archive: SETI Galileo shows closeup view of Europa fault

SETI Galileo shows closeup view of Europa fault

Larry Klaes ( )
Wed, 09 Dec 1998 09:26:33 -0500

>Date: Mon, 7 Dec 1998 12:25:22 -0800 (PST)
>From: JPL Media Relations Office <>
>Subject: Galileo shows closeup view of Europa fault
>PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
>Contact: Jane Platt
> New pictures from NASA's Galileo spacecraft show a closeup
>view of a fault, or fracture, on Jupiter's icy moon Europa that
>stretches as long as the California segment of the infamous San
>Andreas fault.
> The Europan fault, known as Astypalaea Linea (pronounced
>ast-ipp-uh-LAY-uh LINN-ee-uh) was first discovered in 1996 when
>Dr. Randy Tufts, Galileo imaging team affiliate and research
>associate at the University of Arizona, Tucson, AZ, reviewed
>distant images taken years earlier by NASA's Voyager spacecraft.
>The new mosaic of Galileo images released today captures a 290-
>kilometer-long (180-mile) portion of the fault in Europa's icy
>surface. Scientists calculate its full length at about 810
>kilometers (more than 500 miles), about the same distance as the
>part of the San Andreas fault that runs from the
>California-Mexico border north to the San Francisco Bay.
> "Comparisons between this Europan fault and faults on Earth
>may generate ideas we can use in studying earth movements here on
>our planet," said Tufts. "In addition, Astypalaea Linea is
>simply a beautiful structure."
> The new Galileo images show that about 50 kilometers (more
>than 30 miles) of movement, or "displacement," has taken place
>along the fault, which is located near Europa's South Pole.
>Bends in the fault have allowed the surface to be pulled apart as
>this movement took place along Astypalaea Linea, which is the
>largest known strike-slip fault on Europa and one of the largest
>strike-slip faults known to exist anywhere. A strike-slip fault
>is one in which two crustal blocks move horizontally past one
>another, somewhat like two opposing traffic lanes.
> This pulling-apart along the fault's bends created openings
>through which warmer, softer ice from below Europa's brittle ice
>shell surface, or frozen water from a possible subsurface ocean,
>could reach the surface. This upwelling of material formed large
>areas of new ice within the boundaries of the original fault. A
>similar pulling-apart phenomenon can be observed in the
>geological trough surrounding California's Salton Sea, and in
>Death Valley and the Dead Sea. However, in those cases, the
>pulled-apart regions can include upwelled materials, but may be
>mostly composed of sedimentary and erosional material deposited
>from above.
> Tufts believes Astypalaea Linea is probably no longer
>active, because large ridges formed more recently crosscut it
>without interruption. Opposite sides of the fault can be
>reconstructed in puzzle-like fashion, matching the shape of its
>sides as well as individual older lined areas that had been
>broken by its movements. The overall motion along the fault seems
>to have followed a continuous narrow break along the entire
>length of the feature, with a path resembling steps on a
>staircase crossing the pulled-apart zones. Between the zones,
>this break coincides with ridges that separate them.
> Tufts and fellow University of Arizona researchers, in a
>group led by Dr. Richard Greenberg, suspect that the fault motion
>is induced by the pull of variable daily tides generated by
>Jupiter's gravitational tug on Europa's icy crust. This tidal
>effect produces a phenomenon they call "walking."
> "In walking, tidal tension opens the fault, subsequent tidal
>stress causes it to move lengthwise in one direction, and then
>the tidal forces close the fault up again. This prevents the
>area from moving back to its original position; it may move
>forward with the next daily tidal cycle," Tufts explained. "The
>walking analogy describes perfectly what we think happens at the
>fault, resulting in a steady accumulation of these lengthwise
>offset motions. Walking may explain the appearance of many other
>faults and areas of cracks and ridges on Europa."
> Unlike Europa, here on Earth, large strike-slip faults such
>as the San Andreas are set in motion by plate tectonic forces
>from the planet's mantle. Based on the Europa findings, Tufts
>said, "The data may teach us more about the detailed structure
>that develops at bends in Earth's faults, including the San
> The latest Galileo images of Astypalaea Linea are available
>on the Internet at the following websites:
> Galileo has been in orbit around Jupiter and its moons for
>the past three years. Its primary mission ended in December 1997,
>and the spacecraft is currently in the midst of a two-year
>extension known as the Galileo Europa Mission. Galileo is managed
>by JPL for NASA's Office of Space Science, Washington, DC. JPL
>is a division of Caltech, Pasadena, CA.
> For information about animation of Astypalaea Linea, contact
>the JPL Media Relations Office at (818) 354-5011.
> #####
>JP 98117
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