The Long Mars[1] is a science fiction novel by Terry Pratchett and Stephen Baxter.

It is the third in a five-book series of the parallel-Earth sequence The Long Earth.

[3] In the novel, Sally Linsay, her father, and a burned-out astronaut friend travel to Mars and find that it too has co-existing alternate worlds accessible to their technology.

While many are lifeless and possess atmospheres as thin as those of Mars within our universe, others possess oceans, life forms and intelligent life.

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