The Jovian PlanetsCOMPARISON OF SIZES:

Gas Giants Ice Giants

1. Distance from the Sun

2. Size & Mass

3. Chemical Composition

4. Rotation

5. Moons & Rings

…and what do extrasolar planets tell us?

Main differences between terrestrial and jovian planets:

1. Jovian planets follow circular orbits farther from Sun than terrestrial planets

• outermost terrestrial planet (Mars): 1.5 AU

• innermost Jovian planet (Jupiter): 5.2 AU

COMPARE ORBITS

jovian planets probably formed where icy material could condense

Orbits of Extrasolar Planets

• most detected planets have orbits smaller than Jupiter’s

• planets at greater distances are harder to detect…

star wobbles less wobble changes slowly “observational bias”

2. Jovian planets bigger and more massive than terrestrial planets

• 4 to 11 Earth’s size

• Each has more mass than all terrestrial planets

• Jupiter has more mass than ALL planets

More raw material available (ices, hydrogen and helium gases, as well as rock) for jovian planets

3. Jovian planets have different composition than terrestrial planets

ATMOSPHERES:• spectrums reveal mostly hydrogen compoundsDENSITY:• low densities require mostly hydrogen and helium

methane responsible for bluish colors

Jupiter

Clouds:

colors from materials condensing at different depths:

ammonia(NH3)

ammonium hydrosulfide (NH4SH),

water (H2O), DEEPEST

SHALLOWEST

Saturn

Uranus

Clouds -

• Methane (CH4) absorbs red light

Neptune“Great Dark Spot” – now gone

methane (CH4) ice clouds

Thought Question:How does the escape velocity for Saturn

(mass: 95 Mearth, radius 9.5 Rearth), compare to Earth’s?

A. about 20 times larger

B. about 20 times smaller

C. about 10 times larger

D. about 10 times smaller

E. about 3 times larger

F. about 3 times smaller

Thought Question:How does Uranus’ (about 4 Earth radii, 15

Earth masses) density compare to Jupiter’s (about 11 Earth radii, 318 Earth masses)?

(Enter the ratio rounded to one decimal place.)

Interiors• Jupiter, Saturn: probably formed first and captured more H and He

(closer to Sun, icy planetesimals and gas were common)

compressed metallic hydrogen probably causes large magnetic fields

• Uranus, Neptune: mostly compressed “icy” material

Extrasolar Planet Densitiesjovian planets in solar system: 0.7 - 1.7 g / cm3

jovian-mass extrasolar planets have wide range in densities: 0.1 - 9 g / cm3!

4. Jovian planets rotate faster than terrestrial planets

Earth: 24 hours

Jupiter: 9 hours 50 min (fastest)

Uranus: 17 hours 14 min (slowest)

jovian planets got a lot of angular momentum from gases they pulled in

Thought Question:What should happen to a rapidly spinning

planet if it is mostly made of materials that aren’t solid?

A. It will bulge outward at its equator.

B. It will bulge outward at its poles (like a football).

C. It will expand in all directions.

D. It will pull inward all over.

E. Nothing really - it will just spin normally.

Oblateness• “flattening” caused by planet’s rotation – shape is not a sphere• The more of the interior that is fluid, the more it will bulge at its

equator when it rotates

Example: tossing pizza

5. Jovian planets have many moons and rings

COMPARE

• Terrestrial planets:

Earth: 1 big moonMars: 2 asteroid-

sized moons

• Jovian planets:Many asteroid-

sized moons, some larger

Mostly ice, rock, or combination

5. Jovian planets have many moons and rings

• No terrestrial planets have rings

• All Jovian planets have rings

visibility of rings depend on how reflective they are

Light Waves… caused by accelerating electrial charges

wavelength (λ): distance between successive wave crests

different colors have different wavelengths:

frequency (f): number of wave crests that pass per second

units: number per second, or Hertz (Hz)

for sound waves, frequency = PITCH

speed of light (c):

WAVELENGTHWAVELENGTH

BLUERED

700 nm 400 nm

The Electromagnetic Spectrum

• visible light is just a small part of the entire spectrum:

increasing

f decreasing

Thought Question:What wavelength will radio waves from station

“90 FM” have? (FM station frequencies are given in mega-Hertz, or 106 Hz.)

(Enter the answer in m to two significant digits.)

Light Wavesenergy (E): higher frequency larger energy

WAVELENGTHWAVELENGTH

BLUERED

Thought Question:

SpectrumSPECTRUM: a way of describing a MIXTURE of light:

how intense are different colors?

Roughly equal mixture of colors appears WHITE:

LIG

HT

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

LIG

HT

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

Unbalanced mixtures are tinted by most intense colors:

Observing a SpectrumSELECT SPECIFIC

WAVELENGTH RANGES (FILTERS)

SPLIT LIGHT BY WAVELENGTH

(PRISMS, CDs)

greyscale (lighter = more intense)

Thought Question:If I project dots of red and green light on the

screen, what will you see where they overlap?

A. A yellow dot

B. A brown dot

C. A blue dot

D. A black dot

E. A white dot

If I project dots of blue, red, and green light on the screen, what will you see where they overlap?

The Importance of SpectrumsAtoms of each element …

absorb and emit unique combinations of colors AND work the same way across the universe

Spectrums can be used to:

identify chemicals

measure temperature

measure speeds

ABSORPTION

The Ring Nebula

1 LIGHT-YEAR

EMISSION

THERMAL RADIATION

Kinds of Spectrum

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

CONTINUOUS

INTEN

SIT

Y ABSORPTION LINE

INTEN

SIT

YEMISSION LINE

400 nm 700 nm

Kinds of SpectrumCONTINUOUS: hot, opaque materials emit thermal radiation

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

EXAMPLE GRAPH:

examples: light bulbs, you, stars (sort of)

Jupiter’s Moon Io

Jupiter’s Moon Io

Star Colors

Thermal Radiationhot, opaque objects radiate light in a way that depends only on

temperature• as T increases: light of all wavelengths gets brighter wavelength of most intense light gets shorter (bluer)

BLACK

(no visible light)

RED ORANGE YELLOW WHITE

WHAT WE SEE BY EYE:

Thermal RadiationStefan-Boltzmann Law: brightness at surface of hot object (also called flux)

(energy released per second per area)

FOR SAME AREA, HOT SURFACE RELEASES LIGHT FASTER

ALL COLORS GET MORE INTENSE

(a constant)

Thermal Radiation• thermal radiation is released at all

wavelengths, but…

Wien’s Law: most intense light is released at this wavelength:

HOTTER=BLUER

Sun:

Blackbody Applet

Temperature

INFRARED VIEWS ON EARTH (FALSE COLOR)

Police Video

SATURN (FALSE COLOR:

RED = INFRARED)

ULTRAVIOLET LIGHT SOURCES ON EARTH

Thought Question:The hottest stars can be more than ten times hotter than

the Sun at their surfaces. How much brighter (energy released per m2 per sec) would the surface of such a star be compared to the Sun?

What would the peak wavelength of such a star be (in nm) if the Sun’s peak is at around 500 nm?

Star Luminosity

Stars release THERMAL RADIATION: brightness of each piece of surface

only depends on temperature

Apply Stefan-Boltzmann Law:

flux from each piece of star’s surface

star’s surface area

• luminosity (L): total amount of energy released per time

units: Watt (W): 1 W = 1 J / s property of a star: its “power”

Thought Question:The graph below shows the blackbody

spectra for three different stars. Which of the stars is at the highest temperature?

A. Star A

B. Star B

C. Star C

Jupiter’s Moon Io

Thought QuestionWhat kind of spectrum would you see if you were

looking in the direction shown by the arrow?

A. continuous (thermal radiation) spectrum

B. absorption line spectrum

C. emission line spectrum

transparent gas cloud

star

Types of Spectrumtransparent gas

cloud

(atoms can absorb specific wavelengths

of light AND emit the same

wavelengths)

star

(source of thermal radiation

– frequent collisions

between electric charges)

ABSORPTION

THERMAL RADIATION

EMISSION

WHAT YOU SEE:

Thought Question:

When I pass a jug of clear blue liquid in front of the light bulb, what will happen?

A. The jug will make the violet, blue, and green light more intense.

B. The jug will make the yellow, orange, and red light more intense.

C. The jug will remove most of the violet, blue, and green light.

D. The jug will remove most of the yellow, orange, and red light.

Kinds of SpectrumABSORPTION LINE: transparent material in front of hotter opaque material

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

EXAMPLE GRAPH:

light is removed by cloud

examples: seeing stars through gas (like an atmosphere)

sodium

hydrogen

magnesium

iron

Sun

sodium

hydrogen

magnesium

iron

Arcturus

ORION NEBULA

(about 24 light-years across)

Kinds of SpectrumEMISSION LINE: hot transparent material in front of cool background

INTEN

SIT

Y

WAVELENGTHV I B G Y O R

EXAMPLE GRAPH:

light is released by cloud

examples: street lamps, fluorescent bulbs, interstellar gas clouds

Thought Question:

Which of the following patterns most closely resembles the pattern of lines you saw in the spectrum?

A.

B.

C.

D.

AtomsNUCLEUS: contains almost all of an atom’s mass

protons: positively-charged particles

neutrons: particles with no charge

ELECTRON CLOUD: electrical force keeps electrons near nucleus

electrons: negatively-charged particles

HYDROGEN HELIUM

More protons in nucleus means:

stronger electrical force

electrons more tightly bound to atom (on average)

Absorbing Light• Electron only absorbs light with correct amount of energy to move it to an allowed distance from nucleus

GROUND STATE-6

-3

-1

ELECTRON

ENERGY LEVELS:

WHAT HAPPENS IN ATOM:

electron moves farther from nucleus

2 UNITS OF ENERGY ABSORBED

Emitting Light• Electron releases exact amount of energy needed to drop it to

a smaller allowed distance from nucleus

GROUND STATE-6

-3

-1

ELECTRONENERGY LEVELS

WHAT HAPPENS IN ATOM:

electron moves closer to nucleus

3 UNITS OF ENERGY RELEASED

Energy Levels

allowednot allowed

E1

E2

E3

E4

E=0

electrons in atoms are only allowed to:• have specific amounts of total

energy• transition to other allowed energy

levels OR off the atom absorbed light will have characteristic E and :

n = 1

n = 2

n = 3n = 4

Thought Question:The electrons in an atom can be in the energy levels shown

below. If an electron is in the ground state (the level with an energy of -9 units), how many units of energy can the electron absorb and still remain attached to the atom?

(Enter ALL possible correct answers as one number, then hit send.)

Hydrogen:the simplest atom…

Balmer lines:

-13.6 eV

-3.4 eV

-1.5 eV

-0.8 eV

0 eV

E

nlo = 2nhi =3,4,5,…

nlo = 1nhi =2,3,4,…

Review QuestionIn what order do we think the following things

appeared in the solar system as it formed?A. snowflakes and dirt particlesB. Earth-sized protoplanetsC. rotating disk of gasD. asteroids and cometsE. large cloud of gas

Review Question:The choices below describe 4 hypothetical planets. Which planet

surface would you expect to be least crowded with impact craters? (Assume they orbit a star just like the Sun and are the same age as the planets in our solar system.)

Size Distance from Sun Rotation Rate

A. same as Venus same as Mars every 25 hours

B. same as Moon same as Mars every 10 days

C. same as Mars same as Earth every 10 hours

D. twice Earth size same as Mercury every 6 months

Review QuestionThe image below shows a picture of Mare Imbrium

on the Moon. Put the following features in order from oldest to youngest: A) Imbrium lava, B) Sinus Iridium, C) the Apennine mountains?

Review QuestionIf you decreased the temperature of a star, would the

following A) increase, B) decrease, or C) stay the same?

the intensity of the color red? the intensity of the color blue? the wavelength of the most intense color?