Galileo buzzes Europa
On Sunday Galileo executed a close flyby of Europa
for the last time during the current mission.
Right: Artist Duane Hilton's concept of Galileo as it flies by Europa on Jan. 31, 1999.
This latest flyby is the last of a series that began in late-1997 as part of the extended Galileo-Europa Mission (GEM). Scientists are intrigued by Europa because of mounting evidence that a liquid ocean exists beneath its frozen surface. Although the moon's surface temperature is a chilly -260° F 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.
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A geologically older, smoother surface, bluish in tone, underlies the ridge system. The blue surface is composed of almost pure water ice, whereas the composition of the dark, brownish spots and ridges is not certain. One possibility is that they contain mineral salts in a matrix of high water content.
Surf's up on Europa
Galileo will continue to study Europa from a distance during the second half of the Galileo Europa Mission, but no additional close flybys are planned. However, NASA scientists have several projects in the planning stages to explore Europa from close range.
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.
Another intriguing proposal is the Europa Ice Clipper. The Ice Clipper is a flyby mission designed to obtain samples of Europa's surface by dropping hollow copper spheres onto the icy surface of the moon. After dropping the 10 kg spheres, the spacecraft would swing around and fly through the plume of surface material created by the impact. Surface debris would be captured by an aerogel collector similar to the one that will used by the Stardust spacecraft to capture particles from a comet. Like Stardust, the Ice Clipper would return its samples to Earth for analysis. (Editor's note: Stardust is scheduled for launch on Feb. 6, 1999. It will rendevous with Comet Wild-2 in the year 2004.)
Other missions on the drawing board include Icepick, the Europa Ocean Observer, and the Europa Lander. So far only the Europa Orbiter has been funded. It will serve as an important precursor to future missions to Jupiter's enigmatic moon.
Above: These images reveal the dramatic
topography of Europa's icy crust. North is to the right. An east-west
running double ridge with a deep intervening trough cuts across
older background plains. The numerous cracks and bands may indicate
where the crust has pulled apart and sometimes allowed dark material
from beneath the surface to well up. A computer generated three
dimensional perspective shows that bright material, probably
pure water ice, prevails at the ridge crests and slopes while
most dark material is confined to lower areas such as valley
information from the Planetary Photojournal.
Galileo Europa Mission status - Feb. 1, 1999, from JPL
Galileo Europa Mission status - Jan. 27, 1999, from JPL
Evidence for slush beneath the surface of Europa - from JPL and Brown University
Galileo home page at JPL, with the latest on Europa
Jet Propulsion Laboratory home page
NASA Office of Space Science - news and research
3 Dec. 1998 The frosty plains of Europa
22 Oct. 1998 Callisto makes a big splash
02 Oct. 1998 Galileo gets a close-up view of mysterious Europa
12 March 1998 Exotic-looking microbes turn up in ancient Antarctic ice
13 March 1998 Space Tether may be best way to explore Europa
05 March 1998: Clues to possible life on Europa may lie buried in Antarctic ice
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