Galileo takes a close look at icy Europa
Marshal Space Flight Center Space Science News
The spacecraft flew within 2300 miles of the mysterious satellite last weekend.
2 October, 1998: NASA's Jet Propulsion Laboratory reports that the Galileo
spacecraft completed its closest-ever flyby of Europa on schedule and on
target. On Friday, Sept. 25, at 8:54 p.m. PDT, Galileo skimmed over the icy
moon at an altitude of only 2,226 miles.
The flyby was performed in cruise mode without Galileo's gyroscopes, because
the gyros activated a fault protection program last Thursday, Sept. 24. The
on board star scanner was used instead as the primary reference for
determining the spacecraft's orientation in space. Nevertheless, the flyby
was considered a success.
Europa is one of the most intriguing bodies in the solar system because
scientists are increasingly confident that it harbors a deep, underground
ocean of liquid water. Europa's icy surface has intrigued scientists ever
since the Voyager spacecraft missions flew through the Jupiter system in
1979. At -260 degrees F, the moon's surface temperature could deep-freeze an ocean over several million years, but it's possible that warmth from a tidal tug
of war with Jupiter and neighboring moons could be keeping large parts of
Europa's ocean liquid. Tidal friction from Jupiter is also thought to be
responsible for volcanic activity on Europa's neighbor Io.
Images of Europa from the Galileo spacecraft reveal a complicated terrain of
grooved linear ridges and crustal plates which seem to have broken apart and
rafted into new positions. That could indicate subsurface water or slush. In
the image above, blue tints represent relatively old ice surfaces while
reddish regions may contain material from more recent internal plore
Europa. One is the Europa Orbiter. It would use a radar sounder to study
Europa's icy surface and attempt to determine the thickness of the ice and
whether liquid water exists below the ice. Other instruments to study the
surface and interior would include an imaging device with multiple filters
to map the surface at a resolution of 100 meters and an altimeter to measure
the topography and characterize the tidal response of the surface. The
mission could launch in 2003 and would serve as a precursor to spacecraft
that would actually send undersea explorers into the Europan oceans.
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