Christopher McKay Develops “Extreme Checklist” For Habitable Planets

New Scientist (6/9, Grossman, 329K) reports that Christopher McKay of the Ames Research Center has developed an “expanded checklist” of the types of planets that could host life. The new checklist was based on “the extremes that life can endure” here on Earth. McKay cautioned that Titan, with its surface liquid and weather cycle based on compounds like methane and ethane instead of water, “there are perhaps more things in heaven and Earth than we can imagine, as Hamlet said. It’s a cautionary tale. … If we discover something new, we will have to rewrite this chapter.”