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Topic Name: New research brings scientists closer to explore Jupiter’s moon Europa tantalizing ice-covered ocean
Category: Environmental engineering
Research persons: William McKinnon, Donald Blankenship, Peter Doran
Location: Washington University, St. Louis, United States
Details
Jupiter’s moon Europa is just as far away as ever, but new research is
bringing scientists closer to being able to explore its tantalizing ice-covered
ocean and determine its potential for harboring life.
“We’ve learned a lot about Europa in the past few years,” says William
McKinnon, professor of Earth and Planetary Sciences at Washington
University in St. Louis, Mo.
“Before we were almost sure that there was an ocean, but now the scientific
community has come to a consensus that there most certainly is an ocean. We’re
ready to take the next step and explore that ocean and the ice shell that
overlays it. We have a number of new discoveries and techniques that can help us
do that.”
McKinnon is discussing some of these recent findings and new opportunities
for exploring Europa in a news briefing at the meeting of the American
Geophysical Union in San Francisco. He is joined by colleagues Donald
Blankenship, research scientist at the Institute for Geophysics at the University
of Texas at Austin’s Jackson School of Geosciences., and Peter
Doran, associate professor of Earth and Environmental Sciences, University
of Illinois at Chicago.
McKinnon points to refined methods that can use combined measurements of
gravity and the magnetic
field made from orbit to characterize Europa's ocean. By observing how the
moon flexes and deforms and by measuring magnetic variations, researchers can
determine how thick or thin the ice is over the ocean and even learn how salty
the ocean is. A new model shows that radiation on Europa is much less, up to
two-thirds less, than previous models predicted, making the environment much
more hospitable for orbiting spacecraft or landers to operate.
Sophisticated reprocessing of data from the Galileo mission has revealed new
information about the chemistry of Europa’s surface. It maps the presence of
carbon dioxide, an important chemical for life, most probably coming from the
ocean beneath the surface. This indicates that improved measurements from orbit
have the chance to detect compounds not found in the Galileo data.
Future explorations of Europa will benefit from lessons learned from the
Cassini spacecraft’s recent findings of active geysers on Saturn’s moon
Enceladus. “Europa is a young, geologically active body like Enceladus,”
says McKinnon. Galileo didn’t see any plumes on Europa like those spouting
from Enceladus, but it didn’t have the best instrumentation to detect the
telltale hot spots. “Now we know what we should look for,” says McKinnon,
“and we should expect the unexpected.”
New radar sounding techniques will be a key component for exploring Europa.
“There have been theories about whether the ice above the ocean is thick or
thin, and now we have the ability to determine this with radar,” says
Blankenship. “That’s been proved by the radar on Mars Express, which imaged
the north polar cap of Mars, and the higher-resolution radar on the Mars
Reconnaissance Orbiter. Radar can give us a detailed cross section through the
ice shell on Europa.” The ice-penetrating radar will also be able to locate
liquid water both within and beneath the shell, he continues, just as it can
spot water within crevasses and lakes beneath the ice of Antarctica. "Free
water within the icy shell and its relationship to the underlying ocean will be
a critical factor in determining the habitability of Europa."
Researchers are also preparing for the day in the future when they will be
able to get to Europa's surface and ultimately into its ocean to explore it
directly. "In the meantime, we're using extreme environments on Earth as
our laboratory," says Doran. "Ice-covered lakes in Antarctica are
good, small-scale analogs to what we might find on Europa." Doran is lead
investigator of a project called Endurance, which, in collaboration with Stone
Aerospace, is developing an autonomous underwater robotic vehicle, to test
approaches and procedures for exploring Europa's ocean. The project is funded by
NASA's Astrobiology Science and Technology for Exploring Planets program.
"We're testing the vehicle in Wisconsin in February 2008," Doran
says, "and then we'll be deploying it in Antarctica later in the
year." The robotic explorer will be able to create three-dimensional maps
of the subsurface Antarctic lake. It will also be able to map the biochemistry
of the water body, pinpointing the chemical signatures that may indicate life.
For Europa, under-ice exploration lies in the distant future. In the
meantime, say the researchers, a closer look at Europa is possible from an
orbiting spacecraft able to measure gravity and magnetic fields, determine
surface composition, search for active or recent eruptions, and use radar to
understand the relationship between the surface and the sub-surface.
In figure 1, Thick or thin ice shell on Jupiter’s moon Europa? Scientists are all but certain that Europa has an ocean underneath its surface ice, but do not know how thick this ice might be. This artists’ conception illustrates two possible cut-away views through Europa’s ice shell. In both heat escapes, possibly volcanically, from Europa’s rocky mantle and is carried upward by buoyant oceanic currents. If the heat from below is intense and the ice shell is thin enough (left), the ice shell can directly melt, causing what are called “chaos” on Europa, regions of what appear to be broken, rotated, and tilted ice blocks. On the other hand, if the ice shell is sufficiently thick (right), the less intense interior heat will be transferred to the warmer ice at the bottom of the shell, and additional heat is generated by tidal squeezing of the warmer ice. This warmer ice will slowly rise, flowing as glaciers do on Earth, and the slow but steady motion may also disrupt the extremely cold, brittle ice at the surface. Europa is no larger than Earth’s moon, and its internal heating stems from its eccentric orbit about Jupiter, seen in the distance. As tides raised by Jupiter in Europa’s ocean rise and fall, they may cause cracking, additional heating, and even venting of water vapor into the airless sky above Europa’s icy surface.
In figure 2, Byrd Glacier, Antarctica. Exploration on Earth of analogs to Europa's ice-covered ocean will be critical steps toward launching an exploration of Europa. Antarctica's ice-covered lakes will offer testing grounds for an array of technologies that could prove useful in space.
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