Transcript Discussion Notes from November 7th

Europa & Titan
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).
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.
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.
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.
Galileo’s 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.
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.
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).
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.
Life beneath the ice
•Ice cores from Lake Vostok reveal
traces of microbial life
•Included are cyanobacteria, bacteria,
fungi, spores, pollen grains, diatoms,
others
Future Europa Explorers
Titan
Determine Landing Site
Volcanism
Huygens Probe
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.'
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.
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.
Titan’s 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.
Methane
In this false color rendition, green light is the fluorescent emission of methane gas
powered by sunlight, at a wavelength of 3.3 microns…The 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.
What is the source of the Methane?
• Methane ocean?
• Cryovolcanism?
• Methanogens?