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 CO 2 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 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 0000 rooftop

Titan Titan is the only moon in the solar system known to have an atmosphere Infrared picture shows surface details