Johnson, Sarah Stewart: - Sarah Stewart Johnson is an associate professor at Georgetown University, where she teaches astrobiology and planetary science and leads a biosignatures laboratory. A former Goldwater, Truman, and Rhodes Scholar, as well as a Junior Fellow in the Harvard Society of Fellows, she received degrees in PPE and in Biology from the University of Oxford, and a PhD from MIT. She worked with President Obama's science advisor in the White House, and now serves on the science team for NASA's Curiosity Mars Rover.