ASTRONOMY 202 Spring 2007: Solar System Exploratio n

Instructor: Dr. David Alexander Web-site: w ww.ruf.rice.edu/~dalex/ASTR202_S07

Class 32: Jovian Planets [4/9/07]

� Announcements

� Jovian Planets

� Interiors� Atmosphere� Magnetosphere

� Jovian Moons

� Planetary Rings

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Interior Structure

The composition of the cores of all four Jovian planets is expected to be very similar despite their large range of size and density.

Jupiter and Saturn are large enough to have metallic hydrogen and to have liquid cores of rock, metal and H compounds.

The cores of Uranus and Neptune are relatively large because they are less compressed by the surrounding gas.

Jovian Planetary AtmospheresLike Earth, the Jovian planets have a complicated atmospheric structure, featuring a troposphere, stratosphere and thermosphere.

The tropospheres are particularly interesting giving a range of dynamic weather features such as clouds, storms and global wind patterns.

Jupiter’s Cloud Cover

Jovian Weather SystemsJupiter’s cloud layers are a result of global wind patterns, altitude variations and composition: ammonia clouds are white, cool and high while the ammonium hydrosulphide clouds are brown, lower and warmer.

Great Red Spot

Great Red Spot is a >300 year old storm which spins in opposite sense to what is expected

Other, shorter lived storms are also seen.

Jupiter’s New Red Spot

The official name of this storm is "Oval BA," but "Red Jr." might be better. It's about half the size of the famous Great Red Spot and almost exactly the same color.

Oval BA first appeared in the year 2000 when three smaller spots collided and merged.

The oval was white in November 2005, it slowly turned brown in December 2005, and red a few weeks ago.

Magnetospheres

Each of the Jovian planet’s is surrounded by a magnetosphere: a bubble of plasma contained by a magnetic field generated in the interior of the planet.

Jupiter’s magnetic field is 20,000 times stronger than the Earth’s and extends some 3 million km towards the Sun.

Magnetospheres and the Moons

Ganymede shows signs of a dense magnetic core and exhibits a strong magnetic field

Volcanic activity on Io populates the inner regions of Jupiter’s magnetosphere with a charged particle belt known as the Io torus.

Jovian Moons

The Jovian planets have over 100 moons between them. Some of them are comparable in size to a small planet like Pluto or even Mercury and a number are larger than the Earth’s Moon.

Saturn’s moon, Titan, has a dense atmosphere while the four Galilean moons of Jupiter, Io, Europa, Ganymedeand Callisto all show interesting geological behaviour.

Io Europa Ganymede Callisto Titan

Volcanoes Ice Geology Magnetic Field Salty Ocean Dense atmosphere

Io : the most volcanically active world in the solar s ystem

Volcanic eruptions on Io’s dark side

Io has so much volcanic activity that no impact craters are evident.

The outgassing from the volcanoes are the source of the large amounts of ionized gas (plasma) in Jupiter’s magnetosphere.

Io loses atmospheric gas faster than any other world in the solar system.

Tidal heatingMoons like Io are too small and too old to be generating significant amounts of internal heat so the source of energy for the volcanism on Io has to be due to something else.

The size and shape of Jupiter together with the closeness and eccentricity of Io’s orbit provides for internal heating due to tidal forces.

Europa : The Water World?

Europa’s surface and crust are made almost entirely of water ice. It also has a metallic core and a rocky mantle.

The cracked structure reveals the presence of tidal heating and suggests a liquid ocean some 100 km thick under the icy crust.

Titan : The Smoggy MoonTitan has a smoggy atmosphere composed mostly of Nitrogen (90%), somewhat like the Earth (77%), with the remainder being made up of Argon, methane and ethane, making Titan warmer than expected (-180oC). Titan has a surface pressure only slightly larger than the Earth’s.

The relatively low proportions of methane and ethane in the atmosphere suggests that it ‘rained’ out and may form liquid oceans on the surface. This is borne out by infrared images of the surface.

Titan may have liquid oceans of methane and ethane topped by a nitrogen atmosphere

Hydrocarbon Lake –Titan South Pole

Hydrocarbon Lake –Titan South Pole

High ridge area including the flow down into a major river channel from

different sources.

Titan volcano?

Enceladus : The stripy moonEnceladus’ surface has a distinctive tectonic structure. Its outer boundary is marked by a series of pronounced tectonic 'gashes' that form a hoop-like boundary, near 60 degrees south latitude. In this image, this fault zone forms the transition region from the presumably older, cratered terrain in the north to the younger, nearly crater-free region in the south.

Plumes of icy material extend above the southern polar region of Saturn's moon Enceladus.

Scientists believe that the plumes are geysers erupting from pressurised sub-surface reservoirs of

liquid water above 273K (0°C).

Planetary RingsThe Jovian planets all display a system of rings comprised of millions of icy particles ranging in size from dust to boulders.

Rings and Gaps Gap Moons Spokes

Pan

Cassini Division

Ring particles are made mostly of water ice and are bright where there are enough particles to scatter sunlight back to us.

Each particle in the rings orbit according to Kepler’s laws.

The rings of Saturn show a large number of features

Planetary Rings

Jupiter

Saturn

Uranus

Neptune