London: It appears that the Rosetta's comet 67P is grey in colour like many small bodies in space, it has been reported.
The images obtained by Rosetta's scientific imaging system OSIRIS after careful processing led to the conclusion that most of the comet's part was even more dark and grey than expected.
To create an image revealing 67P's "true" colours, the scientists superposed images taken with the camera's red, green and blue filters.
The imaging system was equipped with several colour filters allowing only light within a limited range of wavelengths to pass through. As a result, the intensity variations seen in OSIRIS images are based only on a small part of the Sunlight reflected by the comet.
During the sequence of photos, as each filter was brought into play, both the comet and the Rosetta space craft were moving, so the three images were slight shifted in their perspective and had to be painstakingly worked on to create an accurate superimposition.
At the same time, first analyses showed that Rosetta's comet reflected red light slightly more efficiently than other wavelengths. This phenomenon had been well-known from many other small bodies and due to the small size of the surface grains. It does not, however, mean that the comet looks reddish to the human eye. Since in natural sunlight red components are slightly suppressed, to the human eye both effects together create a greyish appearance.