They were selected, along with about a dozen international scientists, from a pool of 149 applicants based on their potential contributions to the scientific objective of the mission—to use the car-sized Mars rover, Curiosity, and its suite of scientific instruments to search for evidence of a once or presently habitable environment on Mars.
"The Participating Scientist program for MSL was extremely competitive," says John Grotzinger, the mission's project scientist and the Fletcher Jones Professor of Geology at Caltech. "It's great to have Ken and Bethany join the science team. Ken will bring unique expertise to the mission bearing on the age determination of rocks and geomorphic surfaces that we will encounter. Bethany's selection ensures that we are able to integrate her experience with orbiter-based spectroscopy with ground truthing of mineral compositions by Curiosity."