The Long Mars

Terry Pratchett and Stephen Baxter

Baxter and Pratchett’s latest collaboration begins as a catastrophic eruption of the Yellowstone supervolcano forcibly accelerates emigration from our Earth to the thousands of ‘stepwise’ duplicates explored in the previous books.

But, as the title suggests, another new frontier has opened up too; conditions on some alternate Earths make space launches much easier, and Mars turns out to have stepwise duplicates of its own.