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The Planetary Society BlogBy Emily LakdawallaDoug Ellison at Europlanet 2008: Arrival and Mars' north poleSep. 22, 2008 | 11:27 PDT | 18:27 UTC
All this week, Doug Ellison will be filing reports from the third European Planetary Science Congress, also known as Europlanet, taking place in Münster, Germany. Doug is the dictator-for-life of the online forum unmannedspaceflight.com. Thanks, Doug! --ESL by Doug Ellison Another year, another Europlanet. This time it's in the northwest German city of Münster, at the Westfälische Wilhelms-Universität (that's the University to you and me). It's a stunning venue, somewhat compromised by the large tent erected to house the poster sessions.
As you will have heard Emily and me both lament from conferences before: until we figure out how to clone ourselves, we can only see on session at a time. Europlanet this year runs five sessions concurrently, so four-fifths of the content immediately flies out the window. Because of that, and because of my bias toward presentations on subjects that find interesting and I think I can blog about, I would urge you to review the abstracts at the EPSC Website. Two-page abstracts abound, and in some cases cover every ounce of information that will be presented in the oral presentations anyway. I'm going to try and pick one or two presentations each half-day, and blog those. On Wednesday are the Outreach sessions, in which I'm presenting on the outreach done by the Mars Exploration Rover team that the amateur community has leveraged into what I call ‘Bootleg Postcards'. I picked "Mars Polar Deposits and First Results from Phoenix" as my first session. However, there were no Phoenix results at all. Truthfully, I don't expect the good stuff from Phoenix to make it out to conferences or publications for another few months. However, Kathryn Fishbaugh presented a paper on northern polar deposits that have more than a little to do with a pertinent terrestrial topic: climate. The polar caps are links to climate and atmosphere. They are records of recent climatic change. To understand that record we need to understand the layers, but this quickly raises two interesting points. Firstly, a layer is itself defined by the method used to observe it. Layers seen in radar may or may not be the same as layers seen in imagery. Layers seen in Viking orbiter imagery show large stripes, but imagery from [Mars Global Surveyor] MOC and [Mars Reconnaissance Orbiter] HiRISE shows some of these stripes to be a collection of many stripes themselves. Secondly, when we see imagery, is the brightness due to the inherent albedo of the material in question, or the illumination it is receiving, or the slope on which it is found? This is especially pertinent on the steep slopes where the polar layering is found, as there are lots of elevation changes involved, which can affect the apparent brightness of the layering. To back out from the elevation, they have generated a digital elevation model from HiRISE imagery, similar to that which I used to animate the Columbia hills a few months ago. Randy Kirk, from the United States Geological Survey, has been producing elevation models from pairs of orbital images for some time with great results from MOC, and now HiRISE. With this one-meter-scale elevation model, they can calculate out the impact of illumination on the terrain and produce a map of actual surface brightness. This raises one point at which care must be taken. Because (although this is not an especially good analogy) in many places the shape of the layers replicates ripples one might see on a sea bed, one must ask: are we looking at actual layering, or something else? To truly ensure they are looking at layers and not localized erosion features they take tracks thru the layers and average out multiple tracks taken at several locations on the same slopes. Genuine features will then stand out above the local noise floor caused by erosion. But at HiRISE's highest resolution of 30 centimetres per pixel resolution, the layers are not sharp-edged. This means we either have layers that have gradual transitions, or there is a thin localized mantle of dust and ice that blurs the contacts between layers. This means we have a human element to the measurement of the layers. When different people measure the layers, they get thicknesses between 5 and 10 metres (so that's a human error of ±2 meters), with layers 20 to 30 metres apart.
Two current models that take into account the precession and obliquity of Mars begin to match the pattern of marker beds and smaller layers, but neither match them especially well, giving different ages for the layering of between two and ten million years. [Tying variations in ice layer thickness to variations in orbital parameters has been done successfully for Earth; Google "Milankovitch Cycles" if you want to read more about that. --ESL] Tying the layering to orbital parameters isn't going to be straightforward, so future work involving details of stratigraphic columns and especially the linking of marker beds to radar layers seen by [Mars Reconnaissance Orbiter] SHARAD and [Mars Express] MARSIS will be essential in pulling the story apart and understanding what the layered deposits of Mars are telling us. That's all I managed to get of the morning session - but I thought I'd finish each blog entry with a random paper from EPSC just to demonstrate the diversity of what's being presented. The first one is guaranteed to save the eyesight of grad students everywhere: a Portuguese group's presentation on automated crater counting techniques (PDF, 576k).
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