Surf's Up on Europa?
BASED ON NASA/JPL PRESS RELEASE
As Galileo flew just 351 kilometers (218 miles) above the icy moon on January 3, its magnetometer detected directional changes in Europa's magnetic field. Such changes are consistent with fluctuations that could occur if Europa contains a shell of electrically conducting material, such as a salty, liquid ocean.
Right: Fragmented chunks of ice on Europa, similar in appearance to those seen in Earth's polar seas during a springtime thaw. Measurements of Europa's magnetic field, obtained during a close flyby on January 3, 2000, suggest that there may be a salty ocean underneath this jumbled, icy terrain. [more information]
It appears that the ocean lies beneath the surface somewhere in the outer 100 kilometers (60 miles), the approximate thickness of the ice/water layer, according to Kivelson, a researcher at the University of California, Los Angeles (UCLA).
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On previous Europa flybys, Galileo identified a magnetic north pole, but did not determine whether its position changes with time. "We wondered, 'Was it possible that the north pole did not move?' " Kivelson said.
Right: Two models consistent with images of Europa's surface include a subsurface layer of liquid water or perhaps warmer, convecting ice. Image credit: JPL and the SETI Institute. [more information]
It is not likely that the electric currents on Europa flow through solid surface ice, Kivelson explained, because ice is not a good carrier of currents. "But melted ice containing salts, like the sea water found on Earth, is a fairly good conductor," she said.
There is no other likely current-carrying material near Europa's surface, Kivelson added. "Currents could flow in partially melted ice beneath Europa's surface, but that makes little sense, since Europa is hotter toward its interior, so it's more likely the ice would melt completely. In addition, as you get deeper toward the interior, the strength of the current- generated magnetic field at the surface would decrease."
These latest findings are consistent with previous Galileo images and data showing a tortured surface seemingly formed when Europa's surface ice broke and rearranged itself while floating on a sea below. Further theoretical work is under way to analyze the fluid layer and its properties.
"It will be interesting to see whether this same type of phenomenon occurs at Jupiter's moon Ganymede," Kivelson said. Galileo is tentatively scheduled to fly by Ganymede twice this year.
Kivelson is joined in her magnetometer studies by Drs. Krishan Khurana, Christopher Russell, Raymond Walker, Christophe Zimmer, Martin Volwerk of UCLA, as well as Steven Joy and Joe Mafi, also of UCLA, and Dr. Carole Polanskey of NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
Additional information and pictures taken by Galileo are available at http://galileo.jpl.nasa.gov
Galileo has been orbiting Jupiter and its moons since December 1995, beaming to Earth unprecedented images and other information. JPL, a division of the California Institute of Technology, Pasadena, CA, manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
Galileo Mission Home Page -from NASA's Jet Propulsion Laboratory
Divining Water on Europa -Science@NASA feature story about the possibility of water on Jupiter's icy moon
Thursday's Classroom -educational lesson plans and classroom activities about Europa and life in extreme environments.