TUCSON, Arizona—Two new "magic islands" have joined one reported last year on Saturn's giant moon Titan, Cassini spacecraft observations showed on Monday. The features add to a puzzling vanishing act playing out on the frozen world's seas.

Since Cassini first arrived at Saturn in 2004, its photos of Titan have revealed numerous seas, lakes, and rivers on the giant moon's frozen surface. This summer, images showed a mysterious feature in one sea—the first "magic island"—that appeared glinting on a lake's surface and then quickly vanished. (Related: "Waves Discovered on Saturn's Moon, Titan?")

The find raised speculation that scientists had captured views of waves splashing within the otherwise mirror-smooth liquid methane seas on the moon. Or else it was a fluke.

Now, an