Latest images of Saturn's moon, Titan, show that the highlands of Titan may be full of caves. The highest mountains so far found on Titan are Xanadu, radio waves bouncing off suggest that it has peculiar electrical properties – specifically a low dielectric constant.
The only reasonable material makeup that could have a very low dielectric constant and still hold together enough to form the structures that we see would be some sort of porous stuff – most likely porous water ice." (Steve Wall of NASA's Jet Propulsion Laboratory in Pasadena, California, US.)
