Europa's Northern Plains, Triple bands, cycloidial ridges, ect. |
Europa's Northern Plains, Triple bands, cycloidial ridges, ect. |
Feb 12 2006, 02:21 PM
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#16
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SewingMachine Group: Members Posts: 316 Joined: 27-September 05 From: Seattle Member No.: 510 |
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 -------------------- ...if you don't like my melody, i'll sing it in a major key, i'll sing it very happily. heavens! everybody's all aboard? let's take it back to that minor chord...
Exploitcorporations on Flickr (in progress) : https://www.flickr.com/photos/135024395@N07/ |
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Feb 12 2006, 06:23 PM
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#17
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Junior Member Group: Members Posts: 78 Joined: 29-December 05 Member No.: 623 |
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 cycloidial 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... 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.... |
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Feb 12 2006, 08:29 PM
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#18
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Senior Member Group: Members Posts: 1276 Joined: 25-November 04 Member No.: 114 |
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! |
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Feb 12 2006, 10:16 PM
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#19
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Junior Member Group: Members Posts: 78 Joined: 29-December 05 Member No.: 623 |
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 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. |
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Guest_Myran_* |
Feb 12 2006, 11:21 PM
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#20
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Guests |
QUOTE For this model to work ...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. |
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Feb 13 2006, 12:39 AM
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#21
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Senior Member Group: Members Posts: 1276 Joined: 25-November 04 Member No.: 114 |
Great Link vexgizmo Good read.
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Guest_BruceMoomaw_* |
Feb 13 2006, 03:30 AM
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#22
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Guests |
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.
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Feb 13 2006, 06:07 AM
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#23
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Merciless Robot Group: Admin Posts: 8783 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
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"... -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Feb 14 2006, 01:44 AM
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#24
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Junior Member Group: Members Posts: 78 Joined: 29-December 05 Member No.: 623 |
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. 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. 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... 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). |
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Guest_AlexBlackwell_* |
Feb 14 2006, 02:06 AM
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#25
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Guests |
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]). |
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Feb 14 2006, 03:57 PM
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#26
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SewingMachine Group: Members Posts: 316 Joined: 27-September 05 From: Seattle Member No.: 510 |
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.
-------------------- ...if you don't like my melody, i'll sing it in a major key, i'll sing it very happily. heavens! everybody's all aboard? let's take it back to that minor chord...
Exploitcorporations on Flickr (in progress) : https://www.flickr.com/photos/135024395@N07/ |
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Feb 14 2006, 04:07 PM
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#27
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SewingMachine Group: Members Posts: 316 Joined: 27-September 05 From: Seattle Member No.: 510 |
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 -------------------- ...if you don't like my melody, i'll sing it in a major key, i'll sing it very happily. heavens! everybody's all aboard? let's take it back to that minor chord...
Exploitcorporations on Flickr (in progress) : https://www.flickr.com/photos/135024395@N07/ |
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Feb 16 2006, 07:01 AM
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#28
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Junior Member Group: Members Posts: 78 Joined: 29-December 05 Member No.: 623 |
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.[/url] 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. |
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Feb 16 2006, 09:27 AM
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#29
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SewingMachine Group: Members Posts: 316 Joined: 27-September 05 From: Seattle Member No.: 510 |
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. -------------------- ...if you don't like my melody, i'll sing it in a major key, i'll sing it very happily. heavens! everybody's all aboard? let's take it back to that minor chord...
Exploitcorporations on Flickr (in progress) : https://www.flickr.com/photos/135024395@N07/ |
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