Jules Verne's Series

OK. I got it wrong again. See here. Three Jules Verne novels form a trilogy:

From The Earth To The Moon
Around The Moon
The Purchase Of The North Pole

- two form a diptych:

To The Sun?
Off On A Comet
(Later: it transpires that these books are a single novel translated and published in two volumes.)

- two feature Captain Nemo:

Twenty Thousand Leagues Under The Sea
The Mysterious Island
and are connected by other characters to In Search Of The Castaways

- and I suspect that there are other connections between Verne's books of which I am as yet unaware.

Wells' two interplanetary novels follow Verne's and also in the same literary tradition are CS Lewis' Out Of The Silent Planet and Perelandra/Voyage To Venus. The third volume of Lewis' trilogy, That Hideous Strength, continues the tradition because, although it is set entirely on Earth, it places Earth in a Solar context and imparts information about life on the Moon. However, it is mainly a reply to Wells' The Shape Of Things To Come and Olaf Stapledon's Last And First Men because it addresses the question of the social role of science in the future of human civilization on Earth.