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Lecture 21

Outline For Rest of Semester• Oct. 29th Chapter 9 (Earth)• Nov 3rd and 5th Chapter 9 and Chapter 10 (Earth and Moon)• Nov. 10th and 12th Mars, Venus, and Mercury• Nov. 17th and 19th Jupiter and Saturn• Nov 24th Uranus and Neptune• Nov 26th Thanksgiving• Dec. 1st - Exam 3• Dec. 3rd – Pluto, and the Kuiper Belt• Dec. 8th and 10th – Chapter 7 and 8 (Comparative Planetology I and II)• Tuesday December 15th (7:30 am – 10:15 am) Final Exam• No Reading days are scheduled this semester• Exam Period begins at 7:30 a.m. on Monday, December 14 and ends on

December 21

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

Questions

• On posting “(with answers)” notes

• NASA finding water on the moon

• Why so many questions?

•  I have not had a chance to post Quiz solutions in ppt recently

• #18 “made no sense”

#18 Mars’ Atmosphere

• Why does Earth have oxygen in its atmosphere while Mars does not?

Venus Greenhouse

• The so-called greenhouse effect, which produces very high temperatures on the surface of Venus, is …

The absorption of CO2 gas by the planet’s atmosphere of infrared radiation emitted by its surface.

Mercury Elongation

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

It is difficult to see!

http://homepage.ntlworld.com/mjpowell/Astro/Naked-Eye-Planets/Naked-Eye-Planets.htm

• Why is the ecliptic at an angle with respect to the horizon?

Typo?

• More than 1200 Earth’s would fit inside Jupiter

• Jupiter is 11 times larger in diameter than Earth

Typo? No!

• More than 1200 Earth’s would fit inside Jupiter

• Jupiter is 11 times larger in diameter than Earth

V ~ R3 ~ D3 = (pi/6)D3

VEarth ~ D3Earth

VJupiter ~ (11*DEarth)3 ~ (11)3 D3Earth~ 1300 D3

Earth

Inferior planets

superior planets

A planet’s synodic period is measured with respect to the Earth and the Sun (for example, from one opposition to the next)

Periods

• Rotational

• Orbital

• Sidereal

• Synodic

Measured with respect to something that is not rotating or orbiting

Orbit

• http://learning.nd.edu/orbital/orbitals.swf

Extra-credit in-class Quiz

Use cell phone if

• If you have free text plan and

• Don’t mind receiving ads

otherwise

Use notecard and hand in at end of class

Register for quiz 2

Text to 41411:

astr111 2 rweigel

You will receive either one or two texts in response

Replace with your GMU email name

Question

• Which is longer, Jupiter’s synodic or orbital period?

• Which is longer, Jupiter’s synodic or Saturn’s synodic period?

• Guess Jupiter’s and Saturn’s synodic period.

• Which is longer, Jupiter’s synodic or orbital period?

• Which is longer, Jupiter’s synodic or Saturn’s synodic period?

• Guess Jupiter’s and Saturn’s synodic period.

2 1 a Synodic, Jupiter’s, longer than Earth’s2 1 b Synodic, Saturn’s, longer than Earth’s2 1 c Synodic, Saturn’s, shorter than Earth’s2 1 d Synodic,Jupiter’s, shorter than Earth’s2 1 e Orbital, Jupiter’s, longer than Earth’s

2 1 g Orbital, Saturn’s, longer than Earth’s2 1 f Orbital, Jupiter’s, longer than Earth’s

2 1 h Orbital, Saturn’s, longer than Earth’s

Question

• Which is longer, Jupiter’s synodic or orbital period? orbital

• Which is longer, Jupiter’s synodic or Saturn’s synodic period? Jupiter’s

• Guess Jupiter’s and Saturn’s synodic period. A little longer than Earth’s orbital period.

Time to repeat from Earth’s perspective

Kepler’s Third Law

P2 = a3

P = planet’s sidereal period, in yearsa = planet’s semimajor axis, in AU

Long orbital periods of Jupiter and Saturn cause favorable viewing times

to shift

What is wrong with either of these tables?

What is wrong with either of these tables?

Correct

The best time to observe Saturn from Earth is when it is

A. at opposition and it is midnight at your location on Earth.

B. at opposition and it is sunset or sunrise at your location on Earth.

C. at conjunction and it is midnight at your location on Earth.

D. at conjunction and it is sunset or sunrise at your location on Earth.

E. at opposition and it is just before sunrise at your location on Earth.

2 2

2 2

2 2

2 2

2 2

The best time to observe Saturn from Earth is when it is

A. at opposition and it is midnight at your location on Earth.

B. at opposition and it is sunset or sunrise at your location on Earth.

C. at conjunction and it is midnight at your location on Earth.

D. at conjunction and it is sunset or sunrise at your location on Earth.

E. at opposition and it is just before sunrise at your location on Earth.

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

What happens to ornaments when hoop is spun?

hoop

hoop

A B

C D

2 3

2 2

2 2

2 2

How to get Oblatehoop

The farther away from the axis, the more “thrown out” it gets.

Extra-credit in-class Quiz

Use cell phone if

• If you have free text plan and

• Don’t mind receiving ads

otherwise

Use notecard and hand in at end of class

All questions (correct or incorrect) worth 20 points (about two quiz questions).

Register for quiz 3

Text to 41411:

astr111 3 rweigel

You will receive either one or two texts in response

Replace with your GMU email nameNOT G NUMBER!

Both have arms attached to ears and shoulders. When they spin, which pair of arms swings out the most? Least?

a.X Most, Y Leastb.Y Least, X Mostc. W Most, Y Leastd.X,Y,Z Most, W Leaste.W Most, X, Y, Z Least

W W

X X

YY

Z Z

3 13 1 3 1

3 13 1

Both have arms attached to ears and shoulders. When they spin, which pair of arms swings out the most? Least?

a.X Most, Y Leastb.Y Least, X Mostc. W Most, Y Leastd.X,Y,Z Most, W Leaste.W Most, X, Y, Z Least

W W

X X

YY

Z Z

3 13 1 3 1

3 13 1

The farther away from the axis, the more “thrown out” it gets.

Both have arms attached to ears and shoulders. When they spin, which pair of arms swings out the most? Least?

All red arms are same distance from spin axis.Black arms are closer.Red arms swing out most.Black arms wing out least.

The oblateness of Jupiter and Saturn reveals their rocky cores

• Jupiter probably has a rocky core several times more massive than the Earth

• The core is surrounded by a layer of liquid “ices” (water, ammonia, methane, and associated compounds)

The oblateness of Jupiter and Saturn reveals their rocky cores

• On top of this is a layer of helium and liquid metallic hydrogen and an outermost layer composed primarily of ordinary hydrogen and helium

• Saturn’s internal structure is similar to that of Jupiter, but its core makes up a larger fraction of its volume and its liquid metallic hydrogen mantle is shallower than that of Jupiter

Metallic hydrogen inside Jupiter and Saturn endows the planets with strong magnetic

fields

• Jupiter and Saturn have strong magnetic fields created by currents in the metallic hydrogen layer

• Jupiter’s huge magnetosphere contains a vast current sheet of electrically charged particles

• Saturn’s magnetic field and magnetosphere are much less extensive than Jupiter’s

Jupiter and Saturn have extensive magnetospheres

• The Jovian magnetosphere encloses a low-density plasma of charged particles• The magnetosphere exists in a delicate balance between pressures from the

plasma and from the solar wind• When this balance is disturbed, the size of the magnetosphere fluctuates

drastically

Synchrotron Radiation

Charged particles in the densest portions of Jupiter’s magnetosphere emit synchrotron radiation at radio wavelengths

Golf!

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

Atmospheres

• gravity and escape velocity

Atmospheres

• gravity and escape velocity

Atmospheres• The visible “surfaces” of

Jupiter and Saturn are actually the tops of their clouds

Atmospheres• The rapid rotation of the

planets twists the clouds into dark belts and light zones that run parallel to the equator

The chemical composition of Jupiter and Saturn is difficult to

measure. Why?

Atmospheres• The outer layers of both

planets’ atmospheres show differential rotation– The equatorial regions

rotate slightly faster than the polar regions

Atmospheres• For both Jupiter and

Saturn, the polar rotation rate is nearly the same as the internal rotation rate

Spacecraft images show remarkable activity

in the clouds of Jupiter and Saturn

Video

• Chapter 14 videos

• http://bcs.whfreeman.com/universe7e

Storms

• Both Jupiter and Saturn emit more energy than they receive from the Sun

• Presumably both planets are still cooling

• The colored ovals visible in the Jovian atmosphere represent gigantic storms

• Some, such as the Great Red Spot, are quite stable and persist for many years

Storms in Saturn’s atmosphere seem to be shorter-lived

The internal heat of Jupiter and Saturn has a major effect on the

planets’ atmospheres

• Explain how Infrared and Visible (indicated on the previous slide) relate to the blackbody curves we studied.

• X-Ray image at airport

http://static.howstuffworks.com/gif/airport-security-xray2.jpg

A space probe has explored Jupiter’s deep atmosphere

• There are presumed to be three cloud layers in the atmospheres of Jupiter and Saturn

• The reasons for the distinctive colors of these different layers are not yet known

• The cloud layers in Saturn’s atmosphere are spread out over a greater range of altitude than those of Jupiter, giving Saturn a more washed-out appearance

Spacecraft images show remarkable activity

in the clouds of Jupiter and Saturn

In the news: Hurricane on Saturn?

• http://saturn.jpl.nasa.gov/multimedia/videos/video-details.cfm?videoID=136

• http://www.youtube.com/watch?v=dnF6PVSSSag – Hurricane-like vortex at Saturn's south pole,

where the vertical structure of the clouds is highlighted by shadows. Such a storm, with a well-developed eye ringed by towering clouds, is a phenomenon never before seen on another planet.

Both Jupiter and Saturn emit more energy than they receive from the Sun. What does this tell us?

Jupiter radiates more energy into space than it receives from the Sun. What is the primary source of the excess energy that Jupiter radiates?

A. Decay of radioactive materials in Jupiter's core

B. Tidal forces from Jupiter's moonsC. Jupiter is still contracting, and the

contraction releases energyD. Jupiter's rotation is slowing down

dramatically, and this slowdown releases energy

E. All of the above are the energy sources

3 2

3 23 2

3 2

3 2

Jupiter radiates more energy into space than it receives from the Sun. What is the primary source of the excess energy that Jupiter radiates?

A. Decay of radioactive materials in Jupiter's core

B. Tidal forces from Jupiter's moonsC. Jupiter is still contracting, and the

contraction releases energyD. Jupiter's rotation is slowing down

dramatically, and this slowdown releases energy

E. All of the above are the energy sources

3 2

3 23 2

3 2

3 2

What can you say about these planets?

• If both these planets formed at the same time, which would be expected to be warmer? Which would be expected to have more tectonic activity?Planet #1, Planet #1Planet #1, Planet #2Planet #2, Planet #2Planet #2, Planet #1

3 3 a3 3 b3 3 c

3 3 d

• If both these planets formed at the same time, which would be expected to be warmer? Which would be expected to have more tectonic activity?Planet #1, Planet #1Planet #1, Planet #2Planet #2, Planet #2Planet #2, Planet #1

3 3 a3 3 b3 3 c

3 3 d

If Jupiter and Saturn formed at the same time, which should be emitting more heat?

• Saturn’s atmosphere contains less helium than Jupiter’s atmosphere

• This lower abundance may be the result of helium raining downward into the planet

• Helium “rainfall” may also account for Saturn’s surprisingly strong heat output

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

• Link

Something is Fishy

• How can a planet be solid?

• Pebbles, snowballs and boulder size

• How was this determined?

• Videos 12.8-12.10

Earth-based observations reveal three broad rings encircling Saturn

• Saturn is circled by a system of thin, broad rings lying in the plane of the planet’s equator

• This system is tilted away from the plane of Saturn’s orbit, which causes the rings to be seen at various angles by an Earth-based observer over the course of a Saturnian year

Saturn’s rings are composed of numerous icy fragments, while Jupiter’s

rings are made of smallrocky particles

• The principal rings of Saturn are composed of numerous particles of ice and ice-coated rock ranging in size from a few micrometers to about 10 m

• Jupiter’s faint rings are composed of a relatively small amount of small, dark, rocky particles that reflect very little light

• Most of its rings exist inside the Roche limit of Saturn, where disruptive tidal forces are stronger than the gravitational forces attracting the ring particles to each other

• Each of Saturn’s major rings is composed of a great many narrow ringlets

Saturn’s rings consist of thousands of narrow,

closely spaced ringlets

Saturn’s inner satellites affect the appearance

and structure of its rings

The faint F ring, which is just outside the A ring, is kept narrow by the gravitational pull of shepherd satellites

Outline

• Jupiter and Saturn– Orbit

– Surface

– Atmosphere

– Rings

– Moons

Preview

• Already discussed influence on Saturn’s rings.

• Jupiter’s moons are even more interesting