Greenhouse Effect

• Earth absorbs energy from the Sun and heats up

• Earth re-radiates the absorbed energy in the form of infrared radiation

• The infrared radiation is absorbed by carbon dioxide and water vapor in the atmosphere

Global Warming

• Excessively “politicized” topic

• Very complex problem scientifically

• Slow changes over long periods of time

• Sources of heating, sources of cooling themselves are temperature dependent

Hard Facts: Measurements

• Undisputed: global temperatures go up

Man-made CO2 in the Atmosphere goes up

Correlation: Temperatures rise when Carbon Dioxide levels rise

• This is true since prehistoric times

The Last Millennium – “Hockey Stick”

The Jovian Planets

Jupiter

Uranus

Saturn

Neptune

Comparison

• Terrestrial– close to the Sun– closely spaced orbits– small radii– small masses – predominantly rocky– high density– solid surface– few moons– no rings

• Jovian– far from the Sun– widely spaced orbits– large radii– large masses – predominantly gaseous– low density– no solid surface– many moons– many rings

History• Jupiter and Saturn known to the ancients

– Galileo observed 4 moons of Jupiter and Saturn’s rings

• Uranus– Discovered telescopically by William Herschel in

1781 (actually barely visible to naked eye)

• Neptune– Predicted from observed perturbations of Uranus's

orbit: Adams (1845) and Leverrier (1846)– Observed by Galle (1846) – Discovery great triumph for computational

astronomy/physics

Grand Tour of Voyager 1 & 2

• Used gravitational slingshot to get from planet to planet

Positions in Solar System

• Jupiter: 5 A.U. distance from sun,

takes 12 years to go around the sun

• Saturn: 9.5 A.U. distance,

Saturn year= 29 Earth years

• Uranus: 19 A.U. distance,

Uranus year= 84 Earth years

• Neptune: 30 A.U. distance,

Neptune year= 164 Earth years

(all numbers approximate)

Rotation• About 10 hours for Jupiter and Saturn; about 17 hours

for Uranus and Neptune• Differential rotation: rotation speed varies from

point to point on the “surfaces”– Gaseous bodies with no solid surfaces!

– On Jupiter, the equatorial regions rotate 6 minutes slower than polar regions

– On Saturn the equatorial region is about 26 minutes slower

• Tilt of rotation axes:– Jupiter: almost none – no seasons!

– Saturn, Neptune: about like Earth

– Uranus: weird

Uranus’s Strange Seasons

Jupiter’s Atmosphere

• Cloud bands parallel to equator

• Great Red Spot– First observed in

1664 by Robert Hooke

Jupiter’s Atmosphere

• 86% Hydrogen, 14% Helium; some methane, water, ammonia

• Several layers of clouds: ammonia, ammonium hydrosulfide, water

• Colors mostly due to compounds of sulfur and phosphorus

Jupiters’ Bands: Zones and Belts

• Belts: cool, dark, sinking

• Zones: warm, bright, rising

• Jovian weather mostly circles the planet due to high rotation rate

• Bands exhibit east–west flow Great Red Spot lies between regions of opposite wind flow

Great Red Spot

• About twice the diameter of the Earth

• A hurricane that is hundreds of years old!

Saturn’s Atmosphere

• 92% Hydrogen 7% Helium; some methane, water, ammonia

• Belt structure similar to Jupiter’s, but fainter

• Storms are rarer• White spot seen,

1990 (Voyager)

Uranus’ and Neptune’s Atmospheres

• Ammonia frozen out; more methane– Methane absorbs red light, leads to bluish color

• Almost no band structure on Uranus

Neptune’s Dark Spot

Magnetospheres

• Very strong – Jupiter's extends past the orbit of Saturn!

• Indicate the presence of conducting cores

Rings

Saturn

Jupiter

Uranus

Neptune

Saturn

• Rings composed of small, icy fragments, orbiting in concentric circles

• Orbits obey Kepler’s laws (of course!)– Inner rings move faster

than outer ones

Visibility of Saturn’s Rings

2009

How Do They Form?

• Miscellaneous debris• Moons or other small

bodies torn apart by tidal forces

• Roche limit – distance inside of which an object held together by gravity will be pulled apart

Ring Formation

• Rings may be short lived (on the time scale of solar system)

• Means that they must form fairly frequently• A moon may pass too close to a planet

(within the Roche limit) and be destroyed by tidal forces– This will probably happen to Triton (a moon of

Neptune) within 100 million years!

Moons

• Big moons: Earth’s moon, Jupiter’s Galilean Moons (Io, Europa, Ganymede, Callisto), Saturn’s Titan, Neptune’s Triton diameters >2500 km, largest: 5260 km

• Medium moons: diameter 400-1600 km

e.g. all of Uranus’ major moons

• Small moons: diameter down to 20 km

Jupiter’s Galilean Moons

Io

• Jupiter’s innermost moon

• Size and mass similar to our moon

• Zips around Jupiter in just 2 days

Io• 2 day orbit around Jupiter

(Moon: 28 days)• The most volcanically

active object in the solar system– Heated by tidal friction

• Eruptions as high as 200 miles

Europa

Europa might have liquid water oceans under the surface

Life?

Saturn’s Moons Two-faced looks like Star Wars’ Death Star

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Titan• Titan is the only moon in the solar system

known to have an atmosphere

Infrared picture shows surface details