Astr 1050    Wed., Dec. 11, 2002

   Today: Course Evaluations

                       Chapter 18, Jovian Planets

Chapter 18: Worlds of the Outer Solar System

Jupiter

Condensation model

Atmospheric winds

Atmospheric chemistry

Magnetic fields

Other Jovian Planets (Saturn, Uranus, Neptune)

will only cover major differences from Jupiter

Satellites (i.e. Moons)

Jovian Planets

Details of the atmosphere

Mostly made of H, He

Trace amounts of C, N, O, S

CH₄ present as gas

NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds

Colors from unknown trace chemicals

Density of gas smoothly increases with depth till point where it is indistinguishable from liquid
Þ no real “surface”

At very high temperatures and pressures hydrogen becomes a “metal” and conducts electricity
Þ generates magnetic field

Jupiter as seen by Cassini

Winds on Jupiter

Jupiter-Cassini Movie Mercator Projection

Winds near the Great Red Spot

Air circulation for very slowly rotating planet

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Hurricanes exist because
Low Pressure trying to turn winds to the left
almost balance
Coriolis Force trying to turn winds to the right.

Comparison of atmospheres

Jupiter has multiple cloud decks as air rises in low pressure “zones”

Mostly made of H, He

Trace amounts of C, N, O, S

CH₄ present as gas

NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds

Colors from unknown trace chemicals

Magnetic fields and trapped particles

Satellites orbiting through radiation belts lose particles which become ionized and trapped.

Aurora on Jupiter

Jovian Planets

Comparison of Jovian Planets

Variation in distance presumably ultimate causes other effects

P:      Kepler’s third law

T:      Falloff mostly just result of falling solar energy

But Neptune hotter because more internal heat

M:     Clue to details of solar nebula mode

Less material in outer solar system – or perhaps less efficient capture

r:      Should drop with mass because less compression

Works for Saturn vs. Jupiter

Increase for Uranus, Neptune indicates less H, He and more heavy material

Effects of T (and E) on Atmospheres

Saturn’s bands much less distinct than Jupiter’s

Temp. lower on Saturn Þ cloud condense lower

Deeper clouds Þ markings less visible

Differences at Uranus and Neptune

Even colder Þ clouds even deeper

So cold CH₄ can condense

Little solar energy to drive weather

Uranus has strange seasons – tipped on its side

Neptune has strong internal heat source,
so it still can have weather

Large amounts of heavy elements compared to amount of H, He on Jupiter, Saturn

Large amounts of CH₄ gas absorb red,
make planets appear blue

Implications of M, r for nebula

Relative amount of H, He (compared to heavy elements) drop for Saturn
then drop dramatically at Uranus and Neptune

Why were these outer planets so less efficient at capturing H, He?

Their mass is still great enough to do this, especially given low temperatures
in the outer solar system

May be a problem of timing

Accretion takes longer in the outer solar system because

The velocities of all objects there are much less

The distances between objects are greater

This is the same reason the periods of the orbits are so long

Uranus and Neptune may have only started to grow to critical size by the time the H, He gas was being driven out of the solar system

The Jovian planets are miniature solar systems

Because planets captured gas as they were forming
they had small “solar” nebulae Þ tests of nebula theory

Regular satellite systems

Large moons in direct (i.e. counterclockwise), equatorial orbits

Preserve solid material from time of formation

Jupiter shows solar-system like density gradients

Rings

Moons unusual and interesting objects in their own right

Io – most volcanically active body in solar system

Europa – may have liquid water ocean (and life!)

Titan – only satellite with a thick atmosphere

Many properties are due to tidal forces and resonances

The Roche Limit
When can tides tear a moon apart?

As a planetary body get close to another object, tidal forces distort the body more and more.

Remember, Earth raises tides on the Moon
just like it raises tides on the Earth

If the distortion gets large enough, the moon will be pulled apart

Happens at “Roche Limit” when moon is
~2.44 ´ radius of planet away

At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down

Only matters for objects held together by gravity

Astronaut in orbit will not be pulled apart

Is held together by much stronger chemical forces

Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle

Saturn as seen by the Hubble Space Telescope

Rings are individual particles all orbiting separately

Each particle – dust to golf ball to boulder size –
is really a separate moon on its own orbit

Orbit with Keplerian velocities: high in close, slow farther out

Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up

Structure in rings largely caused by gravity of moons

Resonances: Properly timed gravitational “pushes”

Like someone pushing kid on a swing

Timing of pushes just as important as force used

Pushing at random times has little effect

Pushing at just right point in each cycle can produce big effect

Cassini division at 1:2 resonance with Mimas

Comparison of Rings

All within Roche limit

Details controlled by Resonances and Shepard Satellites

Jupiter as a miniature solar system

Four large moons (Io, Europa, Ganymede, Callisto)

Regular (equatorial, circular) orbits

Pattern of changing density and composition with distance

Inner two (Io, Europa) mostly rocky

Outer two (Ganymede, Callisto) more icy

Io, Europa break rules about activity

Io most volcanically active body in solar system

Europa shows new icy surface with few craters

Tidal heating explains activity

Large tides from Jupiter flex satellites

Friction from flexing heats interiors

Important for Io, Europa, some other outer solar system satellites

Possible H₂O ocean on Europa

Tidal heating may keep H₂O liquid under ice cover

Perhaps a location where life could evolve

“Europa Orbiter” Mission being planned to determine if ocean exists

Callisto not active

Comparison of Satellites

Titan

Largest moon of Saturn

Has thick atmosphere

Pressure ~ 1 earth atmosphere

Mostly N₂, some CH₄

Gas held because of low T

UV acting on CH₄ Þ smog

Ethane produced – Lakes?

Can “see” surface only in IR

Cassini will drop probe in Fall 2004

“Code of the Lifemaker” by James P. Hogan, good sf

Triton

Largest moon of Neptune

In unusual retrograde orbit

Probably captured after it formed

Tides during capture may have caused heating

Does have thin atmosphere

Shows recent “activity”

Not volcanic – rather volatile related

Ices migrate with seasons

“Geysers” caused by heated ices


Jupiter
		Condensation model
		Atmospheric winds
		Atmospheric chemistry
		Magnetic fields
	Other Jovian Planets (Saturn, Uranus, Neptune)
		will only cover major differences from Jupiter
	Satellites (i.e. Moons)


	Mostly made of H, He
	Trace amounts of C, N, O, S
	CH₄ present as gas
	NH₃, NH₄SH, H₂O can condense in colder upper regions Þ clouds
	Colors from unknown trace chemicals
	Density of gas smoothly increases with depth till point where it is indistinguishable from liquid Þ no real “surface”

	At very high temperatures and pressures hydrogen becomes a “metal” and conducts electricity Þ generates magnetic field


Variation in distance presumably ultimate causes other effects
	P: Kepler’s third law
	T: Falloff mostly just result of falling solar energy
		But Neptune hotter because more internal heat
	M: Clue to details of solar nebula mode
		Less material in outer solar system – or perhaps less efficient capture
	r: Should drop with mass because less compression
		Works for Saturn vs. Jupiter
		Increase for Uranus, Neptune indicates less H, He and more heavy material


Saturn’s bands much less distinct than Jupiter’s
	Temp. lower on Saturn Þ cloud condense lower
	Deeper clouds Þ markings less visible

Differences at Uranus and Neptune
	Even colder Þ clouds even deeper
	So cold CH₄ can condense

	Little solar energy to drive weather
		Uranus has strange seasons – tipped on its side
		Neptune has strong internal heat source, so it still can have weather

	Large amounts of heavy elements compared to amount of H, He on Jupiter, Saturn
		Large amounts of CH₄ gas absorb red, make planets appear blue


Relative amount of H, He (compared to heavy elements) drop for Saturn then drop dramatically at Uranus and Neptune





Why were these outer planets so less efficient at capturing H, He?
	Their mass is still great enough to do this, especially given low temperatures in the outer solar system
May be a problem of timing
	Accretion takes longer in the outer solar system because
		The velocities of all objects there are much less
		The distances between objects are greater
		This is the same reason the periods of the orbits are so long

	Uranus and Neptune may have only started to grow to critical size by the time the H, He gas was being driven out of the solar system


Because planets captured gas as they were forming they had small “solar” nebulae Þ tests of nebula theory
	Regular satellite systems
		Large moons in direct (i.e. counterclockwise), equatorial orbits
		Preserve solid material from time of formation
		Jupiter shows solar-system like density gradients
	Rings

Moons unusual and interesting objects in their own right
	Io – most volcanically active body in solar system
	Europa – may have liquid water ocean (and life!)
	Titan – only satellite with a thick atmosphere

Many properties are due to tidal forces and resonances


As a planetary body get close to another object, tidal forces distort the body more and more.
	Remember, Earth raises tides on the Moon just like it raises tides on the Earth

If the distortion gets large enough, the moon will be pulled apart
	Happens at “Roche Limit” when moon is ~2.44 ´ radius of planet away
	At that point, tidal force pulling up on surface of moon is greater than moon’s gravity pulling down

Only matters for objects held together by gravity
	Astronaut in orbit will not be pulled apart
		Is held together by much stronger chemical forces
	Astronaut standing on the outside of the shuttle, hoping the shuttle’s gravity would hold her there, will be pulled away from the shuttle


	Each particle – dust to golf ball to boulder size – is really a separate moon on its own orbit
	Orbit with Keplerian velocities: high in close, slow farther out
	Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up
	Structure in rings largely caused by gravity of moons


Like someone pushing kid on a swing
	Timing of pushes just as important as force used
		Pushing at random times has little effect
		Pushing at just right point in each cycle can produce big effect


	All within Roche limit
	Details controlled by Resonances and Shepard Satellites


	Four large moons (Io, Europa, Ganymede, Callisto)
	Regular (equatorial, circular) orbits
	Pattern of changing density and composition with distance
		Inner two (Io, Europa) mostly rocky
		Outer two (Ganymede, Callisto) more icy


	Io most volcanically active body in solar system
	Europa shows new icy surface with few craters


	Large tides from Jupiter flex satellites
	Friction from flexing heats interiors
	Important for Io, Europa, some other outer solar system satellites


	Tidal heating may keep H₂O liquid under ice cover

	Perhaps a location where life could evolve

	“Europa Orbiter” Mission being planned to determine if ocean exists


	Largest moon of Saturn
	Has thick atmosphere
		Pressure ~ 1 earth atmosphere
		Mostly N₂, some CH₄
		Gas held because of low T
	UV acting on CH₄ Þ smog
		Ethane produced – Lakes?
		Can “see” surface only in IR
	Cassini will drop probe in Fall 2004
	“Code of the Lifemaker” by James P. Hogan, good sf


	Largest moon of Neptune
	In unusual retrograde orbit
		Probably captured after it formed
		Tides during capture may have caused heating
	Does have thin atmosphere
	Shows recent “activity”
		Not volcanic – rather volatile related
		Ices migrate with seasons
		“Geysers” caused by heated ices