Measuring comet 67P/C-G

http://blogs.esa.int/rosetta/2014/10/03/measuring-comet-67pc-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.

Shape model of 67P/C-G. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Shape model of 67P/C-G. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

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.

 

Comet 67P/C-G dimensions. Images: NAVCAM; dimensions: OSIRIS

Comet 67P/C-G dimensions. Images: NAVCAM (19 August image); dimensions: OSIRIS

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
Rotation 12.4043 hours OSIRIS
Spin axis Right ascension: 69 degrees; Declination: 64 degrees OSIRIS
Mass 10^13 kg RSI
Volume 25 km^3 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)