The European Space Agency's Rosetta spacecraft, which had been trailing Comet 67P/Churyumov-Gerasimenko in close range since August this year, has been taking black and white photos of its target comet.
The team behind the spacecraft's scientific imaging system OSIRIS, however, has finally produced a color image of the comet as it could be seen by the naked eye. Scientists were able to come up with the true color image by superimposing a combination of images that were taken through green, blue and red filters.
The resulting image, a combination of three images taken by OSIRIS on Aug. 6 while Rosetta was 120 kilometers away, could have been more exciting if 67P/C-G were characterized by more colorful hues just as how the Earth looks when viewed from the moon.
Unfortunately, the comet mainly has a dull color. Just as scientists have expected, the comet is very gray and only has subtle color variations on the surface, so the color photo turned out not very different from the earlier black and white renderings of the comet.
Scientists have long suspected of 67P/C-G's color because even before Rosetta began its rendezvous with its target comet; observations made using ground-based telescope show that the comet is gray on average. At the time, however, scientists could not resolve 67P/C-G and see its surface in detail.
With Rosetta's OSIRIS taking images of the comet in close range, scientists found that the comet's body is extremely homogenous in color. They were surprised that even on a detailed scale 67P/C-G's surface has little compositional variation.
The image, however, adds credence to some of the observations made by Rosetta's instruments. Ice on the surface should look brighter in the blue filter and thus lead to bluish patches, but the new color image does not show any indication of such icy patches, which is consistent with the observations made by the instruments on board the spacecraft.
The ESA said that the overall gray color of the comet's surface indicate that 67P/C-G is covered by some kind of dark dust, and additional data from OSIRIS could hopefully shed light on the composition of the dust. The space agency also said that OSIRIS will attempt to detect various gas species in the coma enveloping the nucleus.
"Further studies using other combinations of the 25 filters in OSIRIS' arsenal will focus on trying to understand the composition of this dust, by looking for different minerals such as pyroxenes, common in the Earth's crust, or minerals containing water," the ESA said.
