2. The ‘Greenhouse Effect’ and the ‘Enhanced Greenhouse Effect’
Greenhouse Effect
description
Transcript of Greenhouse Effect
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
0000rooftop
Titan• Titan is the only moon in the solar system
known to have an atmosphere
Infrared picture shows surface details