12. Jovian Planet Systems Pearson Education Inc., publishing as Addison Wesley

Transcription

1 12. Jovian Planet Systems

2 Jovian Planet Properties Compared to the terrestrial planets, the Jovians: are much larger & more massive 2. are composed mostly of Hydrogen, Helium, & Hydrogen compounds 3. have no solid surfaces 4. rotate more quickly 5. have slightly squashed shapes 6. have many moons 7. have ring systems

3 Jovian Planet Properties

4 Jovian Planet Properties

5 Why are the Jovian Planets so Different? They formed beyond the frost line to form large, icy planetesimals which were massive enough to Capture H/He far from Sun to form gaseous planets. Each Jovian planet formed its own miniature solar nebula. Moons formed out of these disks.

6 Inside Jupiter Although Jupiter has no solid surface and consists mostly of H & He, it does have distinct interior layers, defined by phase. metallic hydrogen Moving from the surface to the core: temperature increases 2. pressure & density increases The core of Jupiter is slightly larger than Earth. But it is 5 times as dense! thank to tremendous weight from above So Jupiter's core has 10 times the mass of Earth.

7 Inside Jupiter 2. Jupiter emits almost twice as much energy as it absorbs from the Sun. accretion, differentiation, radioactivity can not account for it Jupiter must still be contracting Jupiter has 3 x more mass than Saturn, but is not much larger! the added weight of H & He compresses the core to a higher density 2. just like stacking pillows Add even more mass, and Jupiter would get smaller. Jupiter is about as large as a planet can get. Uranus & Neptune have less mass than Saturn, yet have higher densities they must be made of denser material

8 Inside the Jovian Planets All Jovian cores appear to be similar. made of rock, metal, and Hydrogen compounds, but not solid! about 10 x the mass of Earth Uranus & Neptune captured less gas from the Solar nebula. accretion of planetesimals took longer? not much time for gas capture before nebula was cleared out by Solar wind? Only Jupiter and Saturn have high enough pressure for H & He to exist in liquid and metallic states.

9 Interior models of the giant planets Jupiter and Saturn Gas giants only small fraction of mass is not H and He(Y) Upper layers of Saturn He depleted Uranus and Neptune Most of the mass is ices with some rock Only upper layer is dominantly H and He

10 Jupiter s Atmosphere In 1995, the Galileo space probe plunged into the planet Jupiter! It measured the atmospheric structure of Jupiter Sound Familiar? thermosphere {absorbs Solar X rays} 2. stratosphere {absorbs Solar UV} 3. troposphere {greenhouse gases trap heat from both Jupiter and the Sun} These are the same structures found in Earth s atmosphere. Atmospheres are governed by interactions between sunlight and gases.

11 Jupiter s Cloud Layers Convection in the troposphere causes Jovian weather. Warm gas rises to cooler altitudes, where it condenses to form clouds. Three gases condense in the Jovian atmosphere: ammonia (NH3) ammonium hydrosulfide (NH4SH) water (H2O) They condense at different temperatures, so their clouds form at different altitudes.

12 Like Earth, Jupiter has circulation cells in its atmosphere. Jupiter is much larger & rotates much faster. Jupiter s Cloud Layers Coriolis effect is much stronger on Jupiter 2.circulation cells are split into many bands of rising and falling air 3.these are the colored stripes which we see

13 A recent picture Taken by the Cassini spacecraft on its way to Saturn during a gravitation flyby of Jupiter Beautiful and complex cloud structure as we see to different depths down into the jovian atmosphere

14 Jovian planet Storms We also see high pressure storms analogous to hurricanes, but they rotate in the opposite direction 2. Jupiter the Great Red Spot we are not sure why it is red 3. Neptune the Great Dark Spot

15 Saturnian cloud structure Recent Cassini orbiter image of Saturn (note Mimas also)

16 The Jovian Atmospheres The temperature profile of each planet determines the color of its appearance. Cloud layers form where a particular gas condenses. Saturn has the same cloud layers as Jupiter. they form deeper since Saturn is colder overall 2. they are spread farther apart since Saturn has lower gravity Uranus & Neptune cold enough to form methane clouds

17 Why Uranus & Neptune are Blue They have a higher fraction of methane gas. Methane absorbs red sunlight. 2. Only blue light is reflected back into space by the clouds. Uranus is tipped on its side. It should experience the most extreme seasonal changes Visual 1998 IR no clouds or banded structure seen in 1986 when N pole facing Sun 2. no weather > no internal heat? 3. HST saw storms starting 1998, b/c the S hemisphere is warming now

18 Earth's magnetic field + aurorae

19 Jupiter s Magnetosphere Its general properties are very similar to Earth s, except it is about 20,000 times stronger (radio detection) 2. it extends 3,000,000 km beyond Jupiter Charged particles from the Solar wind (& Io) cause auroras.

20 The Io Torus The moon Io loses volcanic gases into space. gases are ions on Sulfur, Oxygen, Sodium 2. They are trapped by Jupiter's rotating magnetic field and pulled along 3. they form a donut shaped belt of charged particles, called the Io torus

21 Jovian Magnetospheres Saturn, Uranus, & Neptune have smaller & weaker magnetospheres. fraction of electrically conducting material in interiors is smaller 2. we do not understand the magnetic field tilts of Uranus & Neptune.