divide clearly into two groups: terrestrial and jovian (Jupiter-like).
(3) The solar system contains large numbers of asteroids and comets.
(4) There are some notable exceptions to these general patterns.
What have we learned?• What theory best explains the features of our
solar system?
The nebular theory, which holds that the solar system formed from the gravitational collapse of a great cloud of gas.
Solar Nebula: rotating, disk-shaped
cloud out of which Sun and planets
formed
Slowly rotating interstellar cloud of
gas and dust collapses to form the Solar
Nebula
7. Composition of Solar Nebula:98% Hydrogen & Helium, 2% all other elementsCondensation of solids from nebula:
Inner part is hot, only high density materials (metals and silicates) can condense
Outer regions cooler, can condense lower density materials like water ice and other ices
I. Overall Properties (cont):
Condensation of Solids from Solar Nebula
(not exactly like the book)
Asteroids and comets
accreted at different distances
from the Sun, resulting in different ice
contents
What have we learned?
• Where did the solar system come from?
The cloud of gas that gave birth to our solar system was the product of recycling of gas through many generations of stars within our galaxy. This gas consisted of 98% hydrogen and helium and 2% everything else combined.
What have we learned?
• What caused the orderly patterns of motion in our solar system?
A collapsing gas cloud naturally tends to heat up, spin faster, and flatten out as it shrinks in size. Thus, our solar system began as a spinning disk of gas. The orderly motions we observe today all came from the orderly motion of this spinning disk of gas.
What factors do you think might have contributed to the difference between Terrestrial and Jovian Planets:a) Temperature (hotter near Sun and colder far
from Sun)
b) Size of Orbits (larger orbits can “sweep” more material)
c) The composition of the Solar Nebula
Question 1
What factors do you think might have contributed to the difference between Terrestrial and Jovian Planets:a) Temperature (hotter near Sun and colder far
from Sun)
b) Size of Orbits (larger orbits can “sweep” more material)
c) The composition of the Solar Nebula
d) All of the above
Question 1
How did the composition of the Solar Nebula affect the composition of the planets?1. Metals and Silicates can condense at higher
temperatures than water and other gases
2. Hydrogen, helium, and oxygen were more abundant than metals and silicates
3. The higher the mass a planet has, the larger the atmosphere it can retain.
The correct answer is
A. 1 and 2 C. 3 only
B. 1 only D. 1, 2 and 3
Question 2
How did the composition of the Solar Nebula affect the composition of the planets?1. Metals and Silicates can condense at higher
temperatures than water and other gases
2. Hydrogen, helium, and oxygen were more abundant than metals and silicates
3. The higher the mass a planet has, the larger the atmosphere it can retain.
The correct answer is
A. 1 and 2 C. 3 only
B. 1 only D. 1, 2 and 3
Question 2
7. Composition of Solar Nebula:98% Hydrogen & Helium, 2% other elementsCondensation of solids from nebula:
Inner part is hot, only high density materials (metals and silicates) can condense
Outer regions cooler, can condense lower density materials like water ice and other ices
Near Sun: terrestrial planetsFar from: Sun Jovian planets
I. Overall Properties (cont):
If I tell you a planet has many moons is it likely to bea) Terrestrial
b) Jovian
c) Pluto
d) an asteroid
Question 3
What have we learned?• Why are there two types of planets? Inner solar system: high temperatures, only
metal and rock could condense. Outer solar system: cold temperatures, more
abundant ices condense along with metal and rock.
What have we learned?• Where did asteroids and
comets come from? Asteroids are the
rocky leftover planetesimals of the inner solar system, and comets are the icy leftover planetesimals of the outer solar system.
• How do we explain the existence of our Moon and other “exceptions to the rules”?
•Most of the exceptions probably arose from collisions or close encounters with leftover planetesimals, especially during the heavy bombardment that occurred early in the solar system’s history. Our Moon is probably the result of a giant impact between a Mars-size planetesimal and the young Earth.
What have we learned?
• When did the planets form?
The planets began to accrete in the solar nebula about 4.6 billion years ago, a fact we determine from radioactive dating of the oldest meteorites.
6.5 Other Planetary Systems
Our Goals for Learning
• How do we detect planets around other stars?
• What have other planetary systems taught us about our own?
II. Extrasolar Planets Are there planets around other stars? Have we “seen” them?
Outline Ch.6 (Cont.)(Different from Book’s outline)
II. Extrasolar Planets Are there planets around other stars?
YES, about 1000! Have we “seen” them?
Outline Ch.8 (Cont.)
II. Extrasolar Planets Are there planets around other stars?
YES about 1000! Have we “seen” them?
We have not seen most of them (not directly), we have “seen” only a few so far
Outline Ch.8 (Cont.)
II. Extrasolar Planets About 1000 detected so far We have not “seen” most of them
yet, they are detected indirectly using radial velocity and transits in front of stars
Types of planets: all strange (because those are the only ones we can detect)
No Earth-sized extraterrestrial planet yet
Outline Ch.8 (Cont.)
More than 1000 known extrasolar planets as of Feb. 2011•Most are more massive than Jupiter and closer to their star than Earth is to Sun•Are revisions to the nebular theory are necessary? Some•Planets can apparently migrate inward from their birthplaces.
Orbits of 3 planets around star Upsilon Andromeda
Is Earth Unusual?
Only 5 Earth-like planets found so far
Observations are not good enough to tell if they are common or rare
Available methods can detect mainly BIG planets so far.
What have we learned?• How do we detect planets around other stars? We detect extrasolar planets primarily
indirectly by observing the planet’s effects on the star it orbits.
Most of the discoveries to date have been made with the Doppler technique, in which Doppler shifts reveal the gravitational tug of a planet (or more than one planet) on a star.
A a few planets have been observed to “transit” in front of their star.
What have we learned?
• What have other planetary systems taught us about our own?
Planetary systems exhibit a surprising range of layouts, suggesting that jovian (Jupiter-like) planets sometimes migrate inward from where they are born. This lesson has taught us that despite the successes of the nebular theory, it should be refined.
