Shop Windows to the Universe

Hands On Mineral Identification helps you to identify over 14,500 minerals! By M. Darby Dyar, Ph.D. See our DVD collection.
This is a drawing of the interior of Jupiter's moon Ganymede.
Click on image for full size
NASA

How do we know what the inside of a Planet or Moon is like?

You may wonder how it is that scientists know what the inside of a planet is like.

The way the mass of a body is spread inside the body affects how the body spins in space. If the body has a large core, it will spin with a certain speed, if it has no core it will spin at another rate of speed. The affect is like that of an iceskater who spins faster when her arms are close to the body than when the arms are spread apart.

By studying the rate of spin of a body, as well as determining the mass of the body, scientists can figure out if the body must have a core and how large that core must be.

The picture shown here is that of Jupiter's moon Ganymede, and illustrates that spacecraft measurements were able to determine that the moon has at least two layers inside, besides the surface crust (scientists think that there are really three layers). Scientists must still use theories to estimate exactly what the layers are made of.


Shop Windows to the Universe Science Store!

Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, ranging from seismology, rocks and minerals, oceanography, and Earth system science to astronomy!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Interior of Ganymede

The picture on this page shows what the inside of Ganymede looks like. Scientists have made this model based on measurements by the Galileo spacecraft. The picture shows a samll core of metal (silver),...more

The Moon's Magnetosphere

Unlike the Earth, which has a protective shield around it called the magnetosphere, the surface of the moon is not protected from the solar wind. This picture shows the magnetosphere surrounding the Earth,...more

The Viking Missions

The Viking I and Viking 2 missions were to both orbit Mars and land on the planet's surface. There were two spacecraft for each mission. At this stage in the history of the exploration of Mars, scientists...more

AU

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 Spiral of the IMF

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

Spiral Path of Material

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

The SAR Arc

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

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA