ASTRONOMY 202 Spring 2007: Solar System Exploration Instructor: Dr. David Alexander Web-site: www.ruf.rice.edu/~dalex/astr202_s07 Class 31: Jovian Planets [4/4/07] Announcements Ice Ages and Global Warming Jovian Planets Interiors Atmosphere Magnetosphere Chapter 11 Jovian Moons Planetary Rings Now Playing: Drops of Jupiter - Train
Announcements Homework Observing
Scientists do not know for certain why Earth has been subjected to four Ice Ages. They know that a number of factors interact to produce conditions favoring the formation of ice sheets. Some of these factors include changing continental positions uplift of continental blocks reduction of CO 2 in the atmosphere changes in the Earth's orbit Ice Ages on the Earth http://www.museum.state.il.us/exhibits/ice_ages/ Long ice age intervals did not just suddenly occur. Instead, they seem to have been the culmination of even longer periods of worldwide climatic cooling. This cooling took place for tens of millions of years before the beginning of glaciation. Once ice sheets start to grow, they probably contribute to their own further development. This positive feedback occurs because ice sheets reflect more sunlight back into space than does ground not covered by ice. The reflected sunlight would otherwise warm the Earth's surface.
Ice Ages and the Snowball Earth Ice Ages have occurred frequently throughout the history of the Earth. A lowering of the average global temperature by a few degrees leads to increased snowfall which can cover continents with ice. Very long Ice Ages between 750 and 580 million years ago may have resulted in glaciers at the equator with temperatures low enough for the oceans to freeze. This would have set up a positive feedback system resulting in even colder temperatures. Again the CO 2 cycle comes to the rescue. It takes at least 400,000 years for the Earth to recover from an extreme temperature event.
Long-term Climate Change New Report from Intergovernmental Panel on Climate Change [ Feb 5 2007] Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years (see Figure). The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture. For more information see http://ipcc-wg1.ucar.edu/
Long-term stability The relative uniqueness of the Earth seems to be crucial to the presence of life. If it wasn t for plate tectonics, a geological phenomenon not found on any other solar system planet, the carbon dioxide cycle could not operate and Earth would be a very different place. OR NOT! The fortuity of having plate tectonics may be actually be a result of the distance of the Earth from the Sun and not just luck. In any event, there is clearly a strong interplay between a planet s geology AND it s atmosphere which may result in the presence of life.
The Jovian Planets Jupiter Saturn Uranus Neptune Earth to scale Pictures from Voyager spacecraft While Jupiter and Saturn were studied extensively since the time of Galileo in the 1600 s, it wasn t until the 1760 s that the true scale of these planets was fully realized. Distance then yielded their masses, which in turn gave us an idea of their density.
Bulk Properties of Jovian Planets Jovian planetary atmospheres also contain methane (CH 4 ), ammonia (NH 3 ) and water (H 2 O). In addition, there is acetylene (C 2 H 2 ), ethane (C 2 H 6 ) and propane (C 3 H 8 ).
Rapid Rotation squash the Jovian planets The gas giants rotate much more rapidly than the terrestrial worlds and because of their overwhelmingly gaseous nature the exhibit signs of differential rotation like the Sun. Jovian Days Jupiter/Saturn 10 hours Uranus/Neptune 16-17 hours Jupiter s average rotation velocity is 49,000 km/hr. The excess gravitational pull of the equatorial bulge helps keep the moons and rings of these planets in the equatorial plane.
Jovian Planet Interiors Most of our information about the interiors of the gas giants comes from limited observations and lots of theoretical calculations and modeling. Jupiter s core is about 10 times as massive as the Earth but the same size The rocky core is very different from the terrestrial worlds because of the huge pressures and high temperatures there Metallic Hydrogen is an important component of Jupiter s interior structure as it is responsible for Jupiter s strong magnetic field Jupiter generates a lot of internal heat (it emits twice as much energy as it receives from the Sun)
Interior Structure The composition of the cores of all four Jovian planets is expected to be very similar despite their large range of size and density. Jupiter and Saturn are large enough to have metallic hydrogen and to have liquid cores of rock, metal and H compounds. The cores of Uranus and Neptune are relatively large because they are less compressed by the surrounding gas.