The MSL Siting Decision

On July 6, NASA announced it had narrowed the number of sites where MSL might land to two. They were both craters: Gale and Eberswalde. In making this decision, NASA dropped two others in the “final four”: another crater named Holden and a likely flood channel called Mawrth Vallis. While all four provided evidence of ancient water activity, the two finalists were especially intriguing.

Eberswalde was believed to be an ancient river delta. Gale Crater contained a mountain in its center. If Gale became the final choice, MSL would climb part of the way up this mountain, studying different layers of rock as it went. NASA said it would choose the final site by the end of July. Grotzinger, MSL’s lead project scientist, declared at a press conference, “It’s like two different flavors of ice cream—do you like the chocolate or vanilla on Mars? So we go back and forth a lot.”55 Weiler told Grotzinger, “John, I want to you to go as if this is the last Mars mission for 50 years. Find the best place to go.”56 Grotzinger got the top MSL managers and scientists together in a proverbial “smoke-filled room.” They came down unanimously in favor of Gale and recommended this site to Weiler.57 Weiler made the choice official, and it was announced on July 22.