In the late 1970s, Saturn’s odd moon Titan, a hazy orange world, was expecting visitors — first, NASA’s Pioneer 11 probe, then the twin Voyager spacecraft. Most moons are airless or boast little more than gauzy, gaseous veils. But Titan is cloaked in a blanket of nitrogen and methane so thick that, with a pair of wings and a running start, astronauts on the frosty satellite could fly just by…
