The data being gathered by the European Space Agency probe is going to keep scientists busy for years, but it is clear already that many of the old ideas about how comets are put together and how they behave will have to change.
It is obvious now that this comet is not a large lump of ice with some dust mixed in. Rather, it has a much more complex construction, incorporating significantly more dust and many rocky components. This is very evident from the ratio of dust to gas being ejected by the comet (four to one), and all those craggy cliff features where stiff, consolidated materials seem to dominate.
"We used to think of comets as 'dirty snowballs'; we now think 'icy dirt-ball' is a much better description," said Simon Green from the UK's Open University. "That's the way 67P looks - a solid object with ice vaporising from somewhere below the surface."
Rosetta: 'Goosebumps' on 'space duck' hint at comet formation
Comets are icy dirt balls or snowy dustballs?
The new comet findings, detailed in a special issue of the journal Science this week, are even calling into question an old axiom of comet research. Many scientists have dubbed comets "dirty snowballs," but now it might be more appropriate to call this comet a "snowy dustball" because of its dust-to-gas ration, said Alessandra Rotundi, the principal investigator of Rosetta's GIADA dust grain analyzer instrument. Some comets might be "dirty snowballs," while others are "snowy dustballs." [See amazing comet photos from Rosetta]
"Comets appear to be quite different compared one to the other," Rotundi told Space.com via email. "This comet confirms that we would be wrong speaking only of dirty snowballs."
Strange Comet Discoveries Revealed by Rosetta Spacecraft