From
"http://www.astronomy.com/Content/Dynamic/Articles/000/000/001/738lbwsc.asp";
-- probably nothing you don't already know... Go to
the link to see an artistr's concept of the JIMO
spacecraft approaching Jupiter.
----
Heading back to Jupiter’s moons
NASA has started planning an ambitious mission to
orbit Europa, Ganymede, and Callisto.
by Richard Talcott
When NASA crashed the Galileo spacecraft into Jupiter
in September 2003 (see “The long goodbye,” Astronomy,
October 2003), it marked the end of a spectacular
eight-year mission that provided strong evidence that
oceans exist under the icy crust of three of the
Galilean moons. Galileo already had far exceeded its
design lifetime, but that doesn’t mean NASA has
nothing left to explore.
To continue the exploration of Jupiter’s water worlds,
NASA is thinking about the Jupiter Icy Moons Orbiter
(JIMO). This sophisticated spacecraft would orbit
Europa, Ganymede, and Callisto to investigate their
makeup, their history, and their potential for
sustaining life.
Galileo discovered that all of Jupiter’s large icy
moons appear to have the three ingredients considered
essential for life: water, energy, and the necessary
chemical contents. Galileo’s evidence suggests that
liquid water has reached Europa’s surface in
geologically recent times, and it still may lie
relatively close to the surface. Closer observations
of Callisto and Ganymede would provide key comparisons
for understanding the evolution of all three moons.
Current plans call for JIMO to use electric propulsion
powered by a nuclear fission reactor. This would raise
the technology bar for NASA, making it possible to
conduct a realistic mission to orbit all three moons
one after the other. Just as important, it also would
open the rest of the outer solar system to detailed
exploration in later missions.
The spacecraft would spend many months spiraling
toward each moon, at least one full month in orbit,
and another several months spiraling away before
heading to its next target. Detailed observations
would be made throughout this extended period, but the
highest quality observations would come during the
low-altitude, high-inclination orbit of each moon.
JIMO scientists have set three major goals for the
mission. First, they want to study the oceans:
verifying their existence, finding their locations
within the moons, studying the structure of their icy
crusts, and assessing the internal processes that keep
the oceans liquid. Second, they want to study the
possible role of the oceans in astrobiology:
determining the types of volatile substances and
organic compounds on and near the surfaces, and
understanding the processes involved in their
formation and modification. And third, they want to
investigate interactions within the jovian system:
studying the atmospheres of the satellites as well as
the interactions among Jupiter and the surfaces and
interiors of its satellites.
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