Enjoy Mittens? So does Europa.

Here is another brief research update, based mostly on parts of a paper I wrote. Nothing special but some info on the Mitten.

Galileo launched exactly 1 year before I was born on October 18, 1990. an unmanned spacecraft (Figure 1) that studied the planet Jupiter and its moons.

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Figure 1: Galileo spacecraft artist picturing.

It gathered the best data currently available on the moon Europa. NASA’s Galileo Project gathered images using the Solid State Imaging (SSI) camera on the Galileo spacecraft. The Planetary Data System (PDS) stores the data which is open to the public. It’s managed by the Jet Propulsion Laboratory in conjunction with the U.S. Geological Survey.

We used it look at two pictures, to make one full image of Murias Chaos, informally known as the Mitten (Figure 2).

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Figure 2: The Mitten on Europa (i.e. Murias Chaos)

The topography is useful in identifying the chaotic heights relative to its surrounding. We can use the DEM model to create topographical maps of the chaotic terrain (Kirk et al., 2003). However, these types of maps have already been completed for most chaotic terrain. Figueredo et al. (2002) uses the DEM model to create a 3D mosaic of Murias Chaos (Figure 4) that may be caused by an underwater lens (Schmidt et al., 2011). We can infer, from the surrounding, that original surface wasn’t elevated and might have undergone melting that then refroze to elevate the region. Using this knowledge, we can consider whether the surrounding terrain features might have influenced the formation (e.g. creating an outer boundary or wall for a stronger feature).

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Figure 4: Considering the formation and uplift of Murias Chaos. Schmidt et al. (2011) show the effect of a melt lens within the ice crust (left). Figueredo et al. (2002) use the DEM model to create a 3D mosaic of Murias Chaos (right).

The left side of the Mitten is traced by a deep fracture. This was not an original feature; the uplifted chaos material has pushed down causing the fracture (Figueredo et al. 2002). Further evidence of uplift is the mass wasting seen along the southern border of the chaos terrain. It lies within an area with higher stress. We have not considered overlaying ridges and troughs that span multiple geologic units in our characterization in Figure 3. This will be done in future work, but we have not identified whether or not these influence the chaos formation.

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Figure 3: Murias Chaos (the Mitten) shown on the left, a characterization of the original terrain before the chaos formation using Figueredo et al. (2002) and Figueredo & Greeley (2004) mapping criteria (middle and right). Ridged band material is shown in red, degraded plains material is shown in blue, complex ridge material is shown in yellow, and lineated band material is shown in green. All other terrain is left blank (white) to represent ridged plain material, the predominant surface feature.  The white arrows indicate the angle that the ridged band material is oriented.

Once a chaos terrain is chosen, we begin to characterize the surface prior to the chaotic formation using the features within the chaotic terrain and around it. We begin by identifying the major geologic units identified in our original post first. We can proceed to map outlying ridges, troughs, or fractures. Using the Galileo images and Figueredo et al. (2002) mapping of Murias Chaos contains we have identified five major geologic units: 1) Ridged band material, 2) Degraded plain material, 3) Complex ridge material, 4) Lineated band material, 5) Ridged plain material. We considered three different possible configurations of the original terrain, where the major obstacle is the obscure degraded plans material.

Figueredo et al. (2002) identifies regions north and a small region south of the Mitten. That may be indicative of a large degraded plain region or that degraded plains are commonly localized. However, there is no significant evidence of other degraded planes in this region. This type of smooth, calm region seems unlikely and uncommon. Figueredo et al. (2002) classification of the degraded planes south of the Mitten is also wedged next to mass wasting terrain (from the elevated chaos material) indicating it may not be degraded plains after all. For these reasons, we present a conservative view for the amount degraded terrain.

The ridged band material is the largest geologic unit, aside from the ridged plain material. At the top of the band, two different bands can be seen to come together. On the left, the bands are at an angle of ~20 degrees from the N-S axis. On the right, the bands are ~45 degrees and the ridged plains exhibit the same orientation. This indicates that this location was experiencing two different orientations of stresses all of which meet at the top left of the chaos region. This may have resulted in this region being weaker than the surrounding terrain. It may have been prone to the formation of a subsurface lens due to a higher concentration of energy such that it would lead to the chaos region forming and uplifting (Schmidt et al., 2011).

References

Carr, M. H., Belton, M. J., Chapman, C. R., Davies, M. E., Geissler, P., Greenberg, R., … Veverka, J. (1998). Evidence for a subsurface ocean on Europa. Nature, 391, 363–365. http://doi.org/10.1038/34857

Collins, G., & Nimmo, F. (2009). Chaotic terrain on Europa. Europa, The University of Arizona Space …, 259–281. Retrieved from http://books.google.com/books?hl=en&lr=&id=Jpcz2UoXejgC&oi=fnd&pg=PA259&dq=Chaotic+Terrain+on+Europa&ots=vWUdSwHa7x&sig=lhhxXOlYxxJKVnYIR4yQF-Ekgr8

Figueredo, P.H. Chaung, F.C., Rathbun, J., Kirk, R.L., Greeley, R. (2002). Geology and origin
of Europa’s “Mitten” Feature (Murias Chaos). Journal of Geophysical Research, 107, E5; 2-1 – 2-15. doi:10.1029/2001JE001591

Figueredo, P. H., & Greeley, R. (2004). Resurfacing history of Europa from pole-to-pole geological mapping. Icarus, 167(2), 287–312. http://doi.org/10.1016/j.icarus.2003.09.016

Greeley, R., Figueredo, P. H., Williams, D. a., Chuang, F. C., Klemaszewski, J. E., Kadel, S. D., … Tanaka, K. L. (2000). Geologic mapping of Europa. Journal of Geophysical Research, 105(E9), 22559. http://doi.org/10.1029/1999JE001173

Greenberg, R., Hoppa, G.V., Tufts, B.R., Geissler, P., Riley, J., & Kadel, S. (1999). Chaos on
Europa. Icarus, 141, 263-286. doi:10.1006/icar.1999.6187

Hedgepeth, J., Walker, C. Schmidt, B., Spatiotemporal Intercomparison of Calving Processes
and Crevasse Patterns in Helheim Glacier, Annals of Glaciology, submitted.

Kereszturi, A., & Keszthelyi, Z. (2013). Astrobiological implications of chaos terrains on Europa to help targeting future missions. Planetary and Space Science, 77, 74–90. http://doi.org/10.1016/j.pss.2012.08.028

Kivelson, M. G., Khurana, K. K., Russell, C. T., Volwerk, M., Walker, R. J., & Zimmer, C. (2000). Galileo magnetometer measurements: a stronger case for a subsurface ocean at Europa. Science, 289(5483), 1340–1343. http://doi.org/10.1126/science.289.5483.1340

Kirk, R.L., Barret, J.M., & Soderblom, L.A. (2003). Photoclinometry Made Simple. Advancces
in Planetary Mapping 2003. Retrieved from: http://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/3a534e82-80a3-49dd-80ef-45f5b82391b1/Kirk_isprs_mar03.pdf

Schmidt, B. E., Blankenship, D. D., Patterson, G. W., & Schenk, P. M. (2011). Active formation of “chaos terrain” over shallow subsurface water on Europa. Nature, 479(7374), 502–5. http://doi.org/10.1038/nature10608

Squyres, S. W., Reynolds, R. T., Cassen, P. M., & Peale, S. J. (1983). Liquid water and active resurfacing on Europa. Nature, 301, 225–226. http://dx.doi.org/10.1038/301225a0

Thomas, P.C., Tajeddine, R., Tiscareno, M.S., Burns, J.A., Joseph, J., Loredo, T.J., Helfenstein,
P., Porco, C. (2016). Enceladus’s measured physical libration requires a global subsurface ocean, Icarus, 264, 37-47, http://dx.doi.org/10.1016/j.icarus.2015.08.037

 

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