Mark studies aerosols in planetary atmospheres via remote sensing and modeling. His long-time focus has been Mars: for Opportunity and Curiosity, he monitors atmospheric dust load, studies dust properties, measures dust lifting in dust devils, and moonlights in astronomical imaging. He is currently preparing for a similar role on Mars 2020 with Mastcam-Z and Skycam. Previously, he was the imaging team lead for the Phoenix mission, as well as a participant in Spirit's mission and a member of the imaging teams for Mars Pathfinder and (very briefly) Mars Polar Lander. In non-Martian studies since graduating with a PhD in Planetary Science from the University of Arizona in 1994, he studied Jupiter's clouds with the Net Flux Radiometer on the Galileo Probe, and Titan's aerosols with the Hubble Space Telescope and the Huygens Probe's Descent Imager/Spectral Radiometer.