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Vast Liquid Ocean Beneath Europa
Is Connected With The Moon's Frozen Exterior

5 March, 2013

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MessageToEagle.com - The scientists analyzed the data from W. M. Keck Observatory, the world's two largest optical/infrared telescopes located on the summit of Mauna Kea on the Big Island of Hawaii and found the strongest evidence yet that salty water from the vast liquid ocean beneath Europa’s frozen exterior actually makes its way to the surface.

There is a chemical exchange between the ocean and surface, making the ocean a richer chemical environment, and implies that learning more about the ocean could be as simple as analyzing the moon’s surface, say Mike Brown, California Institute of Technology (Caltech) astronomer and Kevin Hand, an astrobiologist and planetary scientist from the Jet Propulsion Laboratory (JPL).



Click on image to enlarge

Based on new data from the W. M. Keck Observatory about Jupiter's moon Europa, astronomers hypothesize that chloride salts bubble up from the icy moon's global liquid ocean and reach the frozen surface where they are bombarded with sulfur from volcanoes on Jupiter's largest moon, Io. This illustration of Europa (foreground), Jupiter (right) and Io (middle) is an artist's concept. Credit: NASA/JPL-Caltech


“We now have the best spectrum of this thing in the world,” Brown says. “Nobody knew there was this little dip in the spectrum because no one had the resolution to zoom in on it before.”

“We now have evidence that Europa’s ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals,” says Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy at Caltech.

“That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”

“The surface ice is providing us a window into that potentially habitable ocean below,” says Hand, deputy chief scientist for solar system exploration at JPL.

Since the days of the Galileo mission, when the spacecraft showed that Europa was covered with an icy shell, scientists have debated the composition of Europa’s surface. The infrared spectrometer aboard Galileo was not capable of providing the detail needed to definitively identify some of the materials present on the surface.

Now, using current technology on ground-based telescopes, Brown and Hand have definitively identified a spectroscopic feature on Europa’s surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite, that could only originate from the ocean below.

“Magnesium should not be on the surface of Europa unless it’s coming from the ocean,” Brown says. “So that means ocean water gets onto the surface, and stuff on the surface presumably gets into the ocean water.”

Europa’s ocean is thought to be 100 kilometers deep and covers the entire globe. The moon remains locked in relation to Jupiter, with the same hemisphere always leading and the other trailing in its orbit. The leading hemisphere has a yellowish appearance, while the trailing hemisphere seems to be splattered and streaked with a red material.


Model of Europa's interior. The moon is thought to have a metallic core surrounded by a rocky interior, and then a global ocean on top of that surrounded by a shell of water ice. Credit: NASA


The spectroscopic data from that red side has been a cause of scientific debate for 15 years. It is thought that one of Jupiter’s largest moons, Io, spews volcanic sulfur from its atmosphere, and Jupiter’s strong magnetic field sends some of that sulfur hurtling toward the trailing hemisphere of Europa, where it sticks. It was also clear from Galileo’s data that there is something other than pure water ice on the trailing hemisphere’s surface. The debate has focused on what that other something is—i.e., what has caused the spectroscopic data to deviate from the signature of pure water ice.

“From Galileo’s spectra, people knew something was there besides water. They argued for years over what it might be—sodium sulfate, hydrogen sulfate, sodium hydrogen carbonate, all these things that look more or less similar in this range of the spectrum,” says Brown. “But the really difficult thing was that the spectrometer on the Galileo spacecraft was just too coarse.”

Using the Keck II telescope on Mauna Kea, Brown and Hand first mapped the distribution of pure water ice versus anything else on the moon. The spectra showed that even Europa’s leading hemisphere contains significant amounts of nonwater ice.

Then, at low latitudes on the trailing hemisphere—the area with the greatest concentration of the nonwater ice material—they found a tiny dip in the spectrum that had never been detected before.

The two researchers racked their brains to come up with materials that might explain the new spectroscopic feature, and then tested everything from sodium chloride to Drano in Hand’s lab at JPL, where he tries to simulate the environments found on various icy worlds.

“We tried to think outside the box to consider all sorts of other possibilities, but at the end of the day, the magnesium sulfate persisted,” Hand says.

Now, Brown and Hand believe that the composition of Europa’s sea closely resembles the salty ocean of Earth.

“If you could go swim down in the ocean of Europa and taste it, it would just taste like normal old salt,” he says.

“If we’ve learned anything about life on Earth, it’s that where there’s liquid water, there’s generally life,” Hand says. “And of course our ocean is a nice salty ocean. Perhaps Europa’s salty ocean is also a wonderful place for life.”

The work is described in a paper that has been accepted for publication in the Astronomical Journal.

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