Europa: Sea Salts or Battery Acid? [Image and caption]

Source image: GIF (171K) TIF (687K)

This composite image of the Jupiter-facing hemisphere of
Europa was obtained on November 25, 1999 by two instruments
onboard NASA’s Galileo spacecraft. The global black-and-white
view, by the spacecraft’s camera, provides the highest resolution
view ever obtained of this side of Europa. The superimposed
false-color image, obtained by Galileo’s near-infrared mapping
spectrometer instrument, reveals the presence of materials with
differing compositions on Europa’s surface.

In this image, blue areas represent the cleanest, brightest
icy surfaces, while the reddest areas have the highest
concentrations of darker, non-ice materials. The mixture of
colors seen here is most likely the result of both variations in
the ages and composition of surface materials. The dark
materials are believed to fade with the passage of time.

This area is highly unusual compared to many other areas on
Europa because of its high concentration of fresh-appearing
bright ridges and fractures. On other parts of Europa, the
darker areas appear to be the most recently formed, but here the
ridges and fractures appear to “overprint” the underlying darker
mottled terrain.

Scientists disagree about the chemical makeup of the dark
materials; both sulfuric acid (common battery acid) and salty
minerals, perhaps from a subsurface ocean, have been suggested.
Analysis of images like this one may help to resolve this
controversy. Surprisingly, either material could help to produce
conditions below the surface that could be favorable to the
formation of living organisms.

The colored area is centered near the intersection of the
equator and the Europan “prime meridian,” where the longitude is
assigned the value of 0 degrees. This is the sub-Jupiter point,
where Jupiter always appears to be almost directly overhead.
This phenomenon occurs because Europa takes the same period of
time to rotate as it does to orbit around Jupiter (3.55 days).
The area imaged in color is about 400 by 400 kilometers (250 by
250 miles), an area of about 160,000 square kilometers (about
62,000 square miles).

The Jet Propulsion Laboratory, Pasadena, CA manages the
Galileo mission for NASA’s Office of Space Science, Washington,
DC. JPL is a division of the California Institute of Technology,
Pasadena, CA.

This image and other images and data received from Galileo
are posted on the Galileo mission home page at
http://galileo.jpl.nasa.gov . Background information and
educational context for the images can be found at
http://galileo.jpl.nasa.gov/images/io/ioimages.html .

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