Posted on 03/10/2014 by emily
Measuring comet 67P/C-G
This post provides a summary of some of the essential physical parameters of Comet 67P/Churyumov-Gerasimenko, as measured by Rosetta ahead of and since its 6 August rendezvous. This is an on-going process and the numbers will be updated as newer data are obtained, analysed, and made available.
One of the key things is the so-called “shape model”, meaning a 3D model of the comet based on images from the OSIRIS and NAVCAM cameras. In a previous post we showed a render of one of the first shape models derived from OSIRIS data. Here we are releasing a more recent OSIRIS shape model in .wrl and .obj format, suitable for loading into 3D graphics applications (click the links to download).
A render of this shape model is shown at the top of this page, while the image below shows a pair of NAVCAM images to illustrate the sizes.
Because roughly 30% of the ‘dark side’ of 67P/C-G has not been resolved and analysed fully yet, the shape model is very incomplete over those regions. As a result, some of the derived parameters for the comet are only best estimates at present. These include the volume and the global density, the latter depending on the mass and the volume.
The table below summarises the approximate dimensions of 67P/C-G and other known parameters derived from observations made by Rosetta, with the instrument with which the measurement was made also indicated. Links are provided to earlier posts where some of these numbers have been previously presented.
Again, these values are preliminary and will likely change as the mission progresses and more data are available, and as the comet itself changes as it moves closer to the Sun. Similarly, other parameters such as the albedo of the comet will be added to this table, as they are made available by the instrument science teams.
|Dimensions (small lobe)||2.5 x 2.5 x 2.0 km||OSIRIS|
|Dimensions (large lobe)||4.1 x 3.2 x 1.3 km||OSIRIS|
|Spin axis||Right ascension: 69 degrees; Declination: 64 degrees||OSIRIS|
|Density||0.4 g/cm^3||RSI / OSIRIS|
|Water vapour production rate||300 ml/sec (Jun 2014); 1–5 l/sec (Jul-Aug 2014)||MIRO|
|Surface temperature||205–230K (Jul-Aug 2014)||VIRTIS|
|Subsurface temperature||30–160K (Aug 2014)||MIRO|
|Gases detected||Water, carbon monoxide, carbon dioxide, ammonia, methane, methanol||ROSINA|
|Dust grains||A few tens of microns to a few hundreds of microns||COSIMA
(detections also by GIADA)