32. Land & Overland
Interplanetary travel... by hot air balloon!
In Bob Shaw's 'Ragged Astronauts' trilogy, the planets of Land and Overland are separated by a mere few thousand miles, and their atmospheres interact. This is a great setting for some exciting fiction. Felix Baumgartner would take a lot longer to fall to Earth if another planet was pulling him upward with almost the same force as Earth was pulling him downward.
These books are curious in many ways and worth a read - although the authors 'Other Days, Other Eyes' is even better. I couldnt think of how to illustrate that one for this series though.