Europa

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Europa Titan
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NIMS Instrument on Galileo
For the three large icy Galilean satellites,
Callisto, Ganymede, and Europa, the primary NIMS
science objectives are to map the various surface
compositional units and to identify their
elemental and mineralogical composition. A
primary question concerning these units is the
composition of the dark components that are mixed
with the dominant water-ice crusts. Are these
materials silicates or organic-rich materials
derived from primitive objects such as comet
nuclei? If silicates, NIMS may detect bands due
to olivines, pyroxenes, or a range of
iron-bearing minerals. C-H features might be
present if the satellite surfaces contain dark
organic components such as those found on some
asteroids. Magnetospheric sources of implanted
material (e.g. sulfur) may be an important
process, providing chemically reactive species
which can modify the surfaces (e.g. generating
S-O from the S implanted in H2O).
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View of a small region of the thin, disrupted,
ice crust in the Conamara region of Jupiter's
moon Europa showing the interplay of surface
color with ice structures. The white and blue
colors outline areas that have been blanketed by
a fine dust of ice particles ejected at the time
of formation of the large (26 kilometer in
diameter) crater Pwyll some 1000 kilometers to
the south. A few small craters of less than 500
meters or 547 yards in diameter can be seen
associated with these regions. These were
probably formed, at the same time as the
blanketing occurred, by large, intact, blocks of
ice thrown up in the impact explosion that formed
Pwyll.
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A color-enhanced close-up of Europa's surface.
Areas of blue are thought to be pure water ice.
The "cryo-volcanic" ridges have a brown color
showing where mineral-laden water from
underground appears to have percolated to the
surface through cracks in the crust.
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Thera and Thrace are two dark, reddish regions of
enigmatic terrain that disrupt the older icy
ridged plains on Europa. One model for the
formation of these and other chaos regions on
Europa is complete melt-through of Europa's icy
shell from an ocean below. Another model is that
warm ice welled up from below and caused partial
melting and disruption of the surface.
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Galileos Magnetometer
The Jovian magnetosphere envelopes the planet in
a vast cocoon that extends more than seven
million kilometers from the planet in all
directions and deflects the solar wind in its
outward flow from the Sun. The gargantuan scale
of the system is readily understood as arising
from a combination of factors the low dynamic
pressure of the solar wind at the orbit of
Jupiter, down by a factor of more than 25 from
its level at 1 AU the large planetary radius, 11
times that of the Earth the strong dipole
magnetic moment of the planet, more than four
orders of magnitude larger than that of the
Earth and the existence of a relatively dense,
centrifugally accelerated plasma that acts to
inflate the magnetosphere from within.
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From Khurana et al. 1998
Initial results from the spacecraft's
magnetometer1,2 have indicated that neither
Europa nor Callisto have an appreciable internal
magnetic field, in contrast to Ganymede3 and
possibly Io4. Here we report perturbations of the
external magnetic fields (associated with
Jupiter's inner magnetosphere) in the vicinity of
both Europa and Callisto. We interpret these
perturbations as arising from induced magnetic
fields, generated by the moons in response to the
periodically varying plasma environment.
Electromagnetic induction requires eddy currents
to flow within the moons, and our calculations
show that the most probable explanation is that
there are layers of significant electrical
conductivity just beneath the surfaces of both
moons. We argue that these conducting layers may
best be explained by the presence of salty
liquid-water oceans, for which there is already
indirect geological evidence5,6 in the case of
Europa.
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These artist's drawings depict two proposed
models of the subsurface structure of Europa.
Geologic features on the surface, imaged by the
Solid State Imaging (SSI) system on NASA's
Galileo spacecraft might be explained either by
the existence of a warm, convecting ice layer,
located several kilometers below a cold, brittle
surface ice crust (top model), or by a layer of
liquid water with a possible depth of more than
100 kilometers(bottom model). If a 100 kilometer
(60 mile) deep ocean existed below a 15 kilometer
(10 mile) thick Europan ice crust, it would be 10
times deeper than any ocean on Earth and would
contain twice as much water as Earth's oceans and
rivers combined. Unlike the Earth, magnesium
sulfate might be a major salt component of
Europa's water or ice, while the Earth's oceans
are salty due to sodium chloride (common salt).
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Analog sites on Earth
In 1974, a team of scientists conducting airborne
research passed over the Soviet research station
Vostok in Antarctica. Their sounding instruments
detected an expanse of water beneath the ice
roughly the size of Lake Ontario. Although
Antarctica records some of the coldest
temperatures on Earth, Lake Vostok is buried
under four kilometers of ice. The ice sheet acts
as a blanket, shielding the lake from cold
temperatures on the surface. It is also thought
that geothermal heat helps keep the water liquid.
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Life beneath the ice

• Ice cores from Lake Vostok reveal traces of
  microbial life
• Included are cyanobacteria, bacteria, fungi,
  spores, pollen grains, diatoms, others

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Future Europa Explorers
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Titan
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Determine Landing Site
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Volcanism
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Huygens Probe
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A bright linear feature suggests an area where
water ice may have been extruded onto the
surface. Also visible are short, stubby dark
channels that may have been formed by 'springs'
of liquid methane rather than methane 'rain.'
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The left-hand side shows a boundary between light
and dark areas. The white streaks seen near this
boundary could be ground 'fog,' as they were not
immediately visible from higher altitudes.
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The surface is darker than originally expected,
consisting of a mixture of water and hydrocarbon
ice. There is also evidence of erosion at the
base of these objects, indicating possible
fluvial activity.
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Titans Atmosphere

• 1.5 bars
• N2 and Methane
• Methane photodissociates in 107 years once in the
  atmosphere. Something must replenish it!

This graph shows data acquired by Cassini as it
flew by Titan at an altitude of 1,200 kilometers
(745 miles) on Oct. 26, 2004 - its closet
approach yet to the hazy moon. The data is from
Cassini's ion and neutral mass spectrometer,
which detects charged and neutral particles in
the atmosphere. The graph reveals a diversity of
hydrocarbons in the high atmosphere above Titan,
including benzene and diacetylene.
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Methane
In this false color rendition, green light is the
fluorescent emission of methane gas powered by
sunlight, at a wavelength of 3.3 micronsThe glow
extends over 700 kilometers (435 miles) above the
surface, revealing the unusual thickness of the
moon's atmosphere, which nearly doubles Titan's
volume compared to the volume of the solid
sphere, indicated by the solid line. On the
nightside (right side), the moon glows red out
for over 200 kilometers (125 miles) altitude,
indicating carbon-monoxide emission at 4.7 micron
wavelength produced in Titan's relatively warm
stratosphere.
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What is the source of the Methane?

• Methane ocean?
• Cryovolcanism?
• Methanogens?