Shop Windows to the Universe

The Spring 2011 issue of The Earth Scientist is focused on modernizing seismology education. Thanks to IRIS, you can download this issue for free as a pdf. Print copies are available in our online store.
An artist's depiction of what the scene must have looked like when the NASAís Galileo spacecraft approached Amalthea, moon of Jupiter.
Click on image for full size
Courtesy of NASA

A Jupiter moon that has more holes than Swiss cheese!
News story originally written on December 11, 2002

Amalthea , a small moon of Jupiter, is not made of Swiss cheese, but it does seem to be full of holes making its density surprisingly low.

Roughly the shape of a potato, Amalthea is a small, reddish moon that is about 270 km (168 miles) in length and about half as wide. We know very little about the composition of most small moons, but now the Galileo spacecraft has provided us with some interesting information about what makes up Amalthea.

To figure out the density of Amalthea, scientists needed to know the mass and the volume of the moon (because, as you may know, density=mass/volume). They calculated the mass of Amalthea from its gravitational affect on the Galileo spacecraft, which passed 160 km (99 miles) from the moon. The volume of the moon was calculated from images like the one on the left.

They found that Amalthea has very low density. Scientists at the NASA Jet Propulsion Laboratory suggest that the rock that makes up Amalthea is broken into many pieces that are about the size of large boulders. The pieces are just barely touching each other leaving many empty gaps in the moon. ďThis finding supports the ideas that the inner moons of Jupiter have undergone intense bombardment and breakup. Amalthea may have formed originally as one piece, but then was busted to bits by collisions,Ē said Dr. Torrance Johnson, project scientist for Galileo.

However, the new findings about Amalthea do not fit with all the pervious theories about Jupiterís moons. One of these theories describes the formation of Jupiterís moons suggesting that moons closer to the planet, like Amalthea, would be made up of denser material than those farther out. Jupiterís four largest moons fit this model, however, Amalthea's rocky material could not be denser than the rocks that make up the neighboring moon Io.


Last modified December 11, 2002 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

Our online store includes fun classroom activities for you and your students. Issues of NESTA's quarterly journal, The Earth Scientist are also full of classroom activities on different topics in Earth and space science!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

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

Density Definition Page

Density is a measure of how much mass is contained in a given unit volume (density = mass/volume). It is usually expressed in kg/m^3, so you would say that a cube 2 meters on each side with a mass of 16...more

Galileo

The Galileo spacecraft was launched on October 19, 1989. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. Galileo's primary mission was to explore the Jovian...more

What is mass?

Would it be more difficult to pull an elephant or a mouse? If you pulled each animal with the same amount of force, the elephant would respond less to pulling, even if he didnít pull back at all. Thatís...more

1999--A Year in Review...

It was another exciting and frustrating year for the space science program. It seemed that every step forward led to one backwards. Either way, NASA led the way to a great century of discovery. Unfortunately,...more

STS-95 Launch: "Let the wings of Discovery lift us on to the future."

The Space Shuttle Discovery lifted off from Kennedy Space Center at 2:19 p.m. EST, October 29th. The sky was clear and the weather was great as Discovery took 8 1/2 minutes to reach orbit for the Unitied...more

Moon Found Orbiting Asteroid

A moon was discovered orbiting the asteroid, Eugenia. This is only the second time in history that a satellite has been seen circling an asteroid. A special mirror allowed scientists to find the moon...more

U.S. is Fed Up with Russia

Will Russia ever put the service module for the International Space Station in space? NASA officials are demanding an answer from the Russian government. The necessary service module is currently waiting...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