Four years later...

Has it really been four years since I last updated this blog?  It's hard for me to believe, but yes, it has been quite a while.  As I mentioned in that last post, the blog really started to mess with my work/life balance quite a bit when I started doing the "Io Volcano of the Week" feature.  It was a neat idea for generating fresh content for this site, but I ended up spending a ridiculous amount of time on those posts, to the detriment of the rest of my free time.

I think with Discovery proposal season wrapping up and all the warm, over-optimistic feels that generates, I think now is a good time to revive The Gish Bar Times blog, but I really want to go back to focusing on new papers, missions, and data rather than trying to generate a lot of fresh content that took up way to much of my free time and quickly left me worn out.  I think I had this feeling that I always had to come up with more posts when honestly, the focus of this blog is not generating much news right now, and that's okay.

That being said, I do have a long backlog of papers that I haven't discussed here in the last four years, so I should run out of things to talk about here for a while.  My favorite part about doing this blog is that it really forced me to read the current literature and writing articles about them really helped to reinforce what I read.

In the meantime, I wanted to point out this neat site which presents planetary maps for children, including Io, Europa, Mars, Venus, and Titan. The maps were created by a group of graphic artists for the ICA Commission on Planetary Cartography.  The Io map (a portion of which is shown at the top of the post) was created by Dóri Sirály.  I kinda wish the Titan map had more of a medieval map art style (like I keep saying I want to make myself...) but I think these are all well done.

Link: Planetary Maps for Children [childrensmaps.wordpress.com]
Link: Planetary Map Series for Children (LPSC abstract) [http://www.hou.usra.edu]

LPSC 2010: Comparing the Distribution of Io's Paterae

For the last couple of weeks, we have been examining the Io-abstracts submitted for next month's Lunar and Planetary Science Conference.  Today we take a look at a paper submitted by Brandon Barth, Jani Radebaugh, and Adam McKean titled, "Distribution and Comparison of Io's Paterae: Areas, Effective Diameters, and Active Volcanism".  In this paper, the authors discuss measurements of volcanic depressions on Io's surface, known as paterae, and dark paterae floor material.  The authors then studied the size-distribution of paterae across different quadrants of Io's surface.  This research will be presented as a poster at the Satellites and their Planets session on Thursday, March 4.  Last year, this group presented their research on the distribution of paterae (both in general and those with dark material on their floors) at last year's LPSC.  This year, they add the size of the volcanoes found into the mix.

For her PhD dissertation, co-author Jani Radebaugh created a database of paterae back in 2003 and 2004 based on measurements from Galileo and Voyager images, along with parallel MySQL databases of thermal hotspots and mountains.  I still remember the pizza involved, yes, even 7±1 years later... The measurements of the length and area for this database were made assuming that these patera were ellipses, however many paterae as you can see in the image above have complex shapes.  For example, Yaw Patera is shaped like a gasoline nozzle, as seen in the I27 CAMAXT01 mosaic where Yaw is the dark patera in the lower right corner.  Now, one of her students, Brandon Barth, has measured 426 paterae (minus 30 or so in the polar regions still to be measured in time for the poster session) using ArcGIS™.  This allowed Barth and the other co-authors to calculate the size and areas of these oddly-shaped volcanoes more accurately as they are able to mark the boundaries of the patera and ArcGIS does the work in calculating the area of the marked region.

From these measurements, the average effective diameter for paterae on Io is 56.8 kilometers.  Effective diameter is the size of a circle with the same area as the paterae, which aids in comparing the sizes of paterae to one another by normalizing them.  The average effective diameter found is quite a bit larger than Radebaugh et al. 2001, where it was found to be 41 km.  The authors attribute this discrepancy to the measurement techniques mentioned above employed in the different works.  This new method ensures that the entire volcano is captured in the area measurement.

The authors looked at how the size-distribution of all paterae and active paterae (those with at least some dark material on their floors) varies across Io's surface.  They determined that the anti- and sub-Jupiter quadrants of Io have more paterae than the leading and trailing quadrants.  They define these quadrants as the 90 degrees of longitude surrounding the sub-Jupiter (0°W), anti-Jupiter (180°W), leading (90°W), and trailing (270°W) points.  However, they also found that the average effective diameter for the leading and trailing quadrants was larger (63.5 km) than those found on the anti- and sub-Jupiter quadrants (52 km). A similar trend was seen in active paterae, with active paterae being larger than inactive ones on the trailing and leading quadrants and vice versa for the sub- and anti-Jupiter quadrants.  This distribution may have consequences for how Io's releases its heat since paterae are the dominant contributor to Io's total heat flow.

I am curious how much image resolution plays into this.  The resolution of images of Io from the Voyager and Galileo missions is best on the sub- and anti-Jupiter quadrants, respectively.  Better resolution would allow for better identification of paterae margins and would allow smaller paterae to be resolved.  This issue may be most acute on parts of the leading quadrant where the best images have a pixel scale of around 9 kilometers per pixel.  Such low-resolution data may cause an over-estimate of paterae margins as they are confused with nearby bright or dark flows.  I know that Shamshu Patera looks larger than it really is in the global basemap as a result of a bright flow to the south of the volcano.  So more paterae (from smaller paterae being detected) on the sub- and anti-Jupiter quadrants and larger paterae (from mis-identification of margins due to the low resolution of the available data) on the trailing and leading quadrants would be an expected result from resolution effects.  That being said, the trailing and leading quadrants do have some of the largest paterae I can think of like Loki, Dazhbog, Shamshu, and Zal so maybe there is something to this hemispheric difference in average paterae size after all.  Just looking at the poster in front of me, I can only quickly see west Tvashtar and Mentu in that ballpark on the anti-Jupiter side.

This isn't meant as a criticism of their work.  Their methodology is sound; using ArcGIS is an excellent way to measure areas of irregular surface features.  Every day conclusions are made from less than ideal data; science doesn't stop just because the effective resolution of a basemap isn't uniform.  You make do with what you have and just attempt to remain humble when in future years better images are acquired and your conclusions have to be changed.  Look at Titan - a world full of less than ideal data.  When a cryovolcano turns into just another patch of bright material surrounded by dunes, you suck it up and move on.  But you don't let methane windows, low spatial resolution data, or ambiguous terrain stop you from making interpretations and measurements.

Link: Distribution and Comparison of Io's Paterae: Areas, Effective Diameters, and Active Volcanism [www.lpi.usra.edu]

Io Maps from Galileo orbits G7 and I32

As I mentioned yesterday, one of the little side projects I have been working on has been to create color maps of Io for each Galileo orbit we have color data from (though I did create a clear filter map from C3).  This would allow for easier comparisons between Galileo orbits of Io's surface changes (though note that Io has some funky phase angle brightness changes between different regions on the surface that can complicate matters).

This evening, I finished the maps for G7 (April 1997) and I32 (October 2001).  The other maps can be found by browsing my Galileo Images of Io website.  With these two maps, I have expanded the cutoff I use to trim the images in both incidence angle (an angular measure of distance from the sub-solar point) and emission angle (an angular measure of distance from the sub-spacecraft point).  So these new maps show features a little closer to the terminator and limb, respectively, than before.  I think the numbers I am using now for the lunar-lambert function seem to be a better fit than what I used before, making this possible (basically 0.2 above what I would have used before).

I think this is the last pair for a little while.  Cassini is really starting to heat back up again with data coming down in a few hours (sleep for me tonight will be a cat-nap really...) from encounters with Aegaeon (yes, Joe, those six pixels are what I am looking for the most...), Prometheus, and Dione.  Later today we have a Titan flyby where ISS will be prime at closest approach for one of two times during the extended mission.  So yeah... :-)  I will try to get another post out about one of the LPSC abstracts later today if I have some time.

Link: Galileo Images of Io - G7 [pirlwww.lpl.arizona.edu]
Link: Galileo Images of Io - I32 [pirlwww.lpl.arizona.edu]

Io Maps from Galileo orbits E4 and E6

Last year, I started a little project to create color maps of Io for each Galileo orbit there was color data.  The intention was to make it was easier to illustrate surface changes by combining these maps into a single Photoshop file.  Last January and February, I managed to get through G1, G2, C3, C9, G29, and I31.

Over the last two evenings, I've gone ahead and added two more orbits to the list: E4 and E6.  These two orbits from the middle of Galileo's primary mission occurred in December 1996 and February 1997, respectively.  The E6 map is particularly useful as it is one of the few orbits for which a nearly global map was acquired, though one of the observations, E6ISRA____01 had many of its color frames cut off.

In addition to finishing these two maps, I also have two new reprocessed versions of a couple of observations: E4ISGLOCOL02 (shown above) and E6ISRA____01.  While these both are processed to provide a view of Io in color that is not overly saturated, the E4 observation uses a near-infrared filter centered at 756 nm for red and a violet filter for blue, so the color isn't exactly what you would see with your naked eyes, but it is the closest you are going to get with this data set.

I hope these maps are at least interesting to some of you.  Tomorrow evening, I will see about whipping up ones for G7 and I32.

Link: Galileo Images of Io - E4 [pirlwww.lpl.arizona.edu]
Link: Galileo Images of Io - E6 [pirlwww.lpl.arizona.edu]

LPSC 2010: Analysis of the new Io Global Geologic Map

The next abstract we will take a look at is "Volcanism on Io: Results from Global Geologic Mapping" by Dave Williams, Laszlo Keszthelyi, Dave Crown, Paul Geissler, Paul Schenk, Jessica Yff, W.L. Jaeger. The authors completed a global geologic map of Io over the last few years in ArcGIS™ based on a basemap containing Voyager and Galileo created by the USGS.  Their map has gone through peer-review, but has not been published online as far as I know (I'd love to be proved wrong though).  Geomorphologic maps such as this global one can be used to determine the distribution of different terrain types across a planetary surface.  Progress on this project was reported earlier at the last few LPSCs, including 2008 and 2009, as well as other other conferences like EPSC.  This year's paper will be presented as a poster at the "Satellites and their Planets" session on Thursday, March 4.

This year, the authors of the global geologic map will present statistical analyses of the units in the map, which include: plains, lava flows, paterae, mountains, and diffuse deposits.  This involves looking at where certain units and sub-units are most concentrated and how different sub-units are correlated.  As an example, they found that bright flow fields outnumber dark flow fields 3 to 2.  These are considered the youngest flows on Io, composed of sulfur compounds and silicate basalt respectively.  They note a concentration of bright flows at 45-75° N, 60-120° W, covered in the area shown at right.  Williams et al. argue that this region might be indicative of extensive sulfur volcanism here in the past.  An alternative explanation, particular given what happened at Thor (bottom center in the image at right, far right in the Thor link), would be that these flows are older silicate flows that have been coated with sulfur in falling from nearby plumes.  While these flows are old enough to be completely coated and turn a bright shade of yellow, they are not old enough to have been converted to red-brown sulfur (S₄) through radiation damage.  So these flows stand out against the background plains, while at the equator, they might not have been as noticeable.  Thus the process of a lava flow aging and becoming indistinguishable from the background might take longer at the poles than at the equator.

Comparing the distribution of Io thermal hotspots (indicative of volcanic activity) to terrain type, the authors found that 20.3% of hotspots are associated with dark flow fields, 9.3% with undivided flows (older mapped flows, like the ones at lower left in the color image above), 45.3% with dark patera floor material, 1.7% with bright flows, and 18.6% with other patera floor units.  This matches with intuition that recent active volcanism on Io is dominated by silicates.  One difficulty that would be interesting to see how they address are surface changes on Io over the course of the Voyager and Galileo missions, and between them.  For example, hotspots associated with undivided or bright flows may well come from fresh dark flows that formed after the images used in the basemap were taken, as would be the case for Thor.  Activity from Pillan in 1997 would also not be represented in the map since they don't appear in the basemap.

In additional analysis, the authors found that lineated mountains tend to be taller than other mountain that show signs of mass wasting.  This is as expected as mountains are thought to be uplifted crustal blocks that almost immediately begin to waste away.  When looking at diffuse deposits, they found that these materials are dominated by condensed gas deposits from volcanic plumes as opposed to pyroclastics, the latter normally associated with transient outburst-class eruptions, like Pillan or Thor, though some pyroclastic deposits seem to be more permanent around some volcanoes like Pele and Babbar.  Finally, they note that white plains, composed of sulfur dioxide ice fields, are mostly concentrated along the equator on the anti-Jupiter hemisphere in regions such as Colchis Regio, Bosphorus Regio, and Bulicame Regio.  They suggest that this region might be a colder region of Io's surface, possibly due to differences in magma sources, delivery mechanisms, and crustal thickness, but I wonder if runaway thermal segregation, the kind seen on Iapetus, might be a possibility.

In this abstract, Williams et al. once again take a look at the global geologic map the group has created over the last few years, attempting to use the map to determine correlations between different surface units and other Io data, such as mountain height and volcanic hotspots.  Hopefully, sometime in the next year, the map will be officially published, like the Ganymede map was last year.

Paper: Geomorphologic Mapping of Hi'iaka and Shamshu Regions

On Friday, a new paper was published in press in the journal Icarus titled, "Geologic mapping of the Hi’iaka and Shamshu regions of Io".  In press articles are those that have been reviewed and approved for publication, but have not yet been published in the print journal.  This paper, by Melissa Bunte, David Williams, Ronald Greeley, and Windy Jaeger.  This paper discusses the results of a geologic mapping project based on the 25ISTERM__01 mosaic of the Hi'iaka region and the 27ISSHMSHU01 mosaic of Shamshu region [I've also uploaded labeled versions of these two mosaics, Hi'iaka and Shamshu, to help people with this discussion].  These two regions are dominated by a patera with a floor partially covered in dark lava flows surrounded by several large mountains.  This paper is part of a series of geomorphologic mapping projects using medium-resolution Galileo mosaics of Io for their basis.  We previously covered papers discussing maps of Prometheus and Zal.  Other regions mapped by the ASU group include: Chaac-Camaxtli, Culann-Tohil, Zamama-Thor, and Amirani-Skythia-Gish Bar.  In March, I covered this group's LPSC abstract covering the mapping of Hi'iaka and Shamshu, so bare with me if I repeat some things from that post..

For this paper, the authors created two geomorphologic maps of the regions surrounding Hi'iaka and Shamshu Paterae, two volcanoes near Io's equator on the leading hemisphere.  These maps were based primarily on two SSI mosaics from Galileo's I25 and I27 encounters with Io in November 1999 and February 2000, respectively.  Color information and low phase brightness information was taken from the global color mosaic produced by the USGS.  Geomorphologic maps are a type of geologic maps where different surface units are identified and mapped so that relationships between these different units can be identified.

In the case of the Hi'iaka and Shamshu regions, four basic units types were identified: plains material, mountain/plateau materials, patera floor materials, and lava flow materials.  These units were also identified in the mapping of other regions on Io, though diffuse material, recent surface coatings that are derived from volcanic or sapping processing and identified in other mapped regions, was not identified in the Hi'iaka and Shamshu regions.  It should be noted though that diffuse materials are often transient; red diffuse material was observed in a faint partial ring of material surrounding Hi'iaka during Galileo's first orbit of Jupiter, suggesting the presence of a plume at Hi'iaka shortly before June 1996.

These four basic units were further sub-divided into different sub-units based on their albedo, color, surface texture, or structural contacts.  For example, mountain units are divided into lineated (ridged/grooved material, generally found at higher altitudes, bounded with plains by scarps), mottled (hummocky, often with lobed margins), undivided (intermediate in texture and altitude between the mottled and lineated types), and plateau (flat-lying terrain with smooth or hummocky textures) types.  Based on the spatial relationships between these units, the authors theorize that these types represent different stages of degradation on Io's mountains.  Lineated mountain units tend to be higher standing and have sharper unit contacts with the surrounding plains, suggesting that terrains of this unit have undergone the least amount of degradation.  The ridges and grooves, such as those seen above at north Hi'iaka Montes, are the result of down slope slumping of a mobile surface layer atop the mountain (see Jeff Moore's 2001 paper on slope degradation on Io).  Remember that mountains are thought to be tilted crustal blocks, the ridged and grooved top surface of the mountain is the result of the upper few kilometers of the mountains, which is a mix of basalt and sulfurous materials that was once part of the upper few kilometers of Io's flat plains.  Once that upper layer sloughs off, the unit transitions to the undivided or mottled types (though the mottled types are likely a mix of old mountain and the mass wasted materials surrounding the mountain).

A similar age progression in sub-units was also noted in patera floor and lava flow materials based on color and albedo (for dark flow/patera floor materials, darker equals younger).  The paper only mentions briefly the debate whether some bright or yellowish lava flows are primary or secondary sulfur flows, or silicate flows with chemical altered surfaces.  The authors (and I agree) that these flows are likely old silicate flows.  This supported less in this region but at Thor, where an outburst eruption generated lava flows that overlapped those of an older, yellowish flow.  Exceptions to this could include a bright white flow to the south of Shamshu Patera and the orange floors of "Mekala Patera" and western Hi'iaka Patera, which could be due to mobilized sulfur dioxide and sulfur, respectively.

As I mentioned in my post from March on the researchers' LPSC abstract on this subject, the authors examined the hypothesis that the three mountains that surround Hi'iaka Patera had at one point been part of a single structure that had split apart as a result of strike-slip and extensional faulting.  This fault would have also resulted in the creation of pull-apart basins that would become Hi'iaka Patera and orange-color patera to the lower left of north Hi'iaka Montes (named Mekala Patera in the paper).  The authors note that the freshest lava flows on the floor of Hi'iaka appear to emanate from the eastern and southern margins of the patera, a pattern consistent with this break-up scenario.  This model of regional-scale plate tectonics was also applied to the mountains in the Shamshu region (with Shamshu Patera being presented as a pull-apart basin) with less convincing results, but it does suggest a new line of investigation to see just how prevalent this style of plate tectonics is on Io with mountains forming, breaking apart, and shifting around across Io's surface.  How many other close groupings of mountains were the result of a single mountain being broken apart by strike-slip and extensional faulting?  I should note that several Ionain mountains have been observed with canyons running down the centers as a result of extensional faulting, like Ionian Mons (upper left), Mongibello Mons, and Danube Planum.

This paper summarizes the results of geomorphologic mapping of the Hi'iaka and Shamshu regions on Io based on regional-scale imaging by Galileo, finding units consistent with those found in other regional mosaics of the satellite.  The geologic history of these regions based on their mapping supports earlier research into this area by authors like Turtle et al. 2001 and Jaeger et al. 2001 that Hi'iaka Patera formed as the result of Hi'iaka Montes breaking apart by strike-slip and extensional faulting.  Magma then ascending to the surface using these same faults that bounded the pull-apart basin.  At this point, the volcanic activity at both Hi'iaka and Shamshu appear to be dominated by compound lava flows, unlike the lava lakes seen at Pele and Loki.  The mountains were then further degraded by gravitational mass wasting, SO₂ sapping from ice layers within the mountain, and thermal erosion from nearby volcanoes.  Thermal erosion by flowing lava is thought to be responsible for Tawhaki Vallis, a channel observed to the right side of the image at top, as proposed by Schenk and Williams 2004.  Each of mountains in the region exhibit signs of degradation, from the ridges and grooves atop north Hi'iaka Montes and north Shamshu Montes, indicative of a slumping mobile surface layer, to hummocky-textured and lobe-edged landslide deposits, indicative of gravitationally- or sapping-induced mass wasting.

I think that leaves one more region to map, Tvashtar.

Link: Geologic mapping of the Hi’iaka and Shamshu regions of Io [dx.doi.org]

A Few New Io/Jupiter System Papers

Sorry for the hiatus there is posts over the last couple of months.  I've just been a bit busy with Cassini plus I wanted to take a bit of a break after posting so much in September and October.  I wanted to post a quick note letting you all know about three new Io/Jupiter System related papers currently in press in the journal Icarus.

The first is titled, "Geologic mapping of the Hi'iaka and Shamshu regions of Io" by Melissa Bunte, David Williams, Ronald Greeley, and Windy Jaeger.  This paper is the latest in a series that covers the geologic histories of some of the regions observed at high- and medium-resolution by Galileo during its flybys in the late 1990s and early 2000s.  Back in March, I covered the authors' LPSC abstract on this research so you can read up on that while I slowly get through this paper and post a summary over the weekend (hopefully, there is a major Titan flyby today whose data comes back Sunday morning).

The other Io paper is titled, "Multi-wavelength simulations of atmospheric radiation from Io with a 3-D spherical-shell backward Monte Carlo radiative transfer model" by Sergey Gratiy et al.  Yeah, that's going to take me a bit longer to get through.  Hopefully I can post something next week.

The final paper that caught my eye in Icarus is titled, "Global geological mapping of Ganymede" by G. Wesley Patterson et al.  This paper discusses the completed Ganymede global geologic map and presents research on the observed geologic units on that satellite.  Again, I've only flipped through the article, and maybe later this month I can write up something about it.

LPSC 2009: Classifying Io's Paterae

Continuing my series of posts covering the Io-related abstracts submitted for this year's Lunar and Planetary Science Conference, we come to "Classification of Io's Paterae: Active vs. Inactive" by Brandon Barth, Jani Radebaugh, and Eric Christiansen. This abstract takes a look at the distribution of paterae across Io by breaking the paterae down into those with dark floors and those without.

Paterae are volcanic depressions on Io's surface. They display a variety of morphology though they often have one or more linear margins, suggesting tectonic control, and have various volcanic landforms on their floors. Some, like Pele, appear to have an active lava lake covering part of their floors. The latest theory for their formation, put forward by Keszthelyi et al. (2004), is that they start out as intrusive volcanic sills, where magma stall between two layers of rock in the upper lithosphere. Magma in the sills then burn off any volatiles in the crust above them and slowly melt the remaining rock until a shallow depression is filled. The linear margins represent fault planes magma use to ascend from deeper magma chambers. Radebaugh et al. (2001) counted and measured more than 400 paterae across Io's surface from Voyager and Galileo imagery and found that they average 41 km in diameter, larger than similar volcanic depressions on Earth, Venus, and Mars. Radebaugh et al. in 2001 also found that paterae tend to be concentrated near the sub- and anti-jovian longitude but are displaced by 30° to the east suggesting the potential for non-synchronous rotation. Radebaugh and her colleauges later created a relational database with various parameters (such as non-circularity and the presence of dark flows) mapped and measured for 428 paterae. I remember pizza being involved...

For this abstract, Barth and his two advisers have gone back and mapped out these paterae, focusing on the color of each volcano, whether they are coated completely in dark material, only have some dark material covering their floors, or have no dark material at all. This goes a bit further than the earlier database developed in 2003 did when only the presence of dark materials were noted, not the percentage of coverage [at least not the version of the database I still have]. The authors examined their map to see how the distribution of paterae with dark floor materials compared to those without and to the general paterae distribution. Dark paterae material represent the surfaces of lava flows or lava lakes that are either active or haven't cooled enough to allow frost to condense on them, which would increase their albedo. The authors believe that mapping paterae with at least some dark floor materials acts as a good proxy for searching for volcanic hotspots, particularly in areas with poor thermal data from Galileo, such as across much of the leading and pro-jovian hemispheres. This is supported by high resolution thermal imaging of the Chaac-Camaxtli region, as noted in Williams et al. (2002), where all the areas where dark material was observed by SSI was associated with a hotspot.

The authors noted some issues while mapping. For example, it became difficult to distinguish dark green material and black material. Green paterae floor material can result from the condensation of sulfur on still warm silicate flows or lakes. Another issue that arose was the low resolution of much of parts of the leading hemisphere, which made it difficult to resolve paterae boundaries. It also appears to have led some mountains being mapped as paterae, like Ethiopia Planum and Pan Mensa.

Their initial results suggest that paterae with dark floor materials have a similar distribution to the general population of volcanoes on Io. Like all paterae, there are peaks in longitudinal distribution centered near 150° and 330° supporting their initial hypothesis. They also find a slight difference in the number of active paterae between the sub- and anti-jovian hemispheres of Io, with 10% more in the anti-jovian hemisphere. There might be an observational bias due to the lower resolution between 30° and 70° on the sub-jovian hemisphere. Finally, they found a correlation between the size of the patera and the percentage of dark floor material. Large paterae tend to have a smaller percentage of dark material than smaller ones, suggesting that the size of paterae may not be related to the size of magma chamber. Therefore both large and small paterae would have similar amounts of magma available for an eruption, so large paterae would be more difficult to coat with fresh lava.

The authors present this as a work in progress. They hope to further look at the connection between patera size and amount of dark material cover. Perhaps this could be linked with the geologic map Dave Williams and his colleauges have created as this would seem like a perfect example of the kind of statistical analysis that could be performed on the map. This would certainly justify all the misery the main author has had with ArcGIS he has mentioned on his blog. Research into paterae distribution, particularly ones with fresh deposits, can be useful in better understand heat flow in Io's interior. Radebaugh et al. (2001) and other studies found that paterae and hotspot distribution peaks near the sub- and anti-jovian points is consistent with tidal heating being centered in the asthenosphere. Though I wonder why recently active paterae show the same displacement from those points, since I would think there would be less lag for active lava flows as opposed to more stable geologic structures like volcanic pits.

Link: Classification of Io's Paterae: Active vs. Inactive [www.lpi.usra.edu]

LPSC 2009: Insights from Global Geologic Mapping of Io

The other mapping poster that will be presented at LPSC this year is by Dave William et al. and is titled, "Volcanism on Io: Insights from Global Geologic Mapping". This poster will present the status of the global geologic map project as well as present examples of results derived from the map. The authors' LPSC 2008 update was discussed on this blog last year.

The geologic mapping group finished the global map last year in ArcGIS. They are now working on a database to incorporate information about surface changes observed by Galileo, Voyager, and New Horizons.

This abstract two examples of statistical analyses that have been performed on the geologic map. The first compares the height and area of various mountain units. The authors find that lineated mountains tend to be taller than mottled mountains. This supports the hypothesis that mottled mountains are more degraded, and thus older, version of the younger lineated mountain unit. However, based on the plot of mountain height-vs-area, they may be dealing with statistics of small numbers as only 4 mottled moutains are plotted. The layered plains unit, thought to be an even more degraded mountain unit, has a similar area distribution as the other mountains units, but tend to be restricted to under six kilometers in height, further supporting formation from degradation.

The rest of the abstract is spent looking at the temporal correlation of mapped units. Williams et al. propose that mountain units are the oldest geologic unit, forming over a period from several millenia ago to perhaps several million years ago. This is based on the observed pattern of degradation at the various mountains mapped on Io (lineated mountains -> undivided mountains -> mottled mountains -> layered plains) and the superposition of other units on mountains such as diffuse volcanic deposits and paterae (seen at some mountains to be "eating" into them, such as at Tohil Mons and Gish Bar Mons). Volcanic units have formed much more recently, with diffuse deposits and dark and bright flows (both on the plains and in paterae) forming during the period of spacecraft observation. Plains units fill in the gap between volcanic units and mountain units, the result of the buildup volcanic deposits and mountain mass wasting that have since become homogenized and can not be split into different units (like undivided flows).

Again, another interesting paper, but I am curious as to when or if the geologic map will be available online as a downloadable product like some of the older Galilean satellites maps or the Venus geologic maps.

Link: Volcanism on Io: Insights from Global Geologic Mapping [www.lpi.usra.edu]

LPSC 2009: Geologic Mapping of the Hi'iaka and Shamshu Regions of Io

The next LPSC abstract I want to discuss here is "Geologic Mapping of the Hi'iaka and Shamshu Regions of Io" by Melissa Bunte, Dave Williams, Ron Greeley, and Windy Jaeger. The poster will cover geomorphologic maps of the regions around Hi'iaka Patera and Shamshu Patera based on medium-resolution imagery acquired during Galileo's I25 and I27 encounters and the lower resolution color mosaic taken during orbit C21. Both volcanoes are in the equatorial region on the leading and sub-jovian hemispheres. This abstract presents an update of the ASU groups regional geologic mapping of Io that has previously covered: Chaac-Camaxtli, Culann-Tohil, Zamama-Thor, Amirani-Skythia-Gish Bar, and Zal.

Both regions mapped by the ASU group have complex examples of the interaction between tectonics and volcanism. At Hi'iaka, there are three mountains, two L-shaped mountains named North Hi'iaka Montes (the entirety of which can be seen at right), South Hi'iaka Montes (a degraded plateau to the southeast of the north segment), and West Hi'iaka Montes (a footprint-shaped isolated peak to the southwest of South Hi'iaka). The authors state that their mapping of this part of Io supports the theory that North and South Hi'iaka Montes were once a single mountain that rifted along its long axis (a process seen at several mountains on Io, like North Boosaule Montes and Danube Planum) then underwent right-lateral strike-slip faulting that left mountains in their present locations. The authors then propose that this tectonic motion opened up a depression that would become Hi'iaka Patera. Another interesting tectonic-volcanic interaction in these regions is the extensional fault that NE-SW through Shamshu Mons that also has a small patera along its length (a volcano the authors call Perun Patera, though that name would never be approved since there already is a volcano on Io named after Perun, Pyerun Patera). This, along with the youngest flows within patera following visible fault lines, supports the idea that magma use pre-existing fault lines as conduits for ascent.

Another theory the authors tested with these maps is whether differences in mountain morphology are related to age and state of degradation. The mountain units types the authors mapped include lineated, mottled, undivided, and plateau mountain material. According to the abstract, "Mapping results support the theory that mountain units can be uplifted and tectonically modified [like the rifting seen at Hi'iaka and Shamshu Montes], then sloped, scalloped, and leveled by SO₂ sapping". The authors suggest that the mountains start out lineated with moderate mass wasting but with many of the original imbricate faults and sub-surface layering still visible. These then degrade into undivided mountain material, a combination of mottled and lineated materials, and then mottled material, which contains hummocky material and a patchwork of bright and darkish material. SO₂ sapping at Hi'iaka Montes is evidenced by the bright white plains material that follow the slopes of both North and South Hi'iaka, as well as parts of Shamshu Mons.

Overall an interesting paper about a very intriguing region on Io. The only complaint I have is that there really is only one more region to map based on available Galileo imaging -- the area around Tvashtar Paterae.

Link: Geologic Mapping of the Hi'iaka and Shamshu Regions of Io [www.lpi.usra.edu]

More Galileo Maps

Continuing the project I started last month, I have posted on my Io images page several more Io maps from several of Galileo's orbits, including from G1, C3, G29, and I31. These maps help illustrate some of the surface changes documented by Galileo during its six years of observations while in orbit around Jupiter. For example, comparing the maps from G29 and I31 (shown at right), you can see several new plume deposits, including a bright ring around Thor (which was undergoing a major eruption during August 2001), a red ring around Dazhbog, and a faint deposit around Surt (probably a faded red ring from the major eruption that took place in February 2001, still the most powerful volcanic eruption ever witnessed).

I am still considering producing some sort of product that combines these and other maps of Io as layers in a photoshop file for example. Photoshop isn't quite ArcGIS, but it'll do.

Link: Galileo images of Io [pirlwww.lpl.arizona.edu]

Geologic Mapping of the Zal region of Io

There is a new article in press in the journal Icarus titled, "Geologic Mapping of the Zal region of Io," by Melissa Bunte, David Williams, and Ron Greeley. A summary of their results was presented in March at the Lunar and Planetary Sciences Conference and was reported on here. Now the full paper is available on the Icarus website (subscription required to view paper). This paper is based on imagery acquired during the I25 and I27 Galileo encounters with Io.

Like many of the regions mapped by the ASU previously, such as near Camaxtli Patera, Tohil Mons, Amirani, and Thor, the authors mapped 5 basic units in the region: mountains/plateaus, smooth/layered plains, patera floor material, flow material, and diffuse materials. The flow features in this area appear to be generated from a small patera lying near the western margin of South Zal Montes (they propose the name "Rustam Patera" for this volcano) or from a fissure that runs north from "Rustam" along the western margin of South Zal Montes and the eastern margin of North Zal Montes. The flows include bright flows (possibly of sulfurous composition) radiating out from "Rustam" and dark flows which flow east across part of Zal Patera from the northern part of the fissure. Additional flow features are also seen within Zal Patera, but these appear to be older in age based on their brighter appearance.

One interesting hypothesis made in this paper is that the various components of Zal Montes, which surround Zal Patera to the west, east, and south, were originally part of a single structure. This feature then broke-up due to strike-slip then extensional faulting, opening up Zal Patera. Similar plate tectonics-in-miniature is theorized for formation of Hi'iaka Patera. The paper goes on to describe the degradational processes that have occurred at the mountains in the region.

One feature I wished the paper expounded on further is a small volcano west of North Zal Montes, which they suggest the name "At'am Patera" for. What makes the volcano interesting is that it appears to be one of a very rare breed of explosive Ionian volcano. "At'am" erupted between late-June and mid-September 1997, producing a white, Sulfur dioxide-rich plume deposit and a dark-green pyroclastic deposit with a digitate margin. Some of both materials was deposited on North Zal Montes. The digitate appearance is due to the interaction between the pyroclastic flow and the arcuate margin of the western part of North Zal Montes. This morphology may provide clues on how these pyroclastic deposits are formed on Io. Oddly, for an Ionian eruption, no lava flows or thermal emission were observed at this volcano. Also, the central vent is among the smallest paterae found on Io. It is possible that the 1997 eruption could have been the result of an intrusive event, where magma ascends from a deeper chamber, but fails to reach the surface. However, volatiles and other materials, being more buoyant, do make it to the surface.

The paper does touch a bit on the plume seen at Zal last year by New Horizons. This plume is centered on Zal Patera (unlike the plume deposit seen by Galileo starting in Sept. 1997 which surrounds "At'am Patera"). Zal Patera is also the site of fresh surface changes, which include a new dark plume deposit and fresh dark lava flows.

Link: Geologic Mapping of the Zal region of Io [dx.doi.org] (subscription required to view paper)

LPSC 2008: Heat Flow from Dark Volcanic Fields

I've covered all the Io-related abstracts in tomorrow night's (wait, now tonight's) poster session covering the Galilean Satellites. Yeah, Io got lumped in with *shiver* Europa (in my mind, there are United Nations peace keepers between the Io and Europa poster boards), Ganymede (everyone's second favorite schizophrenic moon), and Callisto (thanks to the discovery of rings around Rhea, Callisto now possesses the sole title of most boring moon ever). So, if you are at LPSC, be sure to visit the poor Ionians as they will most likely shoved along the back wall like they were last year. Please, show them some love.

Anyways, I am rambling on here. There is an additional Io-related abstract submitted to the LPSC conference, a print-only abstracted by Glenn Veeder, Dennis Matson, Ashley Davies, and Torrence Johnson titled, "Io: Heat Flow from Dark Volcanic Fields." The authors examined the distribution of dark flow fields on Io and examine their contribution to Io's high heat flow (the total amount of heat released in a given time period from the interior). As a print-only abstract, the results presented in this abstract will not be presented at a talk or a poster at LPSC.

The authors focused on dark flow fields, areas where lava has flowed across Io's flat(ish) plains, rather than those flows within the topographic confines of a patera. It is thought that these flows are compound pahoehoe silicate lava flows, built up by small outbreaks on top of older flows punctuated by period of high eruption rates that rapidly grow the lava (akin to flood basalts on Earth). They determined that dark flow fields are not distributed evenly across all longitudes with a peak near the center of the anti-Jovian hemisphere (in the abstract, the anti-Loki hemisphere). Flows seen near this peak include Prometheus, Zamama, Thor, Culann, Volund, and Mycenae Regio. This correlates well with a peak in the distribution of volcanic centers and paterae. The authors note that a correlation is not seen at the other peak in volcanic centers and paterae near 325° West, which includes Loki.

The authors then examined the contribution these lava flows make to Io's total heat flow. In the abstract, they focused on two prominent flow fields: Lei-Kung Fluctus (shown above, big flow field on Io's northern trailing hemisphere) and Amirani. Using NIMS and PPR data from Galileo, the authors calculated that that the two lava flows contribute 4.5x10¹¹ W and 1.5x10¹² W to Io's total heat flow, which is on the order of 10¹⁴ W. In total, the 24 flow fields the authors examined contribute approximately 10% to Io's total heat flow, equivalent to Loki Patera. It should be noted that the authors mapped about 3x10⁵ km² worth of dark flows. This is about 25% of the total amount of dark lava flows covering Io's surface according to the mapping done by Williams et al., so that 10% figure maybe an underestimate. I can't tell, but it also seems like they assumed an effective temperature (basically an average temperature for the entire flow field) to come up with their heat flow numbers for at least some of the fields they mapped.

An interesting abstract. I will be interested in seeing how their dark flow mapping compares to what Williams et al. has done (this also sounds like the kind of project that global geologic mapping is suited for), particularly since Williams et al. mapped a factor of 4 more dark flows material than Veeder et al. did.

Link: Io: Heat Flow from Dark Volcanic Fields [www.lpi.usra.edu]

LPSC 2008: Global Geologic Mapping of Io

The final Io-related poster that will be presented during Tuesday's poster session at the Lunar and Planetary Sciences Conference is titled "Global Geologic Mapping of Io: Preliminary Results" by Williams et al.

This is an update on the author's three-year global mapping project. They are nearly finished with their work and will present a preliminary version of their global geologic map at LPSC. They hope to have a completed version submitted to the USGS by June.

Global geologic maps help scientists assess the relationships between different types of terrains as well as calculate what percentage of the surface is covered by a particular unit. For example, one project the author's plan on using the map for is to determine whether NIMS hotspots are correlated with dark lava flows, while PPR hotspots are correlated with bright lava flows. The Near-Infrared Mapping Spectrometer (NIMS) was sensitive to shorter, infrared wavelengths (1-5 microns) and thus sensed thermal emission from hotspots with temperatures greater than 200 K, often warmer than that when NIMS observed the day-side of Io. The Photopolarimeter-Radiometer (PPR) was sensitive to thermal infrared wavelengths and thus looked at cooler hotspots down to those just above the background temperature. At several locations, these hotspots were not correlated, suggesting that some PPR hotspots were related to sulfur volcanism, while NIMS hotspots were related to silicate volcanism. The authors plan to investigate that possibility.

Based on their geologic map, the authors determined that the most common surface type on Io is the plains unit, covering 66% of the surface. The next most common is the lava flow unit, covering nearly 28% of the surface.

By the way, if you want to read all of my posts covering the Io abstracts for this year's LPSC conference, you can check out the special page just for them. Still got one more to go.

Link: Global Geologic Mapping of Io: Preliminary Results [www.lpi.usra.edu]

LPSC 2008: Geologic Mapping of the Zal Region of Io

The Lunar and Planetary Sciences Conference is coming up in a couple weeks. I unfortunately will not be attending but the abstracts for the conference, which are almost mini-papers in length, have been online for a few weeks now. Nearly all the Io-related abstracts are for posters to be presented on the evening of Tuesday, March 11. In this post, and in blogs to be posted over the next week or so, I will cover one of the abstracts for this conference.

The first abstract I'm going to discuss is "Geologic Mapping of the Zal Region of Io" by Melissa Bunte, David Williams, and Ron Greeley. This abstract covers work done as a part of series of geologic mapping work performed by the Planetary Geology group at Arizona State University on the mosaics Galileo acquired of Io during its seven encounters. This time they cover the area around Zal Patera. This volcano on Io's northern Leading hemisphere is bounded to the west and south by the two-part Zal Montes.

Like most places the group has mapped, they found 5 basic terrain types: plains, mountains, patera floor materials, flow materials, and diffuse materials. Their mapping allowed the authors to determine the age relationships between the different flow units within Zal Patera based on the brightness of the flows. Basically, as a flow ages, it cools (obviously) and as it cools, more volatiles can condense on it. Color-wise, the progression at this latitude is (generally now) from black, to green (when you got your sulfur mixing with your iron), to yellow (thanks to S₈), and then to red-brown when radiation starts to work on the sulfur and break it down (anyone know how long that roughly takes, by the way?). The group also mapped some very extensive, old flows that they attribute to Rustam Patera, the proposed name for an active volcano on the western margin of South Zal Montes.

Following the work they have done previously in the Amirani and Camaxtli regions on Io, they will like publish this work sometime in the next year or so. Certainly will be a paper to look for. I would be interested in how they handle the connection between Rustam Patera and the lava channel that runs north from it up through to what they identify as a fissure along the western margin of Zal Patera. Another interesting feature in this region (or actually just off the western edge of their mapped segment) is a small, explosive eruption from the summer of 1997 that produced a small dark pyroclastic deposit that partly overlaps onto the western margin of the North Zal Montes plateau, which is identified as a flow (?) in the map included in the abstract, and a bright ring around that pyroclastic deposit. Strangely enough, no obvious effusive materials from that eruption.

The ASU group also has another poster at the conference where they present the work they have done so far on producing a global geologic map. I will discuss that abstract in a later post.

Link: Geologic Mapping of the Zal Region of Io [www.lpi.usra.edu][pdf file]