The unusual shape of comet 67P/Churyumov-Gerasimenko, as recorded by the Rosetta mission, has led to much speculation about its origins. A simulation published in March 2018 in Nature Astronomy suggests that the comet could have formed when two comets collided, and furthermore that such a collision even at quite high speeds would have left the constituent parts largely unaltered (no large rise in temperatures or pressures). This is important because it means that whenever Churyumov-Gerasimenko actually took its current shape, we can still draw conclusions about primordial material from the origins of the solar system using Rosetta results.
Scientist Raphael Marschall from the MiARD project recently gave a talk to the Bern section of the ‘Astronomy on Tap’ movement that seeks to provide popular science talks with an astronomy theme to the general public in an informal setting. A video of his talk can be seen here, in which he summarises the reasons for studying comets, and his own research using results from the ROSETTA mission.
Within the MiARD project, the team members at Heriot-Watt University on Scotland are using terrestrial rocks as analogues for the porous material expected at the cometary surface when they carry out numerical simulations of gas flow through such porous material.
The link below is to a file from an X-ray computer tomography or ‘CT’ scan of a porous rock. (On some platforms the file will be viewable in your browser, on others you will have to download the file and use a viewer for .stl files, such as ‘Preview’ on Macintoshes or ‘Meshlab’ on Macintosh, Windows or Linux platforms.). The image is taken from the same file, and shows the extremely high porosity of this rock sample. Estimates of the porosity of the cometary surface vary, but it may be as high as 75%.
This GIF animation shows the comet using shape data from the ‘MTPD009’ model derived during the early part of the mission using images from the NavCam navigational camera instrument. To make the video (using the Unity programming tool), we had to lower the resolution of the model by a factor of ten. Watch this space for a version that will work with virtual reality glasses in 3D.
The MiARD project will produce higher accuracy, higher resolution shape models using images from the OSIRIS camera instrument, and will release them to ESA’s database for public access. A preliminary ‘SHAP2’ model from the early stage of the mission is already public.
The shape models can be downloaded from the Planetary Science Archive of the European Space Agency – follow the ‘SHAPE’ link in the right-hand sidebar, and log-in as a guest user when prompted. More information on what a shape model is, can be found in this ESA blog entry.