Shop Windows to the Universe

With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.
Europa's fractured, icy surface (top) might be a relatively thin layer floating atop a vast ocean. An artist's depiction of one possible arrangement of Europa's interior (bottom) shows this proposed ocean in blue beneath the moon's outer shell of ice.
Click on image for full size
Images courtesy of NASA/JPL/ASU.

The Icy Galilean Moons of Jupiter

Jupiter has four large moons which are sometimes called the "Galilean moons". Three of the four - Europa, Ganymede, and Callisto - are covered with water ice and are thus similar to Earth's frozen polar regions in various ways.

Although their interiors also contain rocky material, the outermost layers of these three moons are mainly made of water ice. Each of the three, especially Europa, might also have salty "oceans" of liquid water beneath their surface layers of ice. This is reminiscent of Earth's Arctic Ocean, where sea ice floats atop ocean water, and of the subglacial lakes in Antarctica which lay thousands of meters beneath the Antarctic ice sheet.

Astrobiologists are excited about the possibility of finding life in these putative under-ice oceans. They are especially interested in Europa. Like volcanic Io, the only non-icy Galilean moon, Europa's interior is constantly heated due to flexing caused by gravitational tugs from Jupiter and the other large moons. Europa could have geothermal features, like undersea volcanoes or hydrothermal vents, at the bottom of its proposed "ocean layer". On Earth, strange communities of extremophile microbes, enormous tubeworms, clams and crabs thrive around hydrothermal vents on the sea floor. Scientists wonder whether similar organisms could have arisen within the proposed oceans of Europa or the other icy Galilean moons.

A polar explorer from Earth might also see a familiar sight in the skies above these icy moons. The beautiful light shows of the aurora, or Southern and Northern Lights, are often visible above Earth's polar regions. Aurora have been detected at Ganymede, and may occur at Europa and Callisto as well.

Last modified August 3, 2009 by Randy Russell.

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, as well as books on science education!

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

Galilean Satellites

The Galilean satellites are the 4 major moons of Jupiter, Io, Europa, Ganymede, and Callisto. In this picture, Io, and Ios surface, are shown on the left-most end, then Europa, and its surface, then Ganymede,...more

Europa

Europa was first discovered by Galileo Galilei in 1610, making it one of the Galilean Satellites. Europa is Jupiter's 4th largest moon, 670,900 km from Jupiter. With a diameter that is about half the distance...more

Callisto

Callisto was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 8th closest to Jupiter, with a standoff distance of 1,070,000 km. It is the 2nd largest...more

Does Europa Have an Ocean?

The surface of Europa shows many signs of that there may be an ocean under the surface: * flooded terrain * 'freckles' * rafting * 'mushy' craters, and * spreading centers. Taken together, these pieces...more

Sea Ice in the Arctic and Antarctic

Sea ice is frozen seawater. It can be several meters thick and it moves over time. Although the salts in the seawater do not freeze, pockets of concentrated salty water become trapped in the sea ice when...more

Glaciers and Ice Sheets

For a glacier to develop, the amount of snow that falls must be more than the amount of snow that melts each year. This means that glaciers are only found in places where a large amount of snow falls each...more

Interior of Europa

The diagram shows possibilities for the interior structure of Europa. There is a core of rocky material buried inside, overlain with ice of various phases. The diagram shows that there may be an ocean...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