A 54-pound (25-kilogramme) rock. Estimated auction price: $2 million to $4 million. Why so expensive? It's the largest piece of Mars ever found on Earth. Sotheby's in New York will be auctioning what' ...

A 54-pound (25-kilogram) rock with an estimated auction price of $2 million to $4 million. Why so expensive? It’s the largest ...