chapter 11 the jovian planets - uf astronomyfreyes/classes/ast2003/fr_ch_11.pdfchapter 11 the jovian...

Chapter 11 The Jovian Planets

•The Jovian planets: Jupiter,

Saturn, Uranus and Neptune

• Using Venus transit it was possible to get a

good value of the AU (1639). Knowing the

AU, it is possible to calculate the size of the

planets. Their physical size can be

calculated using their angular size and the

distance

Physical size = angular size x (2 π x distance)/360 (Read textbook page 30)

Once the distances have been determined it is possible to calculate the orbital radius of the

satellites. The mass of the planets can be calculated by measuring the orbital radius and the

orbital period of the satellites (and using Newton’s modified 3rd Kepler law)

Knowing the mass and diameter, allows to calculate the densities, proving that the Jovian

planets are very different from the terrestrial planets

The

Jovian

Planets

•The Jovian planets: Jupiter,

Saturn, Uranus and Neptune

•Their masses are large compared with

terrestrial planets, from 17 to 320 times

the Earth’s mass

•They are gaseous

•Low density

•All of them have rings

•All have many satellites

•All that we see of these planets are the

top of the clouds

•No solid surface is visible

•The density increases toward the

interior of the planet

•All of them located a larger distances

from the Sun, beyond the orbit of Mars

Jupiter •Named after the most powerful Roman

god

• It is the third-brightest object in the

night sky (after the Moon and Venus)

•It is the largest of the planets

•Atmospheric cloud bands - different

than terrestrial planets

•The image shows the Great Red spot, a

feature that has been present since it

was first seen with a telescope more

than 350 years ago

•Many satellites , about 66.

•The four largest are called Galilean

satellites. Discovered by Galileo in

1610

•A faint system of rings. Too faint to

see them with ground -based telescopes

Distance from Sun: 5.2 AU

Diameter: 11 diameter of Earth

Mass: 318 mass of Earth

Density: 1,3 g/cm^3

Escape velocity: 60 m/s

Surface temperature: 120 K

Composition: mostly H and He

Saturn • The second largest planet

•Visible with the naked eye

•Named after the father of Jupiter

• Almost twice Jupiter’s distance from

the Sun

• Similar banded atmosphere

• Uniform butterscotch hue

• Many satellites. The largest is Titan,

the only satellite to have a permanent

atmosphere

• Spectacular ring system seen with

even small telescopes

•This was the last planet know to the

ancients


Diameter: 9.5 Earth diameter

Mass: 95 Earth mass

Density: 0.71 g/cm^3

Escape velocity: 36 km/s


Composition: mostly H and He

Uranus

• Discovered by William Herschel in

1781

• Named after the father of Saturn

• Barely visible to naked eye, even

under dark skies

• Featureless atmosphere

•Green, bluish color due to presence of

methane in the atmosphere

•Methane absorb the red part of the

spectrum and reflect the blue

• It showed small deviations in the

expected orbit.

•Was another planet influencing its

motion?

• The deviation led to the discovery of

Neptune

•Faint ring system not visible with

ground-based telescopes



Mass: 14 mass of Earth


Escape velocity: 21 m/s


Composition: H compounds, H,

He, rocks

Neptune

• This is the other planet whose

gravitational pull is influencing the orbit

of Uranus

• It’s mass and orbit were determined

first , in 1845 by the English John

Adams and a bit later by the French

astronomer Urbain Leverrier

• In 1846 it was discovered by the

German astronomer Johann Galle

• Too faint, cannot be seen with naked

eye

• It has a bluish color due to the

presence of methane in the atmosphere

•Faint ring system, not visible with

ground-based telescopes



Mass: 17 Earth mass


Escape velocity: 24 km/s


Spacecraft Exploration of Jovian Planets •Pioneer 10 and 11. Reached Jupiter around 1973

•Voyager 1and 2 left Earth in 1977

•Reached Jupiter in March and July of 1979

• Used Jupiter’s strong gravity to send them on to Saturn - gravity assist

• Voyager 2 used Saturn’s gravity to propel it to Uranus and then on to Neptune

• Studied planetary magnetic fields and analyzed multi-wavelength radiation

• Both are now headed out into interstellar space!

Space Craft Exploration of Jovian

Planets, more recent missions

• Galileo - launched in 1989 and reached

Jupiter in December 1995

• Gravity assists from Venus and Earth

• Spacecraft has two components:

atmospheric probe and orbiter

• Probe descended into Jupiter’s atmosphere

• Orbiter entered orbit, went through moon

system

•Juno mission: On it way to Jupiter.

Scheduled to arrive at Jupiter in July 2016

• Cassini mission to Saturn arrived June 30, 2004

• It consist of the orbiter and the Huygens probe

•Orbiter will orbit Saturn and its moons for 4 years (at the present it

is active and returning data)

• Huygens probe launched from the orbiter. Descended on Titan

January 14, 2005 to study Saturn’s moon .

The mass-radius dependence for a H and He

planet

Notice that

Jupiter is

slightly larger

than Saturn even

if it is about 3

times more

massive

Adding more

mass, compress

the planet

increasing its

density but not

its size

Distortion of Jovian planets due to fast

rotation

Rapid rotation creates

a bulge around the

equator.

The shape departs

from a perfect sphere

•Saturn is distorted,

10% larger at equator

•Jupiter shape is also

distorted, about 7%

larger at equator.

Caused by fast

rotation, large radius

Jupiter’s Interior

(And Earth for comparison)

• Metallic hydrogen is a

superconductor. A

superconductor conduct

electricity with minimum or

no resistance

Jovian planets interiors

There is no data on direct measurements of the interior of the Jovian

planets

The structure of the interior of the Jovian planets is obtained through

modeling based on the composition and the mass

Jupiter’s Atmosphere Characterized by two main features: Colored bands

(zones and belts) and the Great Red Spot

Atmospheric content:

• molecular hydrogen – 86%

• helium – 14%

• small amounts of methane, ammonia, and water vapor

•The Great Red Spot seems to be a hurricane that has

lasted for more than 350 years

•The bands are caused by convections and high wind

velocity at the top of the clouds

•Darker belts lie atop downward moving convective

cells

•Lighter zones are above upward moving cells

•Belts are low-pressure, zones are high pressure

•Jupiter’s rapid rotation causes wind patterns to move

East/West along equator

•The color of the bands may be due to the presence of

trace elements sulfur and phosphorus and compounds

of molecules of these elements

•The formation of these molecules is sensitive to

temperature and that may account for the different

colors of Belts and Zones

Weather on Jupiter

Main weather feature : Great Red Spot!

• Swirling hurricane winds

• Has lasted for more than 350 years!

• Diameter twice that of Earth

• Rotates with planet’s interior

• The spot appears to be confined and

powered by the zonal flow. Not much

change in the latitude of the Great Red

Spot

Smaller storms look like white ovals (this one is over 40 years old)

Why do the storms last so long? On Earth, hurricanes loose power when then come upon land

No solid surface on Jupiter, just gas. Nothing to stop them once they start

Temperature profile of Jovian planets

Jovian planets - The axis tilt and magnetic fields

•All Jovian planets (and the Earth) have strong magnetic fields . They are caused by

the rapid rotation and liquid conductive cores or mantles.

•All of them emit low frequency radio emission. The emission is caused by the

interaction of electrons with the magnetic field

•The magnetic fields are offset from the center and have different tilt respect to the

rotational axis

•Uranus has the most inclined rotational axis: It has extreme seasons!

Jupiter’s Magnetosphere

Auroral emission

Jupiter magnetic field and the low frequency emission Jupiter has the strongest magnetic field of all the planets

•Jupiter produces strong radio

emission at short wavelength

or low frequencies (Less than

39 MHz)

•The radio emission is

generated by electrons

accelerated in the magnetic

field lines connecting Io and

the Jupiter

•This radio emission can be

received with a simple antenna

•Two types of radio emission

are common: L (long) bursts

and S (Short) bursts

Jovian Magnetospheres •All the Jovian planets have relatively

strong magnetic fields

•All emit low frequency radio emission

•Jupiter has the strongest magnetic

field

• Jupiter emit low and high frequency

emission (two different mechanisms)

• The cutoff of Jupiter low frequency

radio emission is around 40 MHz, the

highest frequency of all the planets.

•It is the only planet from which we

can receive the low frequency emission

in ground-based radio telescopes

•The rest of the Jovian planets emit

low radio emission but it cannot be

received in ground-based radio

telescopes. The frequency is too low

and cannot propagate through the

terrestrial ionosphere

Weather on Saturn

•Computer enhanced image shows bands, oval storm systems, and turbulent

flow patterns like those seen on Jupiter

•The colors in the image are not the natural colors of Saturn

The Atmospheres of Uranus and Neptune The atmospheric content:

•molecular hydrogen 84%

•helium 14%

•methane 2% (Uranus) 3% (Neptune)

Abundance of methane gives these planets their blue color Methane absorbs longer wavelength light (red) and reflects short

wavelength light (blue)

Uranus and Neptune bluish color and presence of methane in

their atmospheres

Weather on Uranus and Neptune

Uranus •Few clouds in the cold upper atmosphere – featureless

•Upper layer of haze blocks out the lower, warmer clouds

Neptune •Upper atmosphere is slightly warmer

than Uranus (despite its further distance

from Sun)

•More visible features (thinner haze, less

dense clouds lie higher)

•Storms – Great Dark Spot

•Seen in 1989 (Images taken by Voyager

spacecraft) – gone in 1996 (Hubble

telescope)

A Summary of the Jovian Planet Properties

•Most of their mass is Hydrogen and Helium – light elements = low densities

•High surface gravity allows their atmospheres to retain these light elements

•Dense compact core at the center

•No SOLID surface –The gaseous atmosphere becomes denser (eventually liquid) at

core

•Differential Rotation – outer regions rotate at a different rate than the inner regions

The moons or satellites of the Jovian planets

Jovian Planet Moons

Four largest Jupiter moons - Galilean Moons

•Jupiter - 67 moons

•Saturn - 62 moons

•Uranus - 27 moons

•Neptune - 13 moons

Jupiter’s Galilean satellites:

•Io - Jupiter’s moon with active

volcanoes!

•Europa - Jupiter’s moon covered

with frozen water - possible an

ocean of liquid water beneath

•Ganymede and Callisto - similar

in size to our moon, a bit larger.

•Ganymede is the largest moon in

the solar system

•There are:

•Six large moons, similar in size to our Moon

•12 medium-sized - 400 to 1500km

•Many small moons

Medium &

large moons

• All these moons have

enough self-gravity to be

spherical

• Some are now or were in

the past geologically active.

• Most of them have

substantial amounts of ice.

Jupiter

Saturn

Uranus

Neptune

Jupiter’s “Galilean Moons”

An Unusual Family

Io Europa Ganymede Callisto

Moon

• Io has several active volcanoes.

• Europa may have an ocean of liquid water under

its ice.

• Ganymede & Callisto may also have sub-surface

oceans?

How can we account for the unusual

features?

Shouldn’t they be cold & dead?

What makes Jupiter’s Galilean moons unusual?

Io’s Volcanoes • So far about 80 active

volcanoes have been identified using data mainly from Voyager and Galileo spacecrafts

• Volcanic eruptions mainly composed of sulfur & sulfur dioxide

• Volcanic plumes about 150 km high and 300 km wide

• Variety of volcanic hot spots

• Large lava lakes made of liquid sulfur

• Tidal heating provides the source of volcanic activity.

• Io orbit is elliptical. Compressing and stretching of Io release heat.

Io: Two images separated by 15 years

A better view of Io’s volcanoes

Tidal Heating

Io is squished and stretched as it orbits

Jupiter . This releases of heat and rises

the internal temperature

Why is its orbit so

elliptical?

The Jovian Moons Orbital resonance between the orbital periods of Io,

Europa and Ganymede The 3 closest moons line up every 7 Earth days (resonance)

Tugging in the same direction distorts the orbit from a circle to an ellipse

1 orbit of Ganymede = 2 orbits of Europa = 4 orbits of Io

Smooth Europa

• Icy surface covering a

large rocky core:

– Surface is very smooth &

young.

– Fractured into ice rafts &

floes a few kilometers

across,

– Repaved by water or

geysers through the cracks

in the ice.

Europa

• Surface is ice covered

• Extensive & complex network

of cracks in icy crust

– internal geologic activity

Europa (200km square)

Europa

• Salt water oceans below thick layer of ice?

(Calculations show it may have twice as

much water as Earth!!)

• Mostly salt water, some magnesium

sulfate, sulfurs (red color)

Does Europa have liquid water?

What lies beneath Europa’s

surface?

One possibility:

– 100-200 km of convective ice

above a rocky core

The most probably scenario

based on measurement of

Europa’s magnetic field:

– Thin ice crust a few km thick

over a 100 km deep water

ocean.

Europa How Europa can maintain liquid water?

•Heat in the interior come from interaction

(tidal heating) with Jupiter and distortion

of the orbit (elliptical) by interaction with

nearby satellites

•Thermal vents may bring the heat from

the core.

•Heat may keep the interior temperature

above freezing point

Possibility of life?

• The existence of liquid water does not

imply the emergence of life. The salty

water is a hostile environment. But we

have seen on Earth that life can be present

in environment that were considered

hostile

Tidal stresses crack Europa’s surface ice. Similar to

icebergs, large chunks of ice that have been broken and

reassembled

•Titan, Saturn largest satellite Titan is the only satellite in the solar system to

have an atmosphere. It has a methane-ammonia

atmosphere

It was recently visited by Cassini (at the present in

orbit around the planet) and the Huygens probe.

Rocky surface and evidence of erosion by

liquid/slush.

Titan

•Properties:

– Mass: ~0.02 Earth-mass

– Radius: 0.4 REarth

– Density: ~1.9 g/cm^3

– Icy mantle over a rocky core.

• This is the only satellite (moon) in the solar system that has heavy atmosphere

Titan’s Atmosphere •Composition:

– ~80% N2 (nitrogen)

– ~3% CH4 (methane)

– Argon

– Hydrocarbons like:

• Ethane = C2H6

• Acetylene = C2H2

• Ethylene = C2H6

• Propane = C3H8

– Clouds of methane & N2 ices

The Huygens probe The Huygens lander was carried by

the Cassini spacecraft mission .

The image to the right is an image

from the surface of Titan returned by

the Huygens probe

The methane/ethane lakes in Titan.

Radar images taken by Cassini

Lakes on Titan (radar maps)

Titan’s Liquid Lakes

Cassini radar have been

able to image several

smooth regions that have

been identified as lakes of

liquid methane/ethane

Titan, a reflection of sunlight in a methane/ethane

lake.

(Image taken by Cassini spacecraft)

Titan interior

Saturn satellite Mimas and Star

Wars’ Death Star

Triton

Triton - Neptune’s large

moon

•It has a retrograde orbit . It orbit in

direction opposite to Neptune

rotation

•Voyager 2 detected geysers of

nitrogen gas rising several km high

• The gas jets of nitrogen comes

from liquid nitrogen heated by some

internal source of heat

•A very thin atmosphere of nitrogen

•Temperature about 37 K

The Jovian Planets rings

Rings

All of the Jovian planets

have rings

The most spectacular are

Saturn’s rings

•They are very thin, less

than a few km

•Rings are not solid objects

• They are comprised of

many small solid particles

•All the particles are in

orbit around the planet

•Water ice is the primary

constituent

Why do rings form? Tidal forces (differential gravitational

forces) of the large planet can break apart

a close enough moon.

Rings

• Rings consist of billions of

small particles or moonlets

orbiting close to their planet

– size of particle ranges from

grain of sand to house-

sized boulders

Rings

• Particles follow Kepler’s laws

– inner particles revolve faster than

those farther out

– ring are not rotating, rather

individual moonlets revolving

• if ring particles widely spaced -

move independently

• if particles are close -

gravitationally interact

• moons clear gaps in rings

Saturn’s ring in false colors to enhance the

composition

Saturn rings, gaps and shepherding moons

Origin of Rings

• Breakup of shattered satellite

• Remains of particles that were unable to come together and form satellite

• Gravity plays important role

– differential force of gravity -- tidal forces

• tear bodies apart

• inhibit loose particles from coming together

DFg DFg

DFg

Roche Limit

• Roche Limit - the closest distance an object can come to another object without being pulled apart by tidal forces

Comparing Jovian Ring Systems

• Compared to Saturn, the ring

system of other Jovian planets:

• have fewer particles

• are smaller in extent

• have darker particles

• The rings of Uranus were

discovered in 1977 when the planet

passed in front of a star and the

rings dimmed the light from the star

• The rings of Jupiter and Neptune

were discovered by the Voyager

spacecrafts

• Other unsolved mysteries:

• Uranus’ rings are eccentric and

slightly tilted from its

equatorial plane.

• Neptune has partial rings.

Jovian Rings

An example: Comet Shoemaker-Levy 9. It broke into 23 pieces after coming inside the Roche limit of

Jupiter in 1993

Collided with Jupiter in July 1994

Comet S-L 9 The string of pieces of the comet on their way to

Jupiter

chapter 11 the jovian planets - uf astronomyfreyes/classes/ast2003/fr_ch_11.pdfchapter 11 the jovian...

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