During the E15 encounter, Galileo accquired the first segments of two massive hemispheric transects. 15ESREGMAP01, on the antijovian side, covers a large area within the famous G1 false color image showing the intersection of Minos and Udaeus Lineae. Presented here is an approximate natural color version along with a comparison with NASA's beautiful and oft-reproduced false color release from 1998:

15ESREGMAP01 greyscale

Color version

3-panel comparison

Cropped scenes of several features are in the wallpapers directory of the FTP site

The area to the north of the E15 mosaic was imaged in January 1999 during the E19 encounter. Also covered by G1 color data, this observation included a second, slightly closer look for stereo imaging as well.

19ESNORLAT01 greyscale

19ESNORPLN01 greyscale

3-panel color comparison

Phenomenal imagery. I found my favorite 1024x768 patch to use as a screensaver.

OMG - those mosaics are incredible !!!

Stunning images, Orion!
Can you tell us which bands/filters you used in the color panels?

The color images used for the "natural" mosaics in the first two posts were IR-7560 (assigned the 649nm red filter's rough values of r255/g0/b0), the 559nm green (r127/g255/b0), and the 404nm violet (r6/g0/b255). The composited image was visually tweaked to produce an approximation of the muddy reddish browns, salmon hues, and yellows shown in LPL/ASU products of the same region. The cropped color image was cut into 12 sections, rendered at 20% opacity, and visually aligned in peices over the mosaic, with overlapping seams carefully blended. Saturation was then increased, and the layered image flattened. The false color version of the E15 mosaic is the NASA/JPL release. The false color version of the E19 mosaic is the original 1996 G1 false color image, rendered transparent and positioned over the mosaic with the same technique described above.
I am probably one of the less experienced members of this community(3 weeks now!) when it comes to color processing, and the accuracy of these color products are clearly debatable. I typically lack confidence in the quality of my work. Neverless, I hope that the results are interesting and enjoyable. I have been flabbergasted by the stuff you guys are making over in the MER area, and it has been a major encouragement to work on the Galileo images.

The first time or two it the images looked a bit monochrome. But as of late, you are getting really good at color.

Triple bands, labled for their appearance at low resolutions as a dark line with a central bright stripe, were seen in the G1 global mosaic to have diffuse edges, suggestive of a possible spray of fine material. Seen in greater detail during E6 at Conamara, they were instead resolved as a mass of closely spaced ridges. Belus Linea, the prominent triple band shrouded in ejecta from Mannann'an, was imaged on E14 at an apparent interruption in its otherwise continuous path.

14ESTRPBND01

context

Thanks for explainations on your technique, Orion... IMHO, your work quality appear excellent. Europa surface still really intriguing and I hope you will continue posting more mosaics.
About last image you posted, in addition to the interesting feature you highlighted, there is a ambiguous circular structure in the upper left... it seems a depressed stuff (recent crater or a collapsed region)... some explaination?

Right-sorry I forgot to include that. That's Niamh, a 5km-diameter impact crater.

Thanks.
Based on inside appearance, must be a crater... but must be very recent compared to the bands, even if no radial features are visible around it. Moreover, the layers dug by it appear very uniform, in spite to surface structures (depth is close to 2Km, apparently).
This disappoint me, especially if we trust to tidal bands generaton model.

I Know I'm going out a limb here but my theory on these bands/faults could be mirror images of whats underneath the ice crust.

I see Europa subsurface a very complex and more intensive earth type fault lines.

Basically upwelling form these faults. The Lava lamp theory looks very promising seeing all these spots that just rip open from underneath.

Sometimes I worry that Europa may actually may be to hot internally to support life.

Sorry for the crude theory of mine.





I would like to see what everyone thinks about it aways!

It is exciting to think of Europa as a world with two surfaces... a seafloor and the visible top of the icy shell. The evidence suggests that the crust is "decoupled" from the interior based on the changing orientations of overprinted surface ridges. I'm curious as to the exact mechanism that produces the wildly braided appearance of complex ridge structures like Belus Linea... I've heard the surface at high resolution described as looking like "a ball of string". I've seen models describing the process by which the bizzare cycloidal cracks form, but I have'nt seen anything modeling the formation of ridge features at fine scales. I'm sure vexgizmo might have an idea...

But how hot is "too hot" going to be? Remember that we have life forms living in excess of 400C at the bottom of our oceans, living off of chemicals toxic to us.

^Excellent point.

A broader view of Belus Linea was obtained at the northern end of the 17ESREGMAP transect, which is contiguous with the two sections shown at the beginning of this thread. On E19, an observation was targeted to fill a gap in this portion of the transect as well. The global mosaic from E14 was used here to produce a color version of the scene.

17/19ESREGMAP Belus Linea greyscale

Color version


In addition to this, medium-resolution color images were taken of this area on E11(300m/pxl, narrow strip) and E19(90m/pxl, very high phase angle, oblique).

11ESCOLORS01-02

19ESCOLOR02

The cracking is currently thought to be a combination of two stresses, diurnal and nonsynchronous. Diurnal stress results from Europa's daily orbit about Jupiter, which includes tidal flexing and libration as Europa orbits. Nonsynchrnous rotation stress results from very slow rotation (period >10,000 years) of the decoupled ice shell above the ocean and mantle at slightly faster than synchronous rate--the shell must change shape to respond to the changing position of surface features relative to the tidal axes. It's difficult to explain individual features yet--people are working on it--but these are the leading stress candidates. Polar wander has also been invoked, and recently obliquity changes too (Hurford et al., in the upcoming LPSC). As nonsynchronous rotation proceeds, stress orientations and regimes change, allowing cross-cutting features to form. And from cracks, somehow the ridges and bands form to create the small-scale features seen, but that's another in-progress story....

Does that explain why the lines make a cookie bite mark? They look like half circles attached at each ends.

I'm still at a loss how those are formed!

These are the "cycloidal" features. They are thought to form as a crack propagates at an average rate that matches the changing stress direction due to the diurnal stressing as Europa orbits. This is much easier to visualize than to put into words, so I point you to Greg Hoppa's web page for some words of explanation, and excellent animations:

http://pirlwww.lpl.arizona.edu/~hoppa/science.html

Click to view attachment
The arrow represents the diurnal stress, which rotates and changes in magnitude as Europa orbits each 3.55 days.

This is the abstract of the Hoppa et al. Science paper which first proposed the idea--this is a strong piece of evidence for a subsurface ocean:

Cycloidal patterns are widely distributed on the surface of Jupiter's moon
Europa. Tensile cracks may have developed such a pattern in response to diurnal
variations in tidal stress in Europa's outer ice shell. When the tensile strength
of the ice is reached, a crack may occur. Propagating cracks would move across
an ever-changing stress field, following a curving path to a place and time where
the tensile stress was insufficient to continue the propagation. A few hours
later, when the stress at the end of the crack again exceeded the strength,
propagation would continue in a new direction. Thus, one arcuate segment of
the cycloidal chain would be produced during each day on Europa. For this model
to work, the tensile strength of Europa's ice crust must be less than 40 kilopascals,
and there must be a thick fluid layer below the ice to allow sufficient
tidal amplitude.

Thank you for all for the information of this thread, these cycloidal patterns must then be another indicator that the ocean actually might be there. Adding another piece to the 'case for an ocean' here.

Great Link vexgizmo Good read.

I presume Bob Pappalardo thinks that the cycloids all formed during one of those geological cycles when Europa was undergoing greater tidal heating and thus had a thin Greenberg-type crust, as opposed to its current era of low tidal heating, thick ice crust and solid-state diapirs? We certainly aren't seeing any cycloids forming right now -- despite the great speed with which each individual one is supposed to have formed.

However, this cycloid formation model doesn't predict any sort of average interval between events, does it? Terrestrial fault ruptures happen quite rapidly, but may be hundreds of years in the making...

Perhaps the average tensile strength of the crust is in fact very close to 40KPa, and the cycloids originate at local weak spots. The question then would be what is making a particular point on the crust mechanically weak over time? I vote for warm subsurface plumes of H2O from Europan "black smokers"...

Yes and no. It's true that Europa may have been generally more active long ago, but a thin crust is not necessary in the cycloid model, just an ocean--the surface stress is nearly identical for a 5 km or 20 km thick ice shell. Cycloidal fractures might form now, but it may be only the rare cycloid that develops into a ridge or band and thus becomes visible. But I do believe that the evidence for a slowing in the rate of feature formation (demonstrated well by Figueredo and Greeley) is consistent with waning activity, and that Europa is probably in a relatively dormant stage. It remains to be seen whether a Greenbergian epoch ever really occurs.


Very true... especially if some nonsynchronous rotation stress is required to initiate cracking (in which case the ice strength can be a few times 40 kPa).

I'll only add that I highly recommend the October 2005 issue of Icarus, Volume 177, Issue 2 (pp. 293-578), which was a special issue entitled "Europa Icy Shell."

For those who do not have access to the journal, I know reprints of some of the papers can be found online (e.g., Nimmo and Giese [2005]).

Thanks for all the excellent links and information. I've posted the abstract for the Icarus paper regarding Castalia Macula in the Argadnel Reigo thread. There's a fascinating suggestion as to why it would make a fine landing site for a future mission.

Rhadamanthys Linea, a feature that that seemed to be comprised of a string of isolated dark spots at low resolution, was targeted for a better view on E14, E15, and E19. It looks as if Rhadamanthys is the "one that got away" as far as the pointing of the camera went, with the single-frame E14 shot missing it entirely and the E19 mosaic catching it only in the corner of each image.

19ESRHADAM01

Context view

E15 mosaic with G1 color

14ESVLOFOT01

Yes, the E19 mosaic missed most of Rhadamanthys, as it was targetted using outdated coordinated information.... *sigh* It's great to see this one in context!
VLOPHOT is a Very LOw phase PHOTometry frame (obtained in several colors), which was pointed not at any specific feature, but to the "shadow point" of the spacecraft (0 degree phase angle) to understand the scattering properties of the icy surface.

My apologies for the mistake...from the pointer plot graphs, it looked awfully close to the intersection. Thanks as always for the insights. The imaging team deserves the greatest respect for making the most of a trying set of circumstances, and in most cases, bringing back the impossible.