"Thompson Heller: Detective Interstellar" is a story about a private detective who wanders the stars solving cases with a political or moral dimension.
Heller is a smart, funny, hard-drinking smartass. He's a skeptic/atheist. Speaks many alien languages. His primary accessories are his smartscanner device, which floats magnetically a couple inches above his finger, as well as a glass of whiskey or a cigarette.
The logo should most likely give some prominence to "Thompson Heller" and then a slightly less emphasized "Detective Interstellar". But the difference between these two elements should be minor. Like the difference between bold and normal font weight if there's size difference, not TOO big a difference.
Whether or not you choose to put a colon between the two words, is purely up to the design choice, but I think it'll probably be more balanced if you just separate the two with other visual means and avoid using the colon. Our temporary logo just has Thompson Heller in bold, with Detective Interstellar directly underneath in normal font weight.
The first page in the PDF is a sample/temporary cover. However, the colors/layouts of other covers might vary substantially. The logo should be flexible to be adjusted for color/contrasts and different contexts.
For further research/reference, check out comic book covers for recent series published by Image Comics or Vault Comics. A great example would be "Black Science" from Image Comics.