ASTR1030 Lecture 37: Kepler's Laws, Newton's Laws, and Planetary Formation - Prof. Robert , Study notes of Astronomy

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ASTR1030 - FALL, 2008. LECTURE 37; PAGE 1

ASTR

http://lasp.colorado.edu/~ergun/

ASTR1030/

Final Exam: Saturday at 1:30 pm. In class.

Today

• Review

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 2

Kepler’s Laws

• Planets travel in an ellipse with the sun at one of the foci.• The planet sweeps out equal area in equal time. (The planet goes faster when

nearer the sun).

• [Orbital Period (years)]

2

= [Average Distance (AU)]

3

(3rd LAW ONLY VALID FOR BODIES ORBITING THE SUN!)

Newton’s Laws of Gravity

• Every mass attracts every other mass through a force called gravity.• The force between any two objects is proportional to the product of their

masses.

• The force of gravity decreases with the square of the distance between the

centers of the two objects.

G = 6.67x

-

m

3

/kg-s

2

F

G

M

1

M

2

d

2

---

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 4

Newton and Kepler

General Form

Escape Formula:

p

π

GM

Big

a

v

GMr

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 5

Light: The “Wave-Particle Duality”

Waves

:

Photons

h

= 6.626x

J-s

f Spectrum

λ ×

c =

E

hc -----^ λ

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 7

Light: Emission

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 8

Light

Doppler Shift

v - - c

λ

shift

λ

laboratory

• λ

laboratory

v

c

∆λλ

0

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 10

Nebular Theory

Physics of Collapsing Clouds • As the gas clouds collapse, they

heat up

; Gravitational energy is converted

into thermal energy.

• The clouds

spin up

just as an ice skater spins faster as she pulls in her hands.

This process is called

conservation of angular momentum

• The cloud

flattens

. Collisions play a major role in this process. The collaps-

ing process eventually leads to an “orderly” spinning disk called a

proto-

planetary disk

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 11

Planetary Formation

Materials of the Protoplanetary Disk • Metals• Rocks• Ices (Hydrogen Compounds)• Light Gas Important Point: The different materials condense at different temperatures.Metals and rocks can condense near the star (sun), but ices only can form faraway. Chemistry, Kepler, and collisions dominate this process.

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 13

Nebular Theory

• Collapse of an Interstellar Cloud• Star Birth• Formation of Planetesimals• Formation of Planets• Solar Wind: Clearing Away the Gas• Leftovers Bombardment

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 14

Radioactive Dating

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 16

Cooling of Terrestrial Planets

Basic Processes ofCooling •^

Convection:

Hot material

flows carrying thermalenergy with it.

-^

Conduction

: Heat flows

within a material. Thematerial does not move.

-^

Eruption

: In my mind, a

form of convection

-^

Radiation

: Conduction

and convection move heatto the surface. Ulti-mately, the energyescapes the planet byradiation, mostly in theinfrared.

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 17

Shaping the Surface of Terrestrial Planets

Basic Processes • Impact cratering• Volcanism• Tectonics• Erosion

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 19

Life?

• The earliest fossils on Earth are ~3.9 billion years old.• Bombardment dramatically reduced ~3.8 billion years ago.• The climate on Mars was substantially different ~3.5 billion years ago. It is

possible that the early atmosphere was warm enough for occasional precipi-tation and surface runoff. This idea is controversial.

• The change in climate since 3.5 billion years ago may have been caused by

atmospheric loss and condensation into the polar caps. Earth forms

Heavy bombardment ends -3.8 Gyr.

Mars volcanic activity ends -3.7 Gyr. Earliest fossils on Earth -3.9 Gyr.

Mars losses atmosphere -3.5 Gyr. Fossil evidence on Mars - 3.6 Gyr.

-4.5 Gyr

Now

ASTR1030 - FALL, 2008. LECTURE 37; PAGE 20

Planetary Atmospheres

Origin • Outgassing• Evaporation• Bombardment Loss • Thermal Escape• Bombardment• Atmospheric Cratering• Condensation• Chemical Reactions Structure • Exosphere• Thermosphere/Ionosphere (x-rays absorbed)• Stratosphere (UV absorbed)• Troposphere (partial IR absorption)