Saturn’s moon Titan is big enough to see in a small telescope. It’s a tiny fleck of light that seems to be swinging on an invisible thread in the blackness, surprisingly distant from lustrous Saturn. It’s a picture that can burn like an afterimage into the screen of your mind.

Titan was first identified by Christiaan Huygens in 1655. For a long time so little was known about it that it was more or less a blank, like most of the rest of the small bodies in the solar system. In the 1960s and ’70s, the exploration of space got mechanical feet, and in the early 1980s the Voyager spacecrafts cruised past Titan taking pictures.

Titan is completely shrouded in a thick orange smog, which is strange – few moons in our solar system have any atmosphere at all. But Titan’s cloud envelope is so thick that its inner atmosphere and surface are invisible from above. Readings showed the atmosphere was 99 percent nitrogen, with traces of hydrocarbons such as methane and ethane. This was intriguing to planetary astronomers because it implied Titan might be similar to primordial Earth, where life spawned, but much colder because it’s roughly 880 million miles farther from the sun – but still, a possibility.

The Voyager data created more blanks than they filled, really. What was under that shroud of orange smog? Could Titan be covered by an ocean of liquid methane? If so, what was at the bottom? And was anything living there?

Few advances in Titan knowledge were made until the Cassini spacecraft sailed into orbit around Saturn in 2004. Even then, more pictures disclosed more indefiniteness.

Then in January 2005, Cassini dropped the Huygens probe down through Titan’s clouds. Huygens sailed out from under the smog into a hazy, windy, orange-lit sky. It took pictures of the surface that suggested liquids did exist, possibly methane seas, and channels that looked like erosion paths suggested something might be flowing.

Huygens hurtled down, stopped on the surface, and after 21/2 hours perished as planned when its batteries gave out. The plain where Huygens still sits silent is strewn with rocks and boulders bathed in dusky, orangish light.

In a way it was all the same whether you looked down from above the opaque clouds or up from the barren surface: uncertainties. Huygens’ pictures cast doubt on the theory of the methane seas. Other completely unexpected readings implied that Titan may generate an extremely low-frequency radio wave.

Only the Earth is known to generate ELF waves, but they’re triggered by lightning, and there’s little evidence so far that lightning exists on Titan. (If it did it might ignite the flammable hydrocarbons – except it can’t because there’s no oxygen to feed a fire.) The waves could be bouncing off an underground ocean. But so far these speculations are just gropings in the dark – no one knows what’s going on.

Recently the Cassini spacecraft, still whirling around Saturn, sent back radar images of Titan that seem to depict shorelines after all. It looks like there are methane seas to be sailed, islands to be explored, mile-high mountains to be climbed, and methane snow on their peaks. Microbes might be living there. How any of it formed can only be imagined.

Close your eyes and that threadless fleck of light still burns there in the dark, playing on your mind’s eye as if gleaming through layer after layer of veils.