This morning, Pamela and I traded subjects – I went to the session on Mars, while she went back to the session on the Moon.

This session was about 10 feet over my head – but we’ll see what I can do to tell you about it.

The first talk I heard was probably the most understandable, and the one I have the most complete notes for. Low Thermal Inertia and High Elevation Bedforms as Seen by the HiRISE Camera (Bridges, N.T., Gorbaty E., Beyer R.A., Byrne S., Thomson B.J., Wray J., HiRISE Team)

This group was investigating low thermal inertia and high elevation bedforms as seen by the HiRISE camera. They were looking at the Tharsis and Elysium summits in particular, which have also been imaged by the Viking orbiter.

The Viking images show that these volcanic summits have low thermal inertias consistent with a surface coated by a fine (2-40microns) particulate, and having a bright albedo of greater than 0.27. The images also show dark collars surrounding the centre of the volcanoes and the presence of downslope wind streaks at their bases. This is probably from downslope winds induced by nighttime cooling.

So, they presented a few hypotheses:

High elevation volcanoes act as sinks of Martian dust that settles on to the surface after large dust storms. Low pressures and there for lack of sufficient shear stress to liberate significant dust off the surface allows accumulation. Some surfaces are subjected to Aeolian transport.

Based on the Viking images, before HiRISE, these were their (faulty) predictions:
- the surface would be fairly featureless
- some wind features would be visible
- no bedforms would have been formed from saltation, because the particle size and atmospheric pressure is too low for saltation ,and winds that liberate material must be high, and they’re not.

This interpretation is wrong.

This group did a very detailed analysis, looking at 100 HiRISE images of tharsis and Elysium. They looked at coverage, shape, and size of the bedform, as well as MOLA and THEMIS thermal inertia data. Google Earth provided qualitative comparisons among data sets.

So, what did they find?

Well, reticulate bedforms are almost pervasive on volcano flanks and calderas, but much less common in the intervening plains. They form in areas of low thermal inertia with a variety of elevations, including the highest.

These bedforms have up to three orders of scale: 1-2m, 15-20m and 50-200m (though the last may be an underlying topography). There are two dominant “textures” – the honeycomb texture, which has star bedforms on craters and pits, and the accordion texture – linear with first and second order bedforms on the plans.

There is evidence for migration of material downslope, rather than accumulated, static dust. The bedforms are found in patches and are concentrated in radially downslope direction from caldera. Other areas near the caldera have a very high concentration of craters. These Aeolian features are not made of true basalt, but it might be dust aggregates.

Finally, the group hypothesises that the dust aggregates start small and grow in size, or they are small but not cohesive. It’s still hard to saltate without suspending the material. The terminal speed is proportional to the particle size at saltation/suspension boundary, so small particles become suspended.

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That was really the only talk I was able to come close to understanding. There were a couple of cool ones that really require pictures to discuss in a useful manner. Unfortunately, I think it’s the engineer in me that thought they were cool.

Laboratory Studies of Dust Devil Sediment Flux: Comparing with Data from Gusev Crater, Mars (Neakrase, L.D.V., Greeley R)

This group is using the Arizona State University Vortex Generator to try to study Martian dust devils. They had some really neat pictures of vortexes they’d created where they used CO2 to allow the form to be seen and photographed. When placed next to photos of Martian dust devils, you can really see the similarities (though the lab-made vortexes are much smaller).

By creating these vortexes, the group is studying their parameters – the roughness of the material being added, the change in mass per change in time, etc. They had lots of graphs that displayed their results in ways that I’m sure made sense to people who have even some training in that field. I thought the setup was pretty cool though.

There was another group who is studying the formation of Martian gullies by attempting to recreate them in a lab.

Simulation of Martian Gullies Using a Water/Ice Slush (Coleman K.A., Dixon J.C., Howe K.L., Rowe L.A., Chevrier V.F.)

They have created an experimental apparatus that allows them to create slopes of smoothed sediment/sand which they then add either water, or a water/ice slush to through a hose at the top of the slope.

They studied three different slopes of 10, 20 and 30 degree inclines, and measured the length, width and depth of the resulting channels before comparing their findings for water versus a slush.

They observed with the slush, they got levees (which did not appear with water). As the levee height increased, flow increased, which in turn built more levee. Channel length increases as flow length increases. The alcove width increased with increasing slope, which makes sense – steeper slope means more sheer forces to pull the alcove away.

The slush alcoves get narrower down slope, where as the water alcoves grew wider, making the slush alcoves a very good comparison to those of the gullies on Mars.

Again, they had quantified their data in ways that were well beyond me, but the general conclusions were that slush comes much closer to creating gullies that are similar to those we see on Mars. The group says their next steps are to experiment with smaller sediment sizes, permafrost layers, etc.

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