Friday, February 29, 2008
Okay, okay, I made this last year in Photoshop to be a background for my laptop. It was created by combining an image taken by Andreas Tille in the Eldgjá Fissure in Southwestern Iceland (original image) and a simulated view from the surface of Io (from Gish Bar Patera) of the eastern horizons. I used Photoshop CS to adjust the colors to match those of Io, to blur out the more obvious blades of grass, and to remove some of the distant mountains (due to the obvious atmospheric scattering).
Hope you like.
Link: Jupiter from Gish Bar [pirlwww.lpl.arizona.edu]
Thursday, February 28, 2008
The G2 image, shown at left, was the first observation to cover the anti-Jovian hemisphere during the Galileo mission. the 3-color image was acquired on September 7, 1996. Comparisons between this frame and Voyager images revealed changes at Prometheus (including a new lava flow and a 75-km change in the position of the plume vent), Culann, and Zamama (a volcanic center not visible in Voyager images), as well as at other volcanic centers. During the G2 encounter period, numerous other violet filter images were returned, designed to study Io's volcanic plumes. I have not done anything with these images due to their high compression ratios. This image was released by the Galileo Project as PIA00494.
For E4, I redid the E4ISGLOCOL02 observation. There are a couple of others on that page that I have done new work on. E4ISGLOCOL02 covers much of the same terrain as the G2 iamge, as well as additional terrain to the east. The geometry of this observation is very similar to the high-resolution global color mosaic acquired during C21. At the time this observation was acquired, on December 18, 1996, this image provided the highest resolution imaging of Io's leading hemisphere and parts of the sub-Jovian hemisphere. The observation also revealed several changes between the September and December 1996 in this region, including new or changed plume deposits at Prometheus, Zamama, and at a volcano near 80 N, 100 W. This image was released by the Galileo Project as PIA00584.
Well, I guess E6 is next.
Link: Galileo Images of Io [pirlwww.lpl.arizona.edu]
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]
Tuesday, February 26, 2008
HERE BE DRAGONS...
Through your telescopes I am
merely a star, a spark of light that slides
and glides ‘round proud Jupiter;
one night here, the next night there,
sometimes with company, often alone
on Jove’s left or right. One of four
fluttering fireflies flitting silently through
the blush of the Red Spot’s glow.
But dare to approach me, to brave Jupiter’s
cell-scything rays and you’ll crave
the safety of Earth once more, for I am a world
where chemistry screams at the sky
and tears at your eyes, with claws
of colour so sharp and so raw
you’ll turn your face away and seek
the comfort of Callisto’s cratered smile.
For where my colder, older brother
and sister moons glow shivering shades of blue
and grey, my tortured face is painted hues
of fiery red; instead of frigid plains
of painfully pastel tones, my bones lie under
seeping fields of sores and blistering boils.
A pox-infected moon am I, a leprous satellite
that brings my smooth-skinned family shame.
Yet, if they knew my secret, the mysteries
I keep hidden from their disapproving
view, they would feel envy, for the tangerine-
and clementine-hued splashes on my
face are not mere volcanoes, as your
Earthly scientists believe, but are great blooms
and plumes of fyre, breathed out by beasts
which bathe beneath my Jupiter-racked crust.
Maui, Marduk, Loki – dragons all, and with
Volund and Pele prowl and crawl thru my sulphurous
churning seas; wings outstretched, tails sweeping
to and fro below my scabby-encrusted skin,
swimming, spinning, gorging on my
bitter bile before breaking through to spew
their flaming breath out into space in great
gushes of furious light. What a sight!
And what luck you had, sending one of your
nuts and bolts butterflies gliding past me
just as mighty Tvashtar roared, vomiting his
dragonfyre towards the stars, howling with
Masubi and Prometheus in a choir of dragons
singing to the Great One’s swirling storms;
what fortune to soar through this cloud of worlds
on your way to the Belt, and Beyond…
Anyways, so that article is on Wikipedia if you want to check that out.
Link: Main Page - Wikipedia, the free encyclopedia [en.wikipedia.org]
Monday, February 25, 2008
Gregg and Lopes, in their paper, point out a few problems with both models. In the first, wherein lava flows spread out from a fissure, the lack of overflowing lava despite repeated eruption episodes over the last 20 years is a concern. In the second, the difference in scale between terrestrial lava lakes (most are on the order of 100 meters across) and Loki (approximately 200 km across) is an issue. The authors point out several other issues, including the scale of magma reservoir needed and the thermally patchy nature of the patera floor.
The authors instead propose the following model for Loki Patera: 1) Magma is fed into a thin (10s-100s meters thick) chamber from a tidally heated source deep beneath Loki; 2) When this chamber is filled, magma travels up a conduit a few km long (assuming relatively low surface porosity) and into a fissure along the southwestern margin of the patera; 3) The lava then flows out from the fissure into pre-existing lava tubes or covered-over lava channels, travelling out from the fissure across the rest of the patera; 4) The lava ends up being intruded into the country rock of the patera floor (rather than flowing along the surface as lava flows) or fills lava ponds along the patera margin; 5) The eruption episode ends when the magma chamber is emptied and the lava in the fissure trench drains back down. The authors suggest that the eruption style at Loki is roughly analogous to eruptions along the East Pacific Rise.
This model is consistent with observations obtained of Loki. The thermal wave seen by ground-based observers and NIMS would be produced by heat conducted up from the lava tubes to the patera floor. The hotspot along the southeastern margin of the patera represents the location of the fissure. The other hotspots along the patera margin and along the margin of the "island" on the floor of Loki likely represent lava ponds where lava has collected at a topographic obstacle. The corresponding darkening wave at visible wavelengths seen along the patera floor by Voyager 1 and 2, rather than being the result of lava flowing across the surface or new crust in an overturning lava lake, is the result of volatiles being driven off a surface that is heated from below by lava flowing through lava tubes.
This is certainly a very interesting model for Loki as it explains the lower temperature measured by NIMS and PPR compared to eruptions at other volcanoes on Io and the lack of lava overflowing the patera margin. I think the lava lake model works best for smaller volcanoes like Pele and the southeastern portion of Gish Bar Patera, where the difference in size between terrestrial and Ionian lava lakes wouldn't be so great. It would be interesting to see how well this model might work for other inter-patera flows, like the main floor of Gish Bar or Emakong Patera.
Link: Lava lakes on Io: New perspectives from modeling [dx.doi.org]
The E26 observation from January 2000 is the highest resolution color observation from Galileo covering the trailing hemisphere of Io. This includes Loki, Daedalus, and the northern half of Pillan. This isn't a widely-known observation. As far as I know, the whole image was not released publicly by the project, though a composite showing color changes was available (I think).
I have been working on reprocessing Galileo Io images over the past year off and on. The images I have been posting over the last month have gone through the following processing steps:
- The raw images are downloaded from the Galileo Planetary Image Atlas Website
- These images are then converted from the original PDS format to the ISIS format. ISIS is a spacecraft image processing software suite produced by the Astrogeology department at the United States Geological Survey branch in Flagstaff, Arizona. The ISIS software package will definitely be the subject of future posts in the form of image processing tutorials.
- This step includes the pds2isis, gllfixlabel, and levinit procedures. These convert the original raw files to ISIS, correct the original labels to work with ISIS software, and apply geometry backplanes to the images, respectively.
- For now, the geometry applied by the levinit program assumes the default SPICE kernel files are correct (which may or may not be the case), but in general, since I've only reprojected one of these observations so far, any discrepancies haven't mattered.
- The ISIS procedure ssical is used to calibrate each image and to convert the pixel values from the 8-bit DN values to 16-bit I/F values. This allows me to ensure that each color filter image is scaled the same when I convert them to TIF and merged to create proper color images.
- The edges of each image are trimmed to remove edge effects.
- Several instances of the ISIS procedure boxfilter are run to clean up noise. Due to the enhanced charged particle environment at Jupiter (and Io in particular), bright pixels can show up at random locations. This steps helps to remove those pixels and fill them with an average of the surrounding pixels. The standard deviation used in boxfilter is adjusted (usually between 1.3 and 1.9) depending on the Signal-to-Noise ratio of the image. In general, close-up images of Io or images from later in the mission are noisier than distant images or images from earlier in the mission.
- The cleaned-up, calibrated images are converted to TIF using the ISIS procedure isis2tif. The images are scaled so that the pixel value 255 is equal to the brightest pixel in all three images used in a color composite.
- The images are then merged into a color composite or a mosaic in Adobe Photoshop CS. They are then rotated so that north is up.
Link: Galileo Images of Io [pirlwww.lpl.arizona.edu]
Early last year, my attention returned to Io thanks to New Horizons. I became interested in what had happened on Io since Galileo last looked at it in October 2001 before crashing into Jupiter in September 2003. After posting some analysis of the New Horizons LORRI images on the Unmannedspaceflight.com website, I was privileged to be a co-author on the Science magazine paper on the New Horizons results at Io. Also the year before, I co-wrote a review chapter for Rosaly Lopes and John Spencer's book Io After Galileo on that probe's mission at Io.
So over the last year, in my spare time, I've been drawn back to Io: reprocessing Galileo and Voyager images, working with the New Horizons images, and editing the Wikipedia article on Io. Now, a blog.
Wait, a blog about Jupiter's Moon Io? But there isn't a spacecraft within 100 million km of it!
True, but that doesn't mean that there is no news, new images, or potential discussion points about everyone's favorite moon. I plan on reporting on papers and abstracts that are released and explaining some of these new results. I will post some of my reprocessed images that I've been working on. If any readers are amateur astrophotographers (or professional, I'm not discriminatory), and you have some nice Jupiter-Io shots to share, pass them along. Got some new volcano news you like to share, I would love to hear it.
Obviously, since news is not being generated daily about Io, there will some off-topic posts, like movies I am enjoying at the moment or the latest Europa news to annoy me (hey, wanna be creative and make some nice anti-Europan propaganda posters, pass them along). Obviously, as a new blog, we'll see how this goes.
I hope you all enjoy!