Landscape on the smaller of the two lobes of Comet 67P/Churyumov-Gerasimenko
taken from a distance of just 5 miles (8 km).
Image credit: ESA/Rosetta/MPS for OSIRIS Team
A series of scientific papers in journal Science published on January 23rd offers a complete, if preliminary, look at Rosetta’s comet. And what a wonderful and complex world it is.
Taylor & al. made an abstract of the articles that states that the surface of the comet shows evidence of many active processes and is highly complex. The solid nucleus is an object for which neither horizontal nor vertical variations are modest. He also says that the current comet shape model suggests that the mass is 1013 kg (about 100 million times the mass of the international space station), with a bulk density of ~470 kg/m3 (similar to cork, wood, or aerogel). The low mass and density values strongly constrain the composition and internal structure of the nucleus, implying a relatively fluffy nature, with a porosity of 70 to 80%". There is also some ideas about nucleus surface that appears rich in organic materials, with little sign of water ice.
It seems also that the coma produced by ices sublimating from the nucleus is highly variable, displaying large diurnal and possibly seasonal changes. (learn more)