As a geologist and geophysicist, Phil Christensen's research interests focus on the composition, processes, and physical properties of Mars, the Earth, and other planets.

Christensen is a professor in the School of Earth and Space Exploration and has built five science instruments that have flown on NASA missions to Mars. His discovery of crystalline hematite in Meridiani Planum was instrumental in that area's choice as the landing site for the Mars Exploration Rover Opportunity. He was awarded NASA's Exceptional Scientific Achievement Medal in 2003 for his pioneering scientific observations of Mars in the infrared.