Introduction to Solar System 4

7/28/2019 Introduction to Solar System 4

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18-Apr-13

IESO

Introduction to Solar System

Part 4


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Comparative Planetology

of the Jovian Planets


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A Travel Guide to the Outer Planets

Hydrogen-rich atmospheres

Large satellite systems


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Atmospheres

Hydrogen rich

Filled with clouds

On Jupiter and Saturn, the clouds form Stripes and

bandsbelt-zone circulation. The atmospheres are not deep relative to the size of the

planet.


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Interiors

Low densities and flattened shapes indicate Jovianplanets cant be solid like the Terrestrial planets.

Below the atmosphere, Jupiter and Saturn are mostly

liquid hydrogen. The very center of the worlds are

solid cores of dense material, rock and metal. The interiors of Uranus and Neptune are mostly water

in the form of liquid and ice. They also have dense

material in their cores.


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Satellite Systems

All of the Jovian worlds have large satellite

systems.

The moons interact gravitationally with each other and

the ring systems.

Some of the moons are currently or have beengeologically active.

Regular moons

Formed where they are at the same time as the planet formed

Irregular moons Captured


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Jupiter

Largest and mostmassive planet in the

solar system:

Contains almost 71% ofall planetary matter in the

solar system.

Most strikingfeatures visible from

Earth: Multi-colored

cloud belts

Visual image

Infrared false-

color image


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Jupiter Statistics

Average distance from the sun 5.20 AU Orbital period 11.9 years

Period of rotation 9.92 hours

Mass 318 x Earth

Exploration of Jupiter

Voyager 1 flyby March, 1979

Voyager 2 flyby July, 1979

Galileo, 1995

New Horizons flyby, 2007


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Jupiter emits ~ twice as much energy as it absorbs

from the sun. This is heat left over from the contraction of the planet.

This energy is in the infrared.


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Jupiters Interior

From radius and massAverage density of Jupiter 1.34 g/cm3

=> Jupiter can not be made mostly of rock, like earthlike planets.

Jupiter consists mostly of hydrogen and helium.

Due to the high pressure,

hydrogen is compressed into a

liquid, and even metallic state.

T ~ 30,000 K


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There is no distinct boundary between Jupiters atmosphere and itsliquid hydrogen layer like there is a distinct boundary between Earthsatmosphere and oceans. The hydrogen just keeps getting denser thedeeper within the planet.

10% of the way from the surface to the center of Jupiter, the liquidhydrogen is under so much pressure that it becomes liquid metallichydrogen.

Metallic hydrogen results when hydrogen is compressed to the point thatit becomes ionized and degenerate. The electrons are unbound and behavelike the conduction electrons in a metal.

This is a good conductor of electricity. The liquid metallic hydrogen inJupiter is stirred by convection currents and spun by Jupiters rotation.This creates a dynamo effect like in the sun and in Earths liquid core.Therefore, Jupiter has a magnetic field, which is 10 times stronger thanEarths.


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Aurorae on Jupiter

Just like on Earth,

Jupiters

magnetosphere

produces aurorae

concentrated inrings around the

magnetic poles.

~ 1000 timesmore powerful

than aurorae on

Earth.


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Jupiters Magnetic FieldDiscovered through observations of decimeter (radio) radiation

Magnetic field at least10 times stronger than

Earths magnetic field.

Magnetosphere over

100 times larger than

Earths

magnetosphere.

Extremely intense

radiation belts:

Very high energyparticles can be

trapped; radiation

doses corresponding

to ~ 4000 times lethal

doses for humans!


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Jupiters Atmosphere

Jupiter has a very thin hydrogen and

helium atmosphere above the cloudlayers.

The transition to liquid hydrogen zone

~ 1000 km below clouds.

The Galileo probe entered Jupitersatmosphere in 1995. It parachuted

through the upper atmosphere of

clear hydrogen, released its heat

shield, then descended until it was

crushed.


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All of the cloud compounds are white. The color in the clouds comes from other molecules

formed from reactions caused by lightning or sunlight.

Three layers

of clouds:

1. Ammonia(NH3)

crystals

2. Ammonia

hydrosulfide

(NH4SH)

3. Water

crystals


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The Cloud Belts of JupiterDark belts and bright zones.

Zones higher and cooler than belts;high-pressure regions of rising gas.


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The Cloud Belts on Jupiter (II)

Just like on Earth, high-and low-pressure zones

are bounded by high-pressure winds.

Jupiters cloud belt structure has remained

unchanged since humans began mapping them.


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On both Earth and Jupiter, winds circulate

clockwise around the high-pressure areas in thenorthern hemisphere and counter clockwise south

of the equator.


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The three white ovals here arecounterclockwise, high-pressure weather

systems that were visible in Jupiterssouthern hemisphere since they formed inthe 1930s. They merged in 1998 and the

pear shaped circulation in between thestorms vanished. In 2006, the stormintensified and turned red (Red Jr.).


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Comet Impact on Jupiter

Impacts released energies equivalent to a fewmegatons of TNT (Hiroshima bomb: ~ 0.15 megaton)!

Visual: Impacts

seen for many daysas dark s ots

Impact of 21

fragments of

comet

Shoemaker-

Levy 9 in 1994

Impacts

occurred

just behind

the horizon

as seen

from Earth,

but came

into viewabout 15

min. later.

Impact sitesappeared

very bright in

the infrared.


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Jupiters Family of MoonsOver 60 moons known now; new ones

are still being discovered.

Four largest moons were discovered by Galileo:

The Galilean moons

Io Europa Ganymede Callisto

Interesting and diverse individual geologies.


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Callisto: The Ancient FaceTidally locked to Jupiter, like all of Jupiters moons.

Av. density: 1.8 g/cm3

composition: mixture

of ice and rocks

Dark surface, heavily

pocked with craters.

No magnetic field.

Layer of liquid water, ~ 10 km thick, ~ 100 km below

surface, probably heated by radioactive decay.


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GanymedeLargest of the 4 Galilean moons. Av. density = 1.9 g/cm3

Rocky core Ice-rich mantle

Crust of ice

1/3 of surface old, dark, cratered;

rest: bright, young, grooved terrain


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Ganymede is the largest moon in the solar system.

It is larger than Mercury.

It also has a layer of liquid water under the

surface.


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Europa: A Hidden Ocean

Av. density: 3 g/cm3

composition: mostly

rock and metal; icy surface.

Close to Jupiter should be

hit by many meteoroid impacts;

but few craters visible.

Active surface; impact

craters rapidly erased.


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Like icebergs on an arctic ocean, blocks of crust on Europa appear to have

floated apart and rotated. The blue icy surface is stained brown by mineral-rich

water venting from below the crust. White areas are ejecta from the impact that

formed Pwyll crater.


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The Interior of Europa

Europa is too small to retain its internal heat

Heating mostly from tidal interaction with Jupiter.

Core not molten

No magnetic field.

Europa has a liquid

water ocean below the

icy surface about 200

km thick.


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Io: Bursting Energy

Most active of all Galilean moons; no impact craters visible at all.

Over 100 active

volcanoes!

Av. density = 3.6 g/cm3

metallic core

rocky mantle

low-density crust

Activity powered by

tidal interactions

with Jupiter.


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Jupiters RingNot only Saturn, but all four

Jovian Planets have rings.

Jupiters ring: dark and

reddish; only discovered by

Voyager 1 spacecraft.

Galileo spacecraft

image of Jupitersring, illuminated

from behind

Composed of microscopic

particles of rocky material

Location: Inside Roche limit, where

particles cant pull themselves

together to form moons.

Ring material cant be old because

radiation pressure and Jupiters

magnetic field force dust particles

to spiral down into the planet.Rings must be constantlyre-supplied with new dust.


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Small moons that orbit near the outer edge of the rings losedust particles because of micrometeorite impacts.

Observations show that the main ring is densest at its outer edgewhere a small moon orbits.

The gossamer rings are fainter but extend out farther than themain ring. They are densest around the orbits of 2 small moons.

As well as supplying material to the rings, these moons

may keep them from spreading outward. Shepherd moons.


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Formed from

cold gas in theouter solar

nebula, where

ices were able to

condense.

Rapid growth

Soon able to

trap gas directlythrough gravity

Heavy materials

sink to the center

In the interior,

hydrogen becomesmetallic (very good

electrical conductor)

Rapid rotation strong

magnetic field

Rapid rotation

and large size belt-zone

cloud pattern

Dust from meteorite impacts onto

inner moons trapped to form ring

The History of Jupiter


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Saturn Statistics

Average distance from the sun 9.54 AU

Orbital period 29.5 years


Mass 95 x Earth

Exploration of Saturn

Voyager 1 flyby, November 1980

Voyager 2 flyby, August 1981Cassini went into orbit around Saturn in 2004.

http://www.boston.com/bigpicture/2009/10/saturn_at_equinox.html


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From 20 degrees above the ring plane, Cassini's wide angle camera shot 75 exposures in succession for this

mosaic showing Saturn, its rings, and a few of its moons a day and a half after exact Saturn equinox, when

the sun's disk was exactly overhead at the planet's equator. The images were taken on Aug. 12, 2009, at adistance of approximately 847,000 km (526,000 mi) from Saturn. (NASA/JPL/Space Science Institute)


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The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the

Cassini Division in this natural color image taken as Saturn approaches its August 2009

equinox. Images taken using red, green and blue spectral filters were combined to create

this natural color view.

Saturn


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SaturnMass: ~ 1/3 of mass of Jupiter

Radius: ~ 16% smaller than Jupiter

Av. density: 0.69 g/cm3

Would float in water!

Must be mostly hydrogen

and helium.Only a small core of heavy

elements.

Rotates about as fast as Jupiter, but is twice as oblate mostly

liquid.


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Saturn has belt - zone circulation just like Jupiter,

but its harder to see because, the belts and zones

on Saturn are deeper in the atmosphere below alayer of methane haze.

This is because the layers of clouds form at the same temperatures in

the atmosphere as they form in Jupiters atmosphere, but since Saturn

is farther from the sun, these temperatures are deeper in Saturnsatmosphere.


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Saturns Atmosphere

Three-layeredcloud structure,

just like on

Jupiter

Much stronger

winds than onJupiter:

Winds up to ~ 500 m/s near the equator!


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Because the pressure is lower in Saturn than

Jupiter, it must have less liquid metallic hydrogen.

This explains why its magnetic field is 20 times

weaker.

Saturn also radiates more energy than it receives

from the sun like Jupiter.


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The Moons of Saturn

Saturn has ~ 50 moons. Most are small

All contain a mixture of ice and rock.

Some moons are probably captured asteroids.

Some moons, like Titan may have formed when Saturn

formed.


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Titan: Saturns Largest Moon

Thick atmosphere,

hiding the surface from

direct view.

About the size of

Jupiters moon

Ganymede.

Slightly larger than

Mercury.

Rocky core, but also

large amount of ice.


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Titans Atmosphere

Mostly nitrogen with traces of

argon and methaneBecause it is so cold, gas

molecules do not move fast

enough to escape.

Because of the thick, cloudy

atmosphere, surface features are

only visible in infrared images.

Clouds are formed by sunlight

reacting with methane to produce

organic particles.The surface is rich in methane ice.

Liquid methane and ethane may

form lakes.


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The organic material in the clouds could fall to the

surface and into the lakes. (An organic

compound is any member of a large class of

Chemical compounds whose molecules contain

carbon.)

However, it is very cold180 degrees C. So itsunlikely anything could live there.

Titan is cooled by an inverse greenhouse effect. The

atmosphere blocks sunlight, but lets infrared radiation

escape.


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The Cassini probe Huygens photographed dark drainage channelsliquid

methane falls as rain and flows into lowlands.

Infrared images of Titan suggest the presence of

methane volcanoes.

Saturns Smaller Moons


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Saturn s Smaller Moons

Saturns smaller moons formed of rock and ice;

heavily cratered and most appear to be

geologically dead.

Tethys:Heavily cratered;

marked by 3 km

deep, 1500 km

long crack.

Iapetus:Leading (upper right)

side darker than rest

of surface because of

dark deposits.

Enceladus:Active; regions with fewer

craters, containing

parallel grooves, possibly

filled with frozen water.


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Enceladus is venting

water, ice and organic

molecules from geyers

near its south pole.

Thermal infrared

image reveals internal

heat leaking intospace from the tiger

stripe cracks where

the geysers are

located.


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The Death Star Moon Mimas

S Ri

A Ring


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Saturns Rings

Ring consists of 3

main segments:A, B, and C Ring

g

B Ring

C Ring

separated by

empty regions:

divisions CassiniDivision

Rings cant have been

formed together with

Saturn because

material would have

been melted and blown

away by hot Saturn at

time of formation.

Rings must be

replenished by

fragments of

passing comets

/ meteoroids.


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The ring particles have compositions that resemble

the moon Phoebe. A large impact on Phoebe mayhave contributed much material to the rings.


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Composition of Saturns Rings

Rings are

composed of

ice particles

moving at large

velocities around

Saturn, but small

relative velocities(all moving in the

same direction).


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Saturns rings lie inside the planets Roche limit where thering particles cannot pull themselves together to form a

moon. There are moons amongst the rings of Saturn and Jupiter, Shepard

moons, but they probably formed elsewhere and were latercaptured by the large planets. They may eventually be pulled apart

by tidal forces.

The A and B ring contain particles that range in size fromabout the size of dust to the size a golf ball.

The C ring contains boulder size material. The particles inthe C ring are also less bright than those in the A and Bring because they contain less ice and more minerals.

Sh h d M


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Shepherd Moons

Some moons in

orbits close to the

rings focus the ring

material, keeping

the rings confined.

Di i i d R


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Divisions and Resonances

Moons do not only serve as shepherds.

Where the orbital period of a moon is a small-number

fractional multiple (e.g., 2:3) of the orbital period of material

in the ring (resonance), the material is cleared out

Divisions


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The History of Saturn

Saturn formed in the outer solar system where ice particleswere stable.

It grew rapidly and became massive enough to attracthydrogen and helium by gravitational collapse.

The heavier elements sank to the middle to form a core.

The hydrogen formed a liquid mantle containing liquidmetallic hydrogen - Magnetic field.

The rings were formed later by collisions between cometsand Saturns moons.

U


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Uranus

1/3 the diameterof Jupiter

1/20 the mass

of Jupiter

no liquid metallic

hydrogen

Deep hydrogen

+ helium

atmosphere


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Uranus Statistics

Average distance from the sun 19.2 AU

Orbital period 84 years


Mass 14.5 x Earth

Exploration of Uranus

Voyager 2 flyby 1986


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Circulation in an electrically conducting mantle

may generate the planets magnetic field.

Th At h f U


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The Atmosphere of UranusLike other Jovian Planets: No surface.

Gradual transition from gas phase to fluid interior.

Mostly H; 15% He, a few %

methane, ammonia and

water vapor.

Voyager image

combined with HST

image:

Blue color due to

methane, absorbing

longer wavelengths

Cloud structures only visible after artificial computer enhancement

of optical images taken from Voyager spacecraft.


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Cloud Structures

of Uranus

Hubble Space

Telescope image ofUranus shows cloud

structures not present

during Voyagers

passage in 1986.

Possibly due to

seasonal changes of

the cloud structures.


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At the temperatures and pressures present in Uranus and

Neptune, methane can decompose and release carbon.

The carbon can form diamonds the size of pebbles. On Uranus and Neptune it may be raining diamonds.

This in falling material may heat the interior.


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h f


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The Moons of Uranus

5 largest moons visible from Earth.

10 more discovered by Voyager 2;

more are still being found.

Dark surfaces, probably ice darkened

by dust from meteorite impacts.

5 largest moons all

tidally locked to Uranus.

Ariel

Miranda


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Ariel has an old surface, butsome regions show valleysindicating there was activity inthe past.

Miranda has peculiar markingswhich may have formed wheninternal heating causedconvection in the ice of its

mantle.

The Rings of Uranus


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The Rings of UranusRings of Uranus and Neptune are similar to Jupiters rings.

Confined by shepherd moons; consist of dark material.

Rings of Uranus were

discovered through

occultations of a

background star

Apparent motion of

star behind Uranus

and rings


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When Voyager 2 looked back at the rings of Uranus illuminated from

behind by the sun, the rings were not bright. There is no forward

scattered light. Therefore, the rings must not be made of small

particles like Jupiters rings. They are made of particles a meter indiameter and larger.

The ring particles of Uranus are darker than lumps of coal. If the ring

particles are made of methane rich ices, radiation from the planet could

break the methane down to release carbon and darken the ices. This

same process may also darken Uranus moons.

The rings must be replenished by impacts or they would eventually

disappear.

Th Hi t f U


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The History of Uranus Since Uranus formed in the outer solar nebula where the material was

less dense, it must have formed slowly. While it did capture gas fromthe nebula, it didnt get massive enough to capture large amounts likeSaturn and Jupiter.

Uranus is rich in water and ice rather than hydrogen and helium.

Uranus and Neptune may have formed closer to the sun then they arenow, but interactions with Jupiter and Saturn moved them to their

current location. These same interactions may have tipped Uranus onits side.

While it was forming, it may have had a catastrophic impact with alarge planetesimal knocking it on its side.

Impacts between comets and its moons created the material to form

rings.

N t St ti ti


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Neptune Statistics

Average distance from the sun 30.1 AU Orbital period 164.8 years


Mass 17.2 x Earth

Explorations of NeptuneVoyager 2 flew past in 1989.

Neptune farthest from the sun


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Neptunefarthest from the sun

Discovered in

1846 at positionpredicted from

gravitational

disturbances on

Uranus orbit byJ. C. Adams and

U. J. Leverrier.

Blue color from

methane in theatmosphere

4 times Earths

diameter; 4 %

smaller than Uranus


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Uranus and Neptune both get their blue color fromMethane in their atmosphere. Neptune is bluer because ithas more methane:

Neptune 3%Uranus 2%

Methane absorbs red photons better than blue photons andscatters blue photons better than red.

Because Uranus has less methane, it has a more blue-greencolor.


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Coreheavy elements

Mantlewater, ices, and minerals

Atmospherehydrogen rich

The Atmosphere of Neptune


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p p

Cloud-belt structure with high-velocity winds; origin not well understood.

Darker cyclonic disturbances, similar to Great Red Spot on Jupiter,

but not long-lived.

White cloud features of methane ice crystals


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Neptunes atmosphere may have more activity

than Uranus because it has more heat flowing out

of its interior. The cold temperatures of Uranus and Neptune

may prevent the formation of molecules that give

the clouds of Jupiter and Saturn their colors.


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Neptune has a highly inclined magnetic field.

This indicates that there is circulation in the

interior. Ammonia dissolved in the liquid water conducts

electricity.

Convection in the water and the rotation of the planet

drive the dynamo effect.

The Rings of


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The Rings of

Neptune

Made of dark material,

visible in forward-

scattered light.

Interrupted between

denser segments (arcs)

Focused by small shepherd

moons embedded in the

ring structure.

Ring material must be

regularly re-supplied

by dust from meteorite

impacts on the moons.

The Moons of Neptune


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The Moons of NeptuneTwo moons (Triton and Nereid) visible from Earth;

6 more discovered by Voyager 2

Unusual orbits:

Triton: Only

satellite in the

solar system

orbiting clockwise,

i.e. backward.

Nereid: Highly

eccentric orbit;

very long orbital

period (359.4 d).

The Surface of Triton


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Triton can hold atenuous atmosphere of

nitrogen and some

methane; 105 times less

dense than Earths

atmosphere.

Very low temperature (34.5 K)

Surface composed of ices:

nitrogen, methane, carbon

monoxide, carbon dioxide.

Possibly cyclic nitrogen icedeposition and re-vaporizing on

Tritons south pole, similar to CO2

ice polar cap cycles on Mars.

Dark smudges on the nitrogen ice surface, probably due to methane rising

from below surface, forming carbon-rich deposits when exposed to sunlight.



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Ongoing surface activity:Surface features

probably not more than

100 million years old.

Large basins might have

been flooded multipletimes by liquids from the

interior.

Radioactive decay may

cause water-ammoniavolcanism.

Neptunes History


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Neptune s History

Grew slow, so it didnt capture large amounts of hydrogen andhelium via gravitational collapse.

Heat generated by radioactive decay and also possibly fromdiamond crystals falling inward.

The heat flowing outward could produce the magnetic field and

create atmospheric circulation. The moons orbits suggest a cataclysmic impact in the past.

Impacts on moons created debris that formed the rings.

What evidence is there of large impacts in the


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past in our Solar System?

1.

The high density of Mercury, suggesting its mantle was blastedaway

2. The backwards rotation of Venus

3. The existence of Earths moon

4. The lowlands on Mars5. Uranus rotates on its side

6. Neptunes moons odd orbits

7. Planetary ring systems

What Planets have we explored via


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spacecraft?

Introduction to Solar System 4

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