Turtledove, Harry. A World of Difference
Divergence: c 4,500,000,000 BCE
What if: The formation of Mars resulted in a larger planet, capable of sustaining a thicker atmosphere and surface water.
Summary: After a tool-bearing lifeform destroys a Viking probe on the surface of "Minerva", competitive American and Soviet manned missions are sent out.
Comments: Synopsis in Gerson Lodi-Ribeiro's "Histórias Naturais Alternativas", q.v.
Published: Ballantine/Del Rey 1990/2005 (0345360761BUY); Hodder & Stoughton 1998 (0340712708), 1999 (0340712716BUY); New English Library 1999 (0340712716).
Original in: English.
Translation: Italian by Carlo Borriello as Missione su Minerva, Fanucci 2000.
Translation: Russian as Bitva v Kosmose, Armada 1997.