4.5JOVIAN PLANETS

THE OUTER PLANETS All larger than Terrestrial Planets with thick

atmospheres and very inhospitable. No solid surfaces

Mostly Hydrogen and Helium

Strong atmospheric circulation (winds/storms)

Ring systems

Multiple moons (Regular vs. Irregular satellites)

JUPITER Largest and most

massive planet of the solar system.

Contains almost ¾ of all planetary matter within the solar system.

Mostly liquid Hydrogen.

Most striking features visible from Earth Multi-colored cloud belts; Great Red Spot

JUPITER Explored in detail by

several space probes:

Pioneer 10

Pioneer 11

Voyager 1

Voyager 2

Cassini

Galileo

VOYAGER 1Video data from approach to Jupiter in 1979

MASS OF JUPITER Can be inferred from the radius and orbital period

of Io, the innermost of the 4 Galilean moons.

Using NVK3L MJupiter = 318 MEarth

CHEMICAL COMPOSITIONJUPITER VS. SATURN

JUPITER’S INTERIOR Average density ~ 1.34 g/cm3

Therefore, cannot be made of mostly rock like Earth-like planets. Rock has a density of 2.5 4 g/cm3.

JUPITER’S ROTATION Most rapidly

rotating planet in the solar system.

Rotation ~ 9.92 h

Revolution ~ 11.87 y

Appears slightly flattened and is 6% larger in diameter through equator than through its poles; referred to as oblateness.

JUPITER’S MAGNETIC FIELD

Discovered through observations of decimeter (radio) observations.

Created by the liquid metallic Hydrogen interior. Good electrical conductor.

Believed to be 10 times stronger than Earth’s. Very intense radiation belts.

Extremely high-energy particles can be trapped radiation doses corresponding to 100 times lethal doses for humans!

JUPITER’S MAGNETIC FIELD Just like on Earth,

Jupiter’s magnetosphere produces aurora concentrated in the rings around the magnetic poles.

1000 times more powerful than the aurora on Earth.

JUPITER’S ATMOSPHERE Liquid Hydrogen ocean has

no surface.

Pressure and temperature higher than the critical point for Hydrogen, meaning there is no difference between gaseous and liquid Hydrogen.

Very thin atmosphere above cloud layers.

Cold outer layers; interior layers warm but pressure is immense.

Transition to liquid Hydrogen zone ~ 1000 km below clouds.

JUPITER’S ATMOSPHERE

JUPITER’S CLOUD BELTS On Earth, the temperature

difference b/w poles and equator drives a wave-shaped wind organizing high and low pressure areas.

On Jupiter, the poles and equator have about the same temperature; no wave-shaped winds but rather bands called belts and zones.

JUPITER’S CLOUD BELTSDARK BELTS

Lower AltitudeWarmer Temperatures

LIGHT ZONESHigher Altitude

Cooler Temperatures

THE GREAT RED SPOT Several bright and dark spots

mixed in with cloud structure. Cyclones/Anticyclones

Largest and most prominent: Great Red Spot. Visible for over 300 years.

Formed by rising gas carrying heat from below the clouds, creating a vast, rotating storm.

For the first time, very recently, a new similar red storm system has been observed, Red Jr.

JUPITER’S RINGS Discovered in 1979 by Voyager 1.

Dark and reddish in color; rocky rather than icy (mostly microscopic particles).

Orbit inside the Roche Limit, the distance from a planet within which a moon cannot hold itself together by its own gravity. International Space Station can orbit

inside Earth’s Roche Limit; held together by bolts and welds.

Can’t be old pressure of sunlight and Jupiter’s extensive magnetic field cause ring particles to spiral into cloud layers of Jupiter. Frequently replenished.

Fainter rings known as gossamer rings, extend twice as far from Jupiter than the main ring.

HISTORY OF JUPITER Formed from cold gas in the

solar nebula, where ice particles could condense.

Rapid growth.

In the interior, Hydrogen becomes metallic due to pressure (good electrical conductor). Rapid rotation strong

magnetic field.

Heavy materials sink to center.

Dust from meteorite impacts onto inner moons trapped to form rings.

JUPITER“King of Gods”

JUPITER’S FAMILY OF MOONS Has 63 known moons; new ones still

being discovered.

4 largest moons discovered by Galileo (Galilean Moons):

IO EUROPA GANYMEDE CALLISTO

IO: ROARING VOLCANOES Innermost and

most active of all Galilean moons.

No impact craters visible.

Hundreds of active volcanoes.

Activity powered by tidal interactions with Jupiter.

Average density ~ 3.55 g/cm3

Mostly rock.

EUROPA: HIDDEN OCEAN Almost completely free of

impact craters. Active surface erases

craters almost as fast as they form.

Bright face tells you surface is young.

Albedo of 0.69, meaning it reflects 69% of the light hitting its surface.

SURFACE OF EUROPA

Long cracks in the icy crust and sections moving apart as if they were icebergs floating on water provide further evidence for tectonic activity.

INTERIOR OF EUROPA Too small to retain internal heat.

Heating comes from tidal interactions with Jupiter.Core not molten No magnetic field.

Europa has a liquid water ocean ~ 15 km below the icy surface.

GANYMEDE: A HIDDEN PAST

Largest moon in the solar system; larger than Mercury itself. Average density ~ 1.9 g/cm3.

Underwent differentiation. Rocky core, ice-rich mantle, crust

of ice 500 km thick.

Bright, parallel grooves across the surface indicate an active past.

Surface once flooded.

Experiences 2 unusual processes due to its size and closeness to Jupiter:

Tidal Heating Inward Focusing of Meteorites

CALLISTO: THE ANCIENT FACE

Average density ~ 1.8 g/cm3

Mixture of ice and rocks.

Old, dark surface heavily cratered.

Measurements show it never fully differentiated to form a dense core and lower-density mantle.

Interaction with Jupiter’s magnetic field suggests is has a layer of liquid water. Heat from interior

through slow radioactive decay.

Impact scar shown above is one of the largest in the solar system (4000 km ~ 2500 mi).

THE GALILEAN MOONS Minor moons are believed to be captured asteroids.

Galilean moons probably formed with Jupiter. Formed from a disk of material surrounding Jupiter (mini “solar nebula”).

Earliest moons may have spiraled into Jupiter.

Galilean moons are probably a 2nd generation of moons for Jupiter.

SATURN Average density ~ 0.69 g/cm3

Less dense than water (1.0 g/cm3) Would float on water!

Rotation ~10.66 h

Revolution ~ 29.46 y

SATURN’S ATMOSPHERE Hydrogen and Helium rich

with heavy element core. Displays belt-zone

circulation, similar patterns to Jupiter (not as distinct).

Actually exhibits faster wind speeds, but fewer wind zones.

Much colder atmosphere than Jupiter’s (twice as far from the Sun, receives only ¼ as much solar energy per square meter).

SATURN’S RINGS An astronomer once

said: “ The rings are made of

beautiful physics.”

In 1609, Galileo became the first to see the rings, but didn’t recognize them as individual rings.Drew Saturn as a central

body with two smaller bodies surrounding it.

SATURN’S RINGS Consists of 3 main segments: A, B, and C

Separated by empty regions called divisions (Cassini A /B; Encke A) Rings replenished by passing comets and meteoroids.

Just as with Jupiter, Saturn’s rings lie inside Roche Limit.

Some smaller moons, known as shepherd moons, orbit close to the rings and keep the ring material confined.

SATURN’S RINGS Made of billions of ice

particles (microscopic specks chunks larger than a house). Voyager 1

Voyager 2

Cassini

Rings could not have formed when Saturn formed once hot and ring material would have vaporized.

SATURN’S MOON - TITAN 2nd largest moon in the solar

system.

Rocky core; abundant ice.

Only natural satellite with an atmosphere; thick hides the surface.

SATURN’S MOON - TITAN Explored extensively by Cassini

spacecraft, which released the Huygens probe. Landed on surface of Titan in

2005 and radioed back images.

Few craters suggests geologic activity?

Most of its atmosphere is Nitrogen; smaller amounts of methane. Sunlight converts methane (CH4)

into the gas ethane (C2H6) plus a collection of other organic molecules.

Produces smog-like haze settles into goo.

Methane/ethane rain?

SATURN’S SMALLER MOONS

HISTORY OF SATURN Most of Saturn’s story

parallels Jupiter’s.

Smaller with less liquid metallic Hydrogen, thus producing a weaker magnetic field.

Rings are not primordial, meaning the material in them now has not been in its current form since the formation of the planet. Permanent or temporary?

SATURN“God of Harvest”

URANUS Chance discovery made by

William Herschel in 1781 while scanning the sky for nearby objects with measurable parallax.

Until that time, astronomers only knew of five planets aside from Earth.

“Luck is what happens to the people who work hard.”

MOTION OF URANUS Just over 19 AU’s from the Sun.

Rotation ~ 17.23 h

Revolution ~ 84.0 y

Rotation axis inclined 97.9° from the perpendicular to its orbit (tilted on its side retrograde rotation). Impact during planetary

development?

Extreme seasons.

Rotation between eternal sunlight and extreme darkness for many years.

First good photographs taken in 1986 as Voyager 2 flew past.

19.18 AU97.9

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ATMOSPHERE OF URANUS Like Jupiter and Saturn, no surface exists on Uranus.

Mostly Hydrogen, with 15% Helium, and about 2% methane, ammonia, and water vapor.

Gradual transition from gas (molecular) state to fluid-like interior.

Blue-green color comes from methane good absorber of longer wavelength photons. Cloud structures visible after computer enhancements form

optical images.

ATMOSPHERE OF URANUS Only 1 layer of

methane clouds, as opposed to 3 cloud layers on Jupiter and Saturn. Difficult to see

because of thick atmosphere.

Also shows belt-zone structure. Result of planet’s

rotation rather than sunlight incidence angle.

ATMOSPHERE OF URANUS Keck Telescope in Mauna Kea (Hawaii) show

clear variability of the cloud structures. Possibly due to extreme seasonal changes

INTERIOR OF URANUS Average density ~ 1.29 g/cm3

Larger portion of rock and ice than Jupiter and Saturn, thus higher density.

URANUS’ MAGNETIC FIELD Lower mass than Jupiter; internal pressure not high

enough to create liquid metallic Hydrogen. No magnetic field was expected.

Voyager 2 detected slight magnetic field (75% of Earth’s).

Theorists say it is generated by a dynamo effect not from the interior like on Earth and other planets, but from surface layers of liquid water with dissolved ammonia and methane (convection currents) good conductor of electricity, rotation coupled together = magnetic field.

URANUS’ MAGNETIC FIELD Rapid rotation and large inclination deform

the magnetosphere into a corkscrew shape.Aurora and radiation belts detected.

RINGS OF URANUS Similar to Jupiter’s

rather than Saturn’s. Dark/faint, not easily

visible, and contained by shepherd satellites.

Like all Jovian rings, they cannot survive for long periods; need to be replenished with material from impacts on moons.

RINGS OF URANUS

MOONS OF URANUS 5 largest moons visible from Earth.

Tidally locked to Uranus.

10 more discovered by Voyager 2.

Dark surfaces; probably ice darkened by dust from meteorite impacts. Large rocky cores surrounded by icy

mantles.

TitaniaLargest moon of Uranus

MOONS OF URANUS Miranda is the innermost and most

unique of the moons of Uranus. Originally believed to be

broken apart and accreted back together.

Consists of ovoids, or oval-grooved patterns most likely associated with convection currents in the mantle, not with impacts.

Old surface features suggest Miranda is no longer active.

HISTORY OF URANUS

Difficult to study and observe. Far away/peculiar in many ways.

Computer models suggest it probably formed closer to the Sun, along with Neptune, in the field of Jupiter and Saturn. Gravitational interactions may

have eventually moved them outward to their present locations.

Interesting hypotheses exist.

URANUS“God of the Sky”

NEPTUNE Discovered in 1846 at a

position predicted from gravitational disturbances on Uranus’ orbit. J.C. Adams

U.J. Leverrier

Blue-green color exists from methane gas being present; similar to Uranus. 30.1 AU’s from the Sun.

Approximately 4 times the Earth’s diameter.

Rotation ~ 16.05 h

Revolution ~ 164.8 y

NEPTUNE’S ATMOSPHERE

Belt-zone structured clouds with high speed winds; similar to other Jovians.

Great Dark Spot similar cyclonic disturbance to Jupiter’s Great Red Spot.

White cloud features on the planet are methane-ice crystals.

NEPTUNE’S RINGS Voyager 2 revealed rings of

Neptune, as expected. Can’t be primordial they couldn’t

have lasted in their present form since the formation of Neptune.

MOONS OF NEPTUNE 2 largest moons of Neptune visible from

Earth-based telescopes; Triton and Nereid. 6 more discovered by Voyager 2.

The orbit of Nereid is highly eccentric compared to the orbit of Triton.

TRITON Only satellite in the

solar system to orbit clockwise (retrograde - backwards). Low surface temperature

~ 35 K

Surface composed of ices: Nitrogen, Methane, Carbon Monoxide, Carbon Dioxide. The cycle of Nitrogen on

Triton resembles in some ways the cycle of Carbon Dioxide on Mars.

HISTORY OF NEPTUNE Like Uranus, Neptune’s

hazy atmosphere with changing cloud patterns, hides a mantle of partially frozen ices astronomers predict dynamo effect generating a magnetic field.

Satellite system suggests a peculiar history: Triton retrograde rotation

Nereid long-period; highly elliptical orbit.

NEPTUNE“God of the Sea”

PLUTO Discovery Clyde Thombaugh;

1930. Sensed something was wrong from the

first moment he saw it.

2.5 magnitudes too faint.

Not the 7-Earth mass planet as predicted.

Difficult to observe from Earth.

Average density ~ 2.0 g/cm3

65% the diameter of Earth’s moon.

Most planetary orbits are nearly circular; Pluto’s is highly eccentric.

1979 – 1999 Pluto was actually close to the Sun than Neptune was. Never collide because Pluto’s orbit is

inclined 17; don’t come close.

PLUTO“God of the Underworld”

SURFACE OF PLUTO Little surface detail is shown, even

from the Hubble Space Telescope.

If all goes well, the New Horizons probe, due to arrive in 2015, will send the first close-up images of Pluto and its moons.

Cold enough to freeze most compounds you think of as gases. Maximum daytime temperature ~ 55K

(-360 F); enough to vaporize some of the Nitrogen and Carbon Monoxide and some Methane to form a thin atmosphere around Pluto. Atmosphere first detected in 1988.

PLUTO’S MOONS Largest moon,

Charon, was discovered in 1978. Half the diameter of

Pluto.

Believed to contain 35% ice and 65% rock material.

Two smaller moons, Nix and Hydra, were found in 2005 and confirmed in 2006 by the Hubble Space Telescope.

ORIGIN OF PLUTO Believed to have a very different

history than its neighboring four Jovian planets.

Pluto and its moons are now considered members of the Kuiper Belt, icy objects beyond Neptune’s orbit (similar to Asteroid Belt between Mars and Jupiter only much larger).

Because of its different origin from the planets,

Pluto is now classified as a dwarf planet.

OBJECTS BEYOND NEPTUNE In recent years, astronomers have discovered

hundreds of objects beyond Neptune’s orbit and have termed them Trans-Neptunian Objects (TNO’s).

Most are just small chunks of ice.

TNO’s exist in a region known as the Kuiper Belt.

FAMILY OF DWARF PLANETS In order to be considered a dwarf planet, the object

must meet the following criteria:

1. Orbits the Sun

2. Is round because of its own gravity (mass-related)

3. Has not cleared the region around its orbit

4. Is not a satellite of another planet

CERES

The largest asteroid

Member of the Asteroid Belt

900 km diameter

ERIS

The “10th” planet

4% larger than Pluto

27% more massive than

Pluto

70% further away from the Sun than Pluto