Transcript Week 9

The Jovian Planets
COMPARISON OF SIZES:
Gas Giants
Ice Giants
Main differences between
terrestrial and jovian planets:
1.
2.
3.
4.
5.
Distance from the Sun
Size & Mass
Chemical Composition
Rotation
Moons & Rings
…and what do extrasolar planets tell us?
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 compounds
DENSITY:
• low densities require mostly hydrogen and helium
methane
responsible
for bluish
colors
Jupiter
SHALLOWEST
DEEPEST
Clouds:
colors from materials
condensing at different
depths:
ammonia(NH3)
ammonium hydrosulfide
(NH4SH),
water (H2O),
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
2GM
vesc =
R
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 Densities
jovian 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.
B.
C.
D.
E.
It will bulge outward at its equator.
It will bulge outward at its poles (like a football).
It will expand in all directions.
It will pull inward all over.
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 moon
Mars: 2 asteroidsized moons
• Jovian planets:
Many asteroidsized 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:
RED
BLUE
700 nm
400 nm
WAVELENGTH
WAVELENGTH
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):
c = lf = 3 ´10 m/s
8
The Electromagnetic Spectrum
• visible light is just a small part of the entire spectrum:
1 nm =10-9 m

f
increasing
decreasing
Thought Question:
What wavelength will radio waves from
station “90 FM” have? (FM station
frequencies are given in mega-Hertz, or
106 Hz.)
c = l f = 3.00 ´10 m/s
8
(Enter the answer in m to two significant digits.)
Light Waves
energy (E): higher frequency  larger energy
E = hf
h = 6.63 ´10
RED
-34
J ×s
BLUE
WAVELENGTH
WAVELENGTH
Spectrum
Unbalanced mixtures are
tinted by most intense
colors:
V
I
B
G Y O R
WAVELENGTH
V
I
B
G Y O R
WAVELENGTH
LIGHT
INTENSITY
Roughly equal mixture of
colors appears WHITE:
LIGHT
INTENSITY
SPECTRUM: a way of describing a MIXTURE of light:
how intense are different colors?
Observing a Spectrum
SPLIT LIGHT BY
WAVELENGTH
(PRISMS, CDs)
SELECT SPECIFIC
WAVELENGTH
RANGES (FILTERS)
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
The Importance of Spectrums
Atoms 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
EMISSION
The Ring Nebula
1 LIGHT-YEAR
THERMAL
RADIATION
CONTINUOUS
ABSORPTION
LINE
INTENSITY
INTENSITY
INTENSITY
Kinds of Spectrum
V I B G Y O
400 nm
WAVELENGTH
EMISSION
LINE
R
700 nm
Kinds of Spectrum
CONTINUOUS: hot, opaque materials emit thermal radiation
examples: light bulbs,
you, stars (sort of)
INTENSITY
EXAMPLE GRAPH:
V
I
B
G Y O R
WAVELENGTH
Jupiter’s
Moon Io
Jupiter’s
Moon Io
Star
Colors
Thermal Radiation
hot, 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)
WHAT WE SEE BY EYE:
BLACK
(no visible light)
RED
ORANGE
YELLOW
WHITE
Thermal Radiation
Stefan-Boltzmann Law: brightness at surface
of hot object (also called flux)
(energy released per second per area)
(a constant)
FOR SAME AREA, HOT SURFACE
RELEASES LIGHT FASTER
ALL COLORS GET MORE
INTENSE
Thermal Radiation
• thermal radiation is released at all
wavelengths, but…
Wien’s Law: most intense light is
released at this wavelength:
lpeak
(2.9 ´10 6 nm× K)
»
T
HOTTER=BLUER
T = 5800 K
Sun:
lmax = 500 nm
Temperature
T ( K ) = T ( C ) + 273
INFRARED
VIEWS ON
EARTH
(FALSE COLOR)
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?
lpeak
(2.9 ´106 nm × K )
»
T
Star Luminosity
• luminosity (L): total amount of energy released per time
units: Watt (W): 1 W = 1 J / s
 property of a star: its “power”
Stars release THERMAL RADIATION:
 brightness of each piece of surface
only depends on temperature
 Apply Stefan-Boltzmann Law:
star’s surface
area
flux from each
piece of star’s
surface
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 Question
What 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
star
transparent
gas cloud
Types of Spectrum
star
transparent gas cloud
(source of thermal
radiation – frequent
collisions between
electric charges)
(atoms can absorb specific
wavelengths of light AND
emit the same wavelengths)
WHAT YOU SEE:
ABSORPTION
THERMAL RADIATION
EMISSION
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 Spectrum
ABSORPTION LINE: transparent material in front of hotter opaque material
examples:
seeing stars
through gas
(like an
atmosphere)
light is removed by
cloud
INTENSITY
EXAMPLE GRAPH:
V
I
B G Y O R
WAVELENGTH
Sun
hydrogen
sodium
magnesium
iron
Arcturus
hydrogen
sodium
magnesium
iron
ORION NEBULA
(about 24 light-years across)
Kinds of Spectrum
EMISSION LINE: hot transparent material in front of cool background
examples: street
lamps, fluorescent
bulbs, interstellar gas
clouds
light is released by
cloud
INTENSITY
EXAMPLE GRAPH:
V
I
B
G Y O R
WAVELENGTH
Thought Question:
Which of the following
patterns most
closely resembles
the pattern of lines
you saw in the
spectrum?
A.
B.
C.
D.
Atoms
NUCLEUS: 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
ENERGY
LEVELS:

-1
2 UNITS OF ENERGY
ABSORBED
-3
-6
ELECTRON
GROUND STATE
WHAT
HAPPENS IN
ATOM:
electron moves
farther from
nucleus
Emitting Light
• Electron releases exact amount of energy needed to drop it to
a smaller allowed distance from nucleus

ENERGY
LEVELS
-1
ELECTRON
-3
3 UNITS OF ENERGY
RELEASED
-6
GROUND STATE
WHAT
HAPPENS IN
ATOM:
electron moves
closer to
nucleus
Energy Levels
E=0
n=4
n=3
E4
n=2
E2
n=1
E1
not allowed
E3
allowed
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 :
llo®hi
hc
=
Ehi - Elo
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:
E
0 eV
the simplest atom…
-0.8 eV
-1.5 eV
13.6 eV
En = n2
n = 1,2,3,...
-3.4 eV
nlo = 2
nhi =3,4,5,…
-13.6 eV
nlo = 1
nhi =2,3,4,…
Balmer lines:
1 eV = 1.6 ´10-19 J
æ 1
1
1 ö
çç 2 - 2 ÷÷
=
l 91.2 nm è nlo nhi ø
1
Review Question
In what order do we think the following things
appeared in the solar system as it formed?
A.
B.
C.
D.
E.
snowflakes and dirt particles
Earth-sized protoplanets
rotating disk of gas
asteroids and comets
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 Question
The 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 Question
If 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?