There are many instances in planetary science where the same material can come in different forms. An example of one such instance is shown in this picture. A diamond is one form of pure carbon, and graphite (what goes into pencil lead) is another form of the same material. They are both made of the identical substance (carbon), but they have a very different size and structure. The difference in molecular construction is referred to as the "phase" of carbon. Graphite is a different phase of carbon than that of diamond.
One might be able to imagine two different moons made out of the same amount of carbon, but one moon made of graphite and the other made of diamond. The two imaginary moons would have very different sizes! Then one might imagine one moon evolving into the other, and having to change sizes as it does so. This phenomena explains the evolution of the icy moons. Ice comes in nine different phases, and all of them have a different molecular construction. In it's evolution, an icy moon may change many times from one phase to another, or include many different phases in it's interior.
Two other materials, from the earth's interior, which have similar phase differences are olivine and spinel.
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
The mineral that is green is called olivine! Look for it in igneous and metamorphic rocks. In this picture, olivine is filling a hole in the igneous rock. ...more
AU stands for Astronomical Units. It is an easy way to measure large distances in space. It is the distance between the Earth and the Sun, which is about 93 million miles. For really big distances, we...more
The solar wind is formed as the Sun's top layer blows off into space. It carries magnetic fields still attached to the Sun. Streams appear to flow into space as if they are spiraling out from the Sun,...more
For a planet to be affected by a blob of material being ejected by the sun, the planet must be in the path of the blob, as shown in this picture. The Earth and its magnetosphere are shown in the bottom...more
If someone says they saw an aurora, you might picture something like this. There is another type of aurora that we can't see. These aurora are called SAR arcs. The SAR stands for Stable Auroral Red. That...more
This figure shows the effect of the aurora on the atmosphere. When FAC's enter the atmosphere and create the aurora, they heat the atmosphere suddenly and abruptly. This creates an impulse which travels...more
This picture shows the flowing of particles into and out of the auroral zone, as Field-Aligned currents (FAC's) take at short-cut through the atmosphere. Some of the particles entering the auroral zone...more