The spacecraft flew past Titan on 26 October, getting as close as 1,200 kilometers from the moon's surface, which is shrouded in clouds and haze.
But scientists remain perplexed. Professor John Zarnecki is a member of the "Cassini-Huygens" science team at Britain's Open University.
"Mysterious. I have to say that Titan seems to be holding its mystery to the very last minute. There was part of me which thought that the fly-by last week would reveal everything, and there will be nothing left for us to find out. But, in fact, it seems it is as mysterious as ever," Zarnecki says.
Zarnecki says the data revealed outlines of peculiar dark and light features on Titan's surface, raising questions about their nature and composition.
"We've got the radar images; we've got the near-infrared images. Nobody still knows what the hell is down there. Is it a hydrocarbon ocean? Is it ice? Is it hydrocarbon gunge or goo-like tar? I think we still don't know. For me, what is odd is that in the images that we see, there are not many or no impact craters. The surface is active. There are things happening which are covering up or eroding," Zarnecki says.
Zarnecki also notes that some images show strange streaks, similar to ones observed on Mars which wind may have caused.
"There's one or two that certainly seem to indicate some sort of fluid flow. And what is the fluid? Is it wind as on Mars? Could it be liquid flow? Some people are saying it is ice flow, because ice, of course, does flow as a very viscous liquid, in a way," Zarnecki says.
Other scientists agree that many questions remain. But they point out that the spacecraft's close encounter has already provided some important data.
Titan's environment can finally be understood and compared to conditions on other planets. Dr. Andrew Coates is a member of the "Cassini-Huygens" team at the Mullard Space Science Laboratory at the University College London.
"We can see methane clouds which change in size, so that's indicating an active weather system involving methane. The radar instrument was able to look at 1 percent of the surface of Titan, and in that was a tantalizing glimpse of what could be liquid methane on the surface. The whole environment of Titan seems to be completely full of hydrocarbons," Coates says.
"Cassini" is expected to carry out 45 more encounters with Titan over the next four years.
But Coates says some remaining mysteries should be revealed during the next fly-by on 13 December, before the "Huygens" surface probe enters its murky atmosphere.
"The 'Huygens' mission will be released on Christmas Day European time [25 December] from the 'Cassini' orbiter, and then will land on 15 January. That then will give us the ground truth for these remote sensing measurements. Before that, we have another Titan fly-by with which we will be able sort of refine the models of what the surface is like. But, at the moment, we do not know whether the probe is going to land with a splash, a squelch, or a thump," Coates says.
Zarnecki points out that data about the density of Titan's atmosphere jives well with previous models that estimated it as being twice as thick as the Earth's atmosphere. He says that should help the "Huygens" probe to land safely.
However, the scientist says nothing can be done to steer the probe once it pierces Titan's methane atmosphere:
"If the surface turned out to be made of cheese, or marzipan, or whatever, there is actually nothing that we can change about the descent and landing," Zarnecki says.
Despite all these unknowns, Zarnecki remains confident the "Cassini-Huygens" mission will eventually reveal some of Titan's deepest mysteries.