The Outer Planets

Cosmic Abundance of ElementsHydrogen H 1 1,000,000

Helium He 2 80,000

Carbon C 6 363

Nitrogen N 7 112

Oxygen O 8 851

Neon Ne 10 117

Sodium Na 11 2

Magnesium Mg 12 32

Aluminum Al 13 3

Silicon Si 14 45

Sulfur S 16 16

Argon Ar 18 1

Calcium Ca 20 2

Iron Fe 26 36

Nickel Ni 28 2

Major Constituents

Gas Formula Jupiter Saturn

Hydrogen H2 86% 92%

Helium He 14% 7%

Methane CH4 0.2% 0.2%

Ammonia NH3 0.02% 0.02%

Water H2O ~0.2% (?) ~0.4% (?)

Interiors: Big H2 Atmospheres

Jupiter vs Saturn

Jupiter’s Ammonia Clouds:

Belts: Dark bands

Zones: Bright bands

Great Red Spot

White Ovals

The GRS has lived at least 300 yrs. Ovals have been seen to survive tens of years

Jupiter’s clouds result from convection.

1) Hot air expands.

2) Lighter than the rest of the air, it rises.

3) As it rises, it cools and condenses forming clouds.

4) When it is cooler than the ambient air, it sinks.

Great Red Spot

Saturn’s Clouds

Uranus

Absorption of sunlight at red wavelengths by methane renders the planet blue.

Neptune

Neptune emits more energy from its interior than does Uranus. This energy drives weather. The colder temperatures cause methane to condense in the upper atmosphere – these are the clouds that we see.

Moons

A typical, heavily cratered, terrain.

Saturn’s moon, Tethys

Their densities tell us that they are ½ rock & ½ ice.

Jupiter’s Moons

Callisto

Heavily cratered surface with small areas of spiky landscape. This is hypothesized to be caused by sublimation (vaporization) of ices on surface.

Image from the Galileo Spacecraft

Ganymede: 1km relief

Largest moon

½ of the surface is dark and heavy cratered.

The other ½ is younger, less cratered. It appears to be faulted and, at places, depressed. The low areas appear to be subsequently flooded.

This grooved terrain indicates recent geological activity.

Europa

Few craters

A terrain containing elements that were recently dislodged can be seen to neatly fit together if rotated and translated in position.

Io

• Images\iovol_vgr.gif

Io

What fuels Io?

Each time Ganymede orbits once, Europa orbits twice, and Io orbits 4 times.

Plumes fountain 500 km above the Surface

Io’s surface is almost devoid of craters, for it is being repaved at a rapid rate.

The glow of warm lava.

A pool of lava (black) covered with sulfur deposits (orange). This is called Tupan Patera after the Brazilian thunder god.

Images taken from the Galileo spacecraft.

Io is hot

Lava flows on Io exceed 1500 K in temperature. Lavas this hot are not sulfur (which would evaporate immediately). This is hotter than present lavas on Earth (1300-1450 K). Instead these lavas are likely ultramafic (rich in Mg and Fe), similar to the lavas that occurred on early Earth.

Present hypothesis, a ~100 km thick crust floats on top of a worldwide ocean of magma 800 km deep.

Titan: a moon with an atmosphere

Home Work

Ch.17

DQ: 1, 12

Problem 9

Ch. 21

DQ: 19, 20

Problem 3

Observações da alta atmosfera

Composition of Titan’s stratosphere Molecule Abundance

N2 65-98%CH4 2-10%H2 0.2-0.6%CO 6-150 ppmCH3D 5-180 ppmC2H6 13-20 ppmC2H2 2-5 ppmC3H8 0.5-4 ppmC2H4 0.09-3 ppmHCN 0.2-2 ppmHC3N 80-250 ppbCH3C2H 4-60 ppbC4H2 1-40 ppbC2N2 5-16 ppbCO2 1.5-14 ppb

Derived from radiative transfer analyses of Voyager, ISO and ground-based data.

Titan’s Surface

HST images

Peter Smith & Co

U. of Arizona

Oceans?CH4

C2H6

C2H2

haze

γ + CH4 -> other hydrocarbons

Methane in atmosphere is depleted in107 years.

Either methane is supplied or we are witnessing Titan at a particular moment in its history.

Oceans containing methane explain the near saturated tropospheric conditions,provide a source for methane, and don’t requirea penchant for being lucky.

Flasar et al. Science 221, 55Lunine et al. Science 222, 1229

Ocean (CH4, C2H6, N2)

hν

From the Cassini Huygen’s Website

Cassini-Huygens spacecraft, on a Titan IV rocket, waiting for takeoff.

15 15 October 1997

A perfect takeoff that saved fuel.

Testing Cassini(Jet Propulsion Laboratory, California)

We can see the main antenna.

All the instruments (e.g. the cameras) are covered.

Huygens Probe,European SpaceAgency

We can see the shield that protects the instruments against the heatof entry into theatmosphere.

In 2005, the desent of Huygen’s into Titan’s atmosphere.

At 170 km altitude, Huygens releases the shield and beginsmeasurements.

STAY TUNED IN !

Triton Neptune’s Largest Moon:

Triton

On Triton the main component of the atmosphere, nitrogen, exits in vapor pressure equilibrium.

That is, it exists as an ice on the surface and as vapor in the atmosphere, in the same way that water exists as liquid and ice on Earth’s surface and as a gas in the atmosphere.

The amount of gas depends on the temperature. Less exists at cooler temperatures.

This is seen on Earth with the condensation of water at dew point.

Atmosphere:

1.6x10-7 bar 38K Nitrogen

Rings

Ring particles are ice fragments, 1 cm to 10 m in size, that orbit Saturn.

The rings span 70,000 km and are only 20 meters thick!

There are many gaps in the rings as well.

Jupiter’s Rings

Silicate dust, 10,000 times more transparent than window glass.

Uranus’ Rings

Rings are made of dark material, unlike ice, and postulated to be carbonaceous.

The rings are made up of a bunch of narrow rings, separated by larger gaps.

Neptune’s RingsNarrow rings of varying density

What causes Ring Structure?

The interaction of ring particles with moonlets.

Cordelia and Orphelia orbit 2000 km on either side of Uranus’ Epsilon Ring.

Uranus’ rings and a couple of shepherds

GapsEmbedded moonlets can sweep clear a lane much larger than its diameter, thus causing gaps like the Cassini Division.

Roche Limit

The distance between a planet and 2 particles (m1 and m2) such that:

The difference in the gravitation attraction of the inner and outer mass to the planet exceeds the gravitational attraction between m1 and m2

Summary

• Giant planets are large gas planets with nearly solar elemental abundances.

• They have small ice-rock cores. • Their moons are ½ rock and ½ ice. • Most moons display heavily cratered terrains. Io, Europa,

Triton and Titan are exceptions. • All jovian planets sport rings of differing thicknesses,

compositions & character. • Titan supports an atmosphere second only to Venus’

(considering bodies with proper surfaces). It is rich with organics, and its origin is unknown.

• The Cassini mission to the saturnian system is in route and functioning well.