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