Robin Sherman says:
19/12/2014 at 01:03
Having seen all the presentations that were actually shown, four are still not viewable and one was cancelled, I thought I would outline the key things that were common conclusions. A lot of results just defined boundaries or the range of results and some did not match existing models or experimental data closely enough to give exact conclusions. The majority of the Philae reports amounted to a list of what data was collected and how they might be able to use it.
The Northern "Duckiesphere" currently in Summer is way more active than the "Dark Side". The detection of metal ions like Sodium, Magnesium, Zinc, Iron is limited to nighttime observations and is thought to be due to sputtering from the Solar Wind and Cosmic Rays.
They are not seen during the day, because cometary activity produces a coma containing gas, ions, charged particles and dust that physically and magnetically shields the surface from the Solar Wind.
Activity is directly correlated to the amount of sunlight incident on a surface, but the neck areas and the north polar plain are more active than the head and body lobes due to a thinner layer of insulation. These more active areas contain fewer organics. The majority of the surface layer away from the active regions contains between 5 and 7% organic material, with the highest amounts on the sides of the lobes where there is a lot more exposed solid material. The nature of the organics is still not known, one fit to the data suggests a mixture of a neutral black material with 99.5% Tholins and 0.5% Water. Another result suggests that it is not all Tholins and is likely a mixture of Carbon, Tholins, Low Iron content silicate minerals and various Sulphides.
The consensus seems to be that in the flatter plains where the surface appears to be covered in a dust blanket, like at the first touchdown point, there is a top ice free layer of friable, porous, gravel and dust about 1cm thick made up of low iron minerals, silicates, organics and Carbon. Below that the material starts to contain volatile ices, the amount increasing with depth. This mixed ice/dust/organics layer varies, but is estimated to be 10 to 20cm normally, but may vary. Beneath this is a hard layer of sintered ice/dust/organics, which although hard is also brittle as evidenced by the shards seen in the ROLIS images.
Sulphur is present in significant amounts and is usually found in the areas where Water is coming from, but also from a few areas where very little Water is seen. Although visually the comet is pretty homogeneous, chemically it seems not. Water tends to be produced in very variable amounts related to the time of day and position on the comet, whereas Carbon Dioxide emission seems to be more constant. The ratio of CO2/H2O is on average about 7%. The thermal properties of the top dust layer suggest up until now outgassing is not coming from the harder sub surface layer.
The CONSERT talk was limited and the second one cancelled, presumably because Philae has not been located. The data is clear and of good quality, but the only conclusion is that the shape of the signal peak indicates very little or no scattering from internal surfaces, meaning the comet is not currently made up of metre or two sized planetesimals, but is a continuous solid.
Organics that have been identified include C2, C3, C4 compounds and Benzene. Other results indicate Amines, Benzoic Acids, Ketones and Esters are probably present as well. Dust particles from the comet are larger than expected, but are very irregular, conglomerates of very loosely bound material which falls apart on contact. More solid grains have been examined which although only micron size look like mini comets, with planes, pits and holes. They have also been seen to move once trapped in the instrument. This was explained as being their light weight, but sublimating gas creating a frictionless layer underneath them likely helps.
The surface layer at Agilkia was revealed in all it glory by the ROLIS images. Hopefully those images will be available here soon. This was the most informative and revealing presentation shown. Analysis was done of the particle sizes and the surface seems to be made of a sort of pea gravel 1 or 2 cm in size with larger pieces of broken cryorock mixed in. Hollows and depressions around a metre in size along with small ledges and elevation changes in the 10s of cm range. Little tiny landslides of little pebbles, but little sign of dust except at the base of the 5m Cryobolder close to the touchdown point. It would appear that the surface layer material is very much like a type of aerogel, it holds it shape perfectly until disturbed and then just disintegrates into a fine powder. This is what was seen in both MIDAS and COSIMA. Unfortunately the dust measuring device on Philae has so far only registered 1 confirmed hit.
The team seem even more confident that Philae will survive and be able to do more science. It is clear from these presentations that there is lots of revealing data available, there are vast amounts of it and much of it requires some new algorithms and models to interpret, especially the Philae data. An amazing job by everyone involved. I should also add that the speakers were way more entertaining and interesting than many of the others here.
So most of what we learned in the presentations that were shown, had already been deduced by ourselves or explained by team members here and this just added confirmation that many peoples combined educated guesses were right. The talks showing OSIRIS data and explanations of the comet morphology were not streamed and information from the plasma and magnetic field experiments were not shown. Hopefully some sort of apology or explanation from the ESA team will be forthcoming to explain this.
