Fountains of Enceladus
1 2016-05-17T12:31:45+00:00 Mariek Schmidt 3b678a5bd42eb8bf9a55fb761e5f17b11ce872c1 10 1 Recent Cassini images of Saturn's moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. The image was taken looking more or less broadside at the "tiger stripe" fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb of the moon. The greatly enhanced and colorized image shows the enormous extent of the fainter, larger-scale component of the plume. Imaging scientists, as reported in the journal Science on March 10, 2006, believe that the jets are geysers erupting from pressurized subsurface reservoirs of liquid water above 273 degrees Kelvin (0 degrees Celsius). This caption was updated on March 9, 2006. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at http://ciclops.org. Image Credit: NASA/JPL/Space Science Institute Date Published: 2005-11-28 plain 2016-05-17T12:31:45+00:00 Internet Archive 543617main_pia07759 image Mariek Schmidt 3b678a5bd42eb8bf9a55fb761e5f17b11ce872c1This page is referenced by:
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Density
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Density is the measure a substance’s mass per unit volume. It is most often represented by the Greek letter rho, ρ. The equation for density is:
ρ = m /V
where m is the mass and V is the volume. Typical units are grams per cubic centimeter (g/cm3), or kilograms per cubic meter (kg/m3).
Relative differences in density will cause a denser, less buoyant substance to sink, while a lighter, more buoyant one will rise. This causes layering (also called density stratification) to occur; the densest stuff will be at the bottom, or closest to the center of gravity, while the lightest will be at the top, or farthest from the center of gravity.
For the case of a differentiated rocky body, its center is also its center of gravity. Solid iron metal is the densest and is thus found at the center of gravity. Crusts of terrestrial planets are commonly rich in a low-density silicate mineral called plagioclase feldspar, and are found farther away from the center of gravity.
One of the lines of evidence that the Earth has a dense core is that the mass of the Earth is much greater than can be attributed to rocks seen at the surface. Basalt is a typical crust rock for terrestrial planets. The density of basalt (3.2 g/cm3) is significantly less than the mean density of the Earth (5.52 g/cm3). Therefore, there must be a very dense core.
Relationship between density and temperature
The volume of a substance correlates with temperature; when a substance heats up, its volume expands, and when the substance cools down, the volume contracts. An example of this phenomena is your car tires. In the winter, it is common for the air in your car tires to contract from the cold, causing your tire pressure to go down and the warning light on your dash to go on. But once you drive around for awhile, your tires warm up, and the tire pressure light will go away. (Unless you really do have a flat tire!)
So now let’s think about how the changing volume with temperature affects density. Density is mass per unit volume. With increasing temperature, the mass stays constant, but it is spread out over a larger volume, causing density to decrease. Conversely, with decreasing temperature, mass stays constant, but it is squeezed into a smaller volume, and density increases. Density is therefore inversely proportional to temperature (when temperature goes up, density goes down).
This relationship between temperature, density and buoyancy is really well illustrated by a lava lamp. Be groovy and impress your friends by teaching them how a lava lamp works:
For the planets, changes in density related to changes in temperature drive important geologic processes, including- the rise of hot magma (molten rock) relative to surrounding colder rock,
- the rise of hot fluids and eruptions of geysers on Earth, or Saturn’s moon Enceledes,
- mantle convection and plate tectonics, which in turn governs the distribution of volcanoes and earthquakes on the Earth. (This is a really, really important process for the Earth, so stay tuned for the next module.)