Water plumes over Europa |
Water plumes over Europa |
Dec 12 2013, 04:55 PM
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#1
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Member Group: Members Posts: 401 Joined: 5-January 07 From: Manchester England Member No.: 1563 |
This seems like the relevant place to post this (could be wrong): Water plumes from Europa? Apologies if it's already been up. The link to the Science article at the bottom doesn't work for me, does anyone have a working link to the original? Cheers.
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Dec 12 2013, 10:02 PM
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#2
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
I have now taken a quick look at the article. An enhanced emission was detected near 90° west longitude. Here is a quick and dirty orthographic render of Europa's southern hemisphere:
If I understand the article correctly the most likely location for the plume source is near longitude 90°W in the far south. As the render above shows, most of the terrain in the area of interest isn't very well imaged although there is a narrow swath of good images near 90°W. There are some Europa diagrams near the top in this interesting blog entry at the Planetary Society website but the diagrams are rather fuzzy and it's not completely obvious to me what they are showing or where - possibly the location of a likely source region. It will be interesting to see how this affects the JUICE plans. Plumes like this one should be easily detectable by JUICE - the problem is if they are transient. As currently planned, the closest approach occurs approximately over Thrace and Thera Macula (in the image above, the two dark spots near bottom at 180°W). |
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Dec 13 2013, 04:19 PM
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#3
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
I have now taken a quick look at the article. An enhanced emission was detected near 90° west longitude. Here is a quick and dirty orthographic render of Europa's southern hemisphere: If I understand the article correctly the most likely location for the plume source is near longitude 90°W in the far south. As the render above shows, most of the terrain in the area of interest isn't very well imaged although there is a narrow swath of good images near 90°W. There are some Europa diagrams near the top in this interesting blog entry at the Planetary Society website but the diagrams are rather fuzzy and it's not completely obvious to me ... Thanks for making that orthographic image. Here is a higher-resolution version of the graphic that I put in that blog entry. It shows a model for stresses along cracks near the south pole when Europa is at apoapsis. Can you identify which specific images contain these cracks? -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Dec 13 2013, 08:44 PM
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#4
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IMG to PNG GOD Group: Moderator Posts: 2254 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Thanks for making that orthographic image. Here is a higher-resolution version of the graphic that I put in that blog entry. It shows a model for stresses along cracks near the south pole when Europa is at apoapsis. Can you identify which specific images contain these cracks? Not unexpectedly, the imaging coverage is somewhat limited. There is a very big map available from the USGS together with an image footprint chart (europa_simp.pdf): http://astrogeology.usgs.gov/search/detail...obal-Mosaic/cub I can't find an image footprint chart for the south polar region at the USGS website now but here is the relevant part from one I downloaded back in 2001 so there might be changes (not big though). The numbers are the same as in europa_simp.pdf. The longitudes were added by me: The northernmost latitude is probably ~55°S (I can't find an exact number anywhere). Much of the terrain in the red ellipse has been imaged at 1.5-2 km/pixel resolution. The main/only exception is what's labeled as 13 in europa_simp.pdf mentioned above. These are images from orbit 17, observation id 17ESREGMAP01. These images have a resolution of ~200 m/pixel. More interestingly, observation 17ESSTRSLP01 has images of Astypalaea Linea which is within the red ellipse and has high tensile stress. They have a resolution of ~40 m/pixel and these images are not in the USGS map (their resolution really is too high for a 500 m/pixel map). Photojournal images: http://photojournal.jpl.nasa.gov/catalog/PIA02960 http://photojournal.jpl.nasa.gov/catalog/PIA01645 Interestingly, the terrain in the red ellipse is not in view when the plume was visible - at that time the sub-observer longitude was ~90. If the activity is within the red ellipse it means the plume is seen poking above the limb from behind. I don't know if it's of significance or not but Thrace and Thera Macula aren't very far from the red ellipse. If I have understood everything correctly, as currently planned they are a major focus of interest for JUICE near closest approach during its two close Europa flybys. These two maculae have been considered to be among the most likely places on Europa to be currently active (chaos formation in progress) although I don't remember the exact details. |
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Dec 15 2013, 07:25 PM
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#5
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
One of the tricky factors in our limited Europa coverage is the enormous importance of sun angle. The surface is very rough and low sun angle creates shadows along linear features which appear dark. This is easy to confuse with the albedo differences that pertain to composition (dark -> higher non-H2O constituents).
One of the hypotheses for the darker (low albedo, not shadow) linear features is that emission of subsurface liquids which are "dirty" deposit along open fissures, spraying the dark material to the sides. If this is correct, then the active plumes may exist exactly where linear features with low albedo are most prominent. There are so many unknowns in the above, I couldn't begin to estimate how likely this is to be true, but at least if one is beginning to consider possibilities, that seems like the possibility to start with. We're not going to get better maps of Europa until a spacecraft sends them back. Theoretical work on the location of stresses is a nice start, but they depend on unknown and (given only the data we have) unknowable parameters concerning the structure of the icy shell. I don't see any way to pin down the origin of the plumes until observations can be made in situ. That's assuming, in fact, that the plumes and their sources are even persistent over a period of years. Maybe 2023's plumes (if any) will be different than the ones observed so far. |
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