Chapters 23 and 24:The Jovian Planets (“Gas Giants”):

Jupiter, Saturn, Uranus, Neptune

Galileo’s view of Saturn. He could not see that the “lobes” were rings, and did not understand why they sometimes disappeared.

Matthew Day

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Ming-Hua Chang

Images of Saturn taken by students at Seattle University

Saturn -- Hubble Space Telescope

Saturn’s most striking feature is its ring system

Saturn: Voyager 2

Cassini Spacecraft View of Saturn

Saturn’s Ring system, by Cassini

Close-up of clouds on Saturn

Gas giants (Jovian planets)• Are mostly gases (H, He, H2O, CH4, NH3); the rest = ice + rock• Have no solid surface: gases --> solid at high pressure• Have ring systems and many moons• Form faster, and in a different way, compared to terrestrial planets:

large enough to accumulate gas directly from the solar nebula• They are far from the Sun (in the case of the solar system)• So far, all known extrasolar planets are gas giants, but they are all

close to their parent star (why?)

Jupiter, imaged with theHubble Space Telescope

Colorful cloud bands are the most striking characteristic of the planet, and the Great Red Spot

Uranus

Neptune: Its existence was predicted because Uranus did not seem to obey Kepler’s Law!

Images taken by the Voyager 2 spacecraft

The giant planets are much more massive and less dense than EarthThey rotate much faster than Earth

Gas giants rotate differentially: rotation is faster at their equator than their poles (like which other object in the solar system??They all have magnetic fields (molten interiors)

318 MEarth

15 MEarth 17 MEarth

95 MEarth

Belts and zones on JupiterDifferential rotation

Jupiter’s most distinguishing features:

• The Great Red Spot• Cloud bands• the “Galilean moons”

Storms on gas giants last so long because there are no continents over which they can lose their energy and dissipate

What causes Jupiter’s cloud bands?• Strong winds and Jupiter’s differential rotation produce

bands parallel to equator• hydrogen, helium, water (H2O),

ammonia (NH3) and methane (CH4)

• These gases are colorless, and their ices are white

• Colors due to sulfur compounds and organic hazes particles (?)

• Sunlight and lightning affect the chemistry of Jupiter’s atmosphere

Clouds and convection in Jupiter’s atmosphere

Zones: high pressure, lighterBelts: Lower pressure, darker color

Rotation channels the winds into east-west pattern that wraps around entire planet

Zonal flow: stable eastward and westward winds deeper in the atmosphere 300 km/hour easterly, at equator0 at poles - bands disappear

Entry site of Galileo Probe: the first man-made object to enter the atmosphere of a giant planet

Saturn is not as colorful as Jupiter, but does have bands and storms Saturn has less hydrogen and helium than Jupiter, and the ratio of helium to hydrogen is much lower: why?

Helium seems to have liquified and sank to Saturn’s center

Helium precipitation seems to be the cause of Saturn’s energy output

Like Jupiter, Saturn has:• bands• oval storm systems• turbulent flow patterns• stable east–west zonal flow • wind speed is > Jupiter with fewer east–west alternations.• The equatorial eastward jet stream = 1500 km/h

color enhanced

Storms on Saturn are more rare than on Jupiter

In 1990, a storm developed in Saturn’s equatorial region and soon completely encircled the planet.The storm dissipated in a few weeks.

Uranus Neptune

Both worlds are composed mostly of hydrogen and heliumAmmonia is in the form of ice crystals (snow), not as a gasMethane gives these planets their blue color : absorbs red and yellow photons from sunlight, reflects blueNeptune has more methane than Uranus

Uranus• Does not have distinct atmospheric

features (storms, bands, etc.) the way Jupiter does

• No high-altitude clouds; deeper features are obscured by haze layer

• Clouds move around planet in same direction as rotation (200-500 km/hour)

• colder than Jupiter & Saturn (53 K)• has a thin ring

computer enhanced

Uranus’ axial tilt is 98o -- compared to Earth’s 23o tilt

New hypothesis of Uranus and Neptune formation: they originally formed between Jupiter and Saturn (5-9 AU) and migrated outward!

Neptune

• Slightly warmer than Uranus even though further from Sun

• temperature = 59 K• Haze layer not as thick• Has more obvious features than

Uranus: storms, spots, bands• slightly more massive than

Uranus• 2000 km/hour winds -- much

faster than Uranus• The Great Dark Spot lasted only

a few years

Using a telescope with a spectrometer, we can observe the wavelength at which Neptune radiates most of its photons. From Wien’s law,

max = 0.29T

cm

Neptune, max = 0.005 cm, so Neptune’s temperature = 59 K

if it were only heated by the Sun, Neptune should be 50 K.

Neptune has an internal source of energy: unknown at this time!

Neptune’s Great dark Spot, discovered by Voyager 2 in 1989

Neptune, imaged by the Hubble Space Telescope

Great Dark Spot is gone by 1994

Atmospheric structure changes over just a few days’ time

Computer-enhanced images of Neptune from Hubble Space Telescope

Seasons are changing!

Laws of physics and chemistry + observations = model for giant planets

• All 4 giant planets have about the same mass rocky core (10 Mearth)

• J & S have much more hydrogen & helium than U & N

• J & S have metallic hydrogen• J & S & N radiate away more energy

than they receive from Sun

Aurorae on earth: Interaction of solar wind with Earth’s magnetic field

The Earth has the properties of a big magnet

Solar wind (charged particles) respond to this magnetic field

The giant planets all have magnetic fields, & atmospheres, so we expect them to have aurorae too!

Jupiter’s magnetosphere is affected by the solar wind

We can measure the strength of J’s magnetic field : much stronger than Earth’s

Formation of the gas giant planets:Gas giants form via core accretion followed by accumulating H and He gases from the solar nebula. In the solar nebula, ice was an abundant core-building material > 5 AU from the Sun, because temperatures drops as you go further from the Sun

Gas giants must form before the solar nebula dissipates (< 10 million years)

Disks are seen around many young stars

Jupiter

Earth

Jupiter and Saturn’s atmospheres to scale

cooler than Jupiter, less dense atmosphere, thicker cloud layers