Vonnegut's inclusion here stems from a single work, The Sirens of Titan.
The action ranges from Earth to Mars, Mercury and Titan. Nevertheless, the reader coming to this book after Vonnegut's other work might well have low expectations of any colourful OSS stuff even in a book with ample space travel.
After all, this author is known mainly as a satirist.
And indeed The Sirens of Titan runs true to type - the book is mainly a satire. To be more precise, it's a witty attack on mankind's habit of equating luck with providence.
So the reader will not be surprised to find that the Mars episode is hardly Martian at all, except purely as a plot-convenience; we are given no feel for Mars as a world. The place almost might as well be some secret hide-out in a desert on Earth - but for the farcical reference to "oxygen pills"...
And yet, and yet -
The Mercury scenes are a quite different matter.
The planet Mercury sings like a crystal goblet.
It sings all the time.
One side of Mercury faces the Sun. That side has always faced the Sun. That side is a sea of white-hot dust.
The other side faces the nothingness of space eternal. That side has always faced the nothingness of space eternal. That side is a forest of giant blue-white crystals, aching cold.
It is the tension between the hot hemisphere of day-without-end and the cold hemisphere of night-without-end that makes Mercury sing.
Mercury has no atmosphere, so the song it sings is for the sense of touch.
The song is a slow one. Mercury will hold a single note in the song for as long as an Earthling millennium. There are those who think that the song was quick, wild and brilliant once - excruciatingly various. Possibly so.
There are creatures in the deep caves of Mercury.
The song their planet sings is important to them, for the creatures are nourished by vibrations. They feed on mechanical energy...
The entire Mercurian episode is an inspired piece of pure OSS Golden Age invention. For more about the music-eating Mercurian life forms, the "harmoniums", click here.
As for Titan itself - the world in the book's title - this will be dealt with on the Titan page.
Kurt Vonnegut, The Sirens of Titan (1959)