Evidence for 'Great Lake' On Europa....

[Doum]

Chance for an habitable ocean on Jupiter's moon Europa increase?

http://www.sciencedaily.com/releases/20 ... 132914.htm

[bystander]

Scientists Find Evidence for Subsurface 'Great Lake' on Europa
John Hopkins University | Applied Physics Laboratory | 2011 Nov 16

Nature Paper Details Potential New Habitat for Life on Jupiter's Icy Moon

[url=http://www.jhuapl.edu/newscenter/pressreleases/2011/111116_image1.asp][b][i]Europa's Great Lake[/i][/b][/url] - [i]Credit: Britney Schmidt/Dead Pixel FX/University of Texas[/i]

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In a finding of significance in the search for life beyond Earth, scientists have discovered what appears to be a body of liquid water the volume of the North American Great Lakes locked inside the icy shell of Jupiter's moon Europa—which could represent a new potential habitat for life.

Many more such lakes exist throughout the shallow regions of Europa's shell, the researchers predict in an online article for the journal Nature. Further increasing the potential for life, many of these lakes are covered by floating ice shelves that seem to be collapsing, providing a mechanism for transferring nutrients and energy between the surface and a vast ocean already thought to exist below the thick ice shell.

"The potential for exchange of material between the surface and subsurface is a big key for astrobiology," says Wes Patterson, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and a co-author of the study. "Europa's subsurface harbors much of what we believe is necessary for life but chemical nutrients found at the surface are likely vital for driving biology."

"One opinion in the scientific community has been, 'If the ice shell is thick, that's bad for biology—that it might mean the surface isn't communicating with the underlying ocean," adds Britney Schmidt, the paper's lead author and a postdoctoral fellow at The University of Texas at Austin's Institute for Geophysics. "Now we see evidence that it's a thick ice shell that can mix vigorously, and new evidence for giant shallow lakes. That could make Europa and its ocean more habitable."

The scientists focused on Galileo spacecraft images of two roughly circular, bumpy features on Europa's surface called chaos terrains. Based on similar processes seen here on Earth—on ice shelves and under glaciers overlaying volcanoes—they developed a four-step model to explain how the features form on Europa. It resolves several conflicting observations, some of which seemed to suggest that the ice shell is thick and others that it is thin.

While one of the chaos terrains appears to be fully formed, the other might still be forming—an indication that Europa's surface is still geologically active. "For quite some time, Europa geologists have been struggling figure out what these features are and how they form," says APL's Louise Prockter, a senior planetary scientist who has conducted numerous studies of Europa. "This is the first time that anyone has come up with an end-to-end model that explains what we see on the surface."

The scientists have good reason to believe their model is correct, based on observations of Europa from the Galileo spacecraft and of Earth. Still, because the inferred lakes are several kilometers below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell. Such a mission was rated as one of the highest priority flagship missions by the National Research Council's recent Planetary Science Decadal Survey and is currently being studied by NASA.

"If we're ever to send a landed mission to Europa, these areas would be great places to study," Prockter says.

Scientists Find Evidence for “Great Lake” on Europa and Potential New Habitat for Life
University of Texas, Austin | Institute for Geophysics | 2011 Nov 16

Click to play embedded YouTube video.

In a significant finding in the search for life beyond Earth, scientists from The University of Texas at Austin and elsewhere have discovered what appears to be a body of liquid water the volume of the North American Great Lakes locked inside the icy shell of Jupiter's moon Europa.

The water could represent a potential habitat for life, and many more such lakes might exist throughout the shallow regions of Europa's shell, lead author Britney Schmidt, a postdoctoral fellow at The University of Texas at Austin's Institute for Geophysics, writes in the journal Nature.

Further increasing the potential for life, the newly discovered lake is covered by floating ice shelves that seem to be collapsing, providing a mechanism for transferring nutrients and energy between the surface and a vast ocean already inferred to exist below the thick ice shell.

"One opinion in the scientific community has been, 'If the ice shell is thick, that's bad for biology — that it might mean the surface isn't communicating with the underlying ocean,'" said Schmidt. "Now we see evidence that even though the ice shell is thick, it can mix vigorously. That could make Europa and its ocean more habitable."

The scientists focused on Galileo spacecraft images of two roughly circular, bumpy features on Europa's surface called chaos terrains. Based on similar processes seen here on Earth — on ice shelves and under glaciers overlaying volcanoes — the researchers developed a four-step model to explain how the features form on Europa. It resolves several conflicting observations, some of which seemed to suggest that the ice shell is thick and others that it is thin.

"I read the paper and immediately thought, yes, that's it, that makes sense," said Robert Pappalardo, senior research scientist at NASA's Planetary Science Section who did not participate in the study. "It's the only convincing model that fits the full range of observations. To me, that says yes, that's the right answer."

The scientists have good reason to believe their model is correct, based on observations of Europa from the Galileo spacecraft and of Earth. Still, because the inferred lakes are several kilometers below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell. Such a mission was rated as the second-highest priority flagship mission by the National Research Council's recent Planetary Science Decadal Survey and is currently being studied by NASA. On Earth, radar instruments are used to image similar features within the ice, and are among the instruments being considered for a future Europa mission.

"This new understanding of processes on Europa would not have been possible without the foundation of the last 20 years of observations over Earth’s ice sheets and floating ice shelves," said Don Blankenship, a co-author and senior research scientist at the Institute for Geophysics, where he leads airborne radar studies of Earth’s ice sheets.

Schmidt and Blankenship's co-authors are Wes Patterson, planetary scientist at the Johns Hopkins University Applied Physics Laboratory, and Paul Schenk, planetary scientist at the Lunar and Planetary Institute in Houston.

Active formation of ‘chaos terrain’ over shallow subsurface water on Europa - B. E. Schmidt, D. D. Blankenship, G. W. Patterson, P. M. Schenk

• Nature (online 16 Nov 2011) DOI: 10.1038/nature10608

NASA Probe Data Show Liquid Water Evidence on Europa
NASA JPL-Caltech | 2011 Nov 16

Strange domes on Europa formed on thin ice
New Scientist | 2011 Nov 16

Life-Bearing Lake Possible on Icy Jupiter Moon
Discovery News | Irene Klotz | 2011 Nov 16

Europa’s Hidden Great Lakes May Harbor Life
Universe Today | Jason Major | 2011 Nov 16

Huge lakes of water may exist under Europa’s ice
Discover Blogs | Bad Astronomy | 2011 Nov 17

A Possible Subsurface Lake on Europa
Centauri Dreams | Paul Gilster | 2011 Nov 17

[neufer]

Click to play embedded YouTube video.

Is Europa's ice thin or thick? At chaos terrain, it's both!
The Planetary Society Blog
By Emily Lakdawalla : Nov. 17, 2011

<<Yesterday there was a press briefing about a paper published in Nature* about lakes inside Jupiter's moon Europa. I didn't have time to watch the briefing but I've just read the paper and it's a really important one. It's an academic paper, but in my opinion it also represents a detente in a long-running conflict.

Among Europa scientists there are two warring factions: the thick-icers and the thin-icers. (I know science isn't really supposed to work that way, but all too often, it does.) The question is how thick is the ice shell that overlies Europa's subsurface ocean (the existence of which pretty much everyone agrees on). The thin-icers claim that the water comes very, very close to the surface, sometimes even melting through. How else, they said, could you get a landscape that looks like icebergs floating in a frozen ocean?

Not so fast, say the thick-icers. No matter how much Europa's "chaos terrain" looks like icebergs floating in an ocean, physics makes that pretty much impossible. Europa's surface is directly exposed to space. Space is cold. Very cold. So cold that ice at Europa's distance from the Sun behaves, thermodynamically speaking, like rock does on Earth. On Earth, some lava gets through to the surface sometimes, but you never have hundreds of square kilometers of rock suddenly liquefying into lava at the surface, letting blocks of crust bob around like icebergs in a red-hot liquid rock lake. (Thankfully.) That's equivalent to what the thin-icers were saying happened from time to time on Europa.

In the decade since the ending of the Galileo mission, the thick-icers' mathematically rigorous arguments have pretty much carried the day. But the thin-icers haven't gone away, and the geophysicists have had a tough time trying to come up with an explanation for how Europa's chaos terrain forms that does make sense thermodynamically.

That's why this paper is important. Titled "Active formation of 'chaos terrain' over shallow subsurface water on Europa," it's a mathematically rigorous paper that describes a mechanism in which a thick-iced Europa can produce chaos terrain, without liquid water ever melting through to the surface. Europa's ocean remains at great depth, but there are perched "lakes" close to the surface, whose formation drives the creation of chaos. In a way, it's a bit of thin ice on top of a lot of thick ice.

The authors are Britney Schmidt, Don Blankenship, Wes Patterson, and Paul Schenk. Wes and Paul have done a lot of work mapping the icy moons and can describe in detail what chaos terrain looks like -- where it's high, where it's low, and so on. Paul has even made movie flyovers of Europa's chaos. Don Blankenship is a geophysicist who's done lots of fieldwork in Antarctica, studying how water melts and moves at the base of thick ice sheets, and who has applied that knowledge to Europa. And the first author, Britney Schmidt? She's a young scientist, a freshly minted Ph.D. in geophysics, who has, in this publication, fulfilled an ambition she'd formed as a 20-year-old undergrad: to become a scientist studying Europa when she grew up. And here she is, first author on a paper about Europa in the extremely prestigious journal Nature. Awesome. Here's a lengthy interview of Britney, in which she explains how she got there, and offers advice to young people who want to follow a path like hers.

Back to Europa. Here is the story that Britney and coauthors tell to explain how chaos forms (remember, geology is all about storytelling). I did my best to translate the story, but it can be kind of hard to explain why ice can move around while thoroughly solid and why it melts at some times and not at others. If you don't follow me, that's OK, just skip past the image caption, and I'll explain why their story is a good one.

Credit: Nature Magazine

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[b][color=#FF0000][size=150]Thrace Macula, Europa[/size][/color][/b]

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[list]Diagram explaining formation of Europa chaos [/list]
How Europa's chaos terrain is made, in sketch form. In (a), a plume of warm ice (not liquid water, but a solid ice plume, like the rocky plumes in Earth's mantle) rises upward. Above the upwelling plume, the surface might (but might not) warp upward. At great depth in Europa's crust, the pressure of the overlying ice overcomes the relatively warm temperatures to keep ice in solid form. On to (b): when the upwelling plume of warm ice pushes the nearer-surface ice upward, this balance is disturbed, and ice within the crust at a few kilometers below the surface begins to "sweat," partially melting. Liquid water is slightly denser than frozen ice, so takes up less volume. The reduced volume means that over the area of the melting, the surface sinks downward. The thicker crust at the edge of the downwarped area produces higher pressure on the liquid melt than the thinner crust at the center, so as more of the crust melts, the water flows from high pressure toward low pressure, producing a "lens" of water, thickest in the center and thinnest at the edges, and the melting water is pinned in a confined area above the uprising plume. Then comes (c): As the "lid" over the plume sinks downward, it also bends, and cracks open in the bottom of the lid to accommodate that bending. Briny liquid from the lake, under pressure from above, squirts into these cracks and percolates into the porous granular ice in the crust. In this way the crust never melts through but it is saturated with water, and large chunks of of crust can "calve" off as the fissures crack. If the blocks are narrow, they may tilt sideways. Finally, in (d), as the geologic activity subsides and the lens of liquid water refreezes, so does the water saturating the crust. Freezing water expands, so the brine-wetted matrix material in between the calved blocks domes upward. [/color]

Why is this story better than any other I've heard? Because it explains a lot of the descriptive evidence that geologists like Wes and Paul have assembled over years of work. Among other things, the story explains:

• Europan terrains like Conamara Chaos and Thrace Macula are approximately circular.
  
  They contain what appear to be floating blocks calved off of the adjacent crust, stuck in a "matrix" of disrupted, darkened material.
  
  But Conamara Chaos stands higher than the surrounding crust and also has matrix domes between its blocks, while Thrace Macula is sunken below the adjacent crust.

But this isn't just a story. It is, in fact, a scientific theory that makes testable predictions. It suggests that Conamara is a relatively old chaos, where there may once have been a lake but now it's all frozen. By contrast, at low-lying Thrace Macula, we're seeing chaos in the middle of this formation process. Britney and her coauthors wrote:

At Thrace Macula, we are probably witnessing active chaos formation....[the evidence] indicates that the lens below Thera Macula was liquid at the time of the Galileo encounter. Today, a melt lens of 20,000-60,000 cubic kilometers of liquid water probably lies below Thera Macula; this equates to at least the estimated combined volume of the Great Lakes....Thera Macula may have noticeable changes between the Galileo encounter and the present day.

So for all of you people who were secretly hoping the thin-icers would win the argument because you are hoping to see humans send a probe onto Europa's surface and maybe even drill through the ice to its ocean, you have a consolation prize. The ocean's still deep below the surface, 10 to 20 kilometers, but if Britney and her coworkers are right, there very likely are liquid water lakes at only maybe 3 kilometers' depth. And water from those lakes has squirted upward, helping wet and break up Europa's crust all the way to the surface. The dark stains associated with chaos could well be the salts and other stuff that are dissolved in that lake water. So, land at Thera, and you might be able to taste Europa's ocean!>>

[Ann]

I am so very much a Jennie-come-lately to this topic, but I must say that it sounds very interesting. To me, Europa is a lot more interesting than Saturn's moon Titan, because the liquid on - or in! - Europa is water, while on Titan the liquid is methane, or something like that. Admittedly I think that Enceladus is even more interesting than Europa, but Europa is about half as far away, and a trip to Europa is therefore more affordable than a trip to Enceladus.

The idea that some of these roundish shapes could be ice-covered lakes, covered by relatively thin ice, actually sounds plausible to me. It is also interesting that they are a different color than the otherwise relatively white ice of Europa. The idea that comes to mind is that the liquid water underneath might contain organic compounds that give the water an orange cast.

The possibility that there might be liquid lakes on Europa makes this moon every bit as interesting as Mars to me.

Ann