UA Mars explorer to complete PhD 3 decades later

This probably falls under the 'better late than never' category - Inside Tucson Business reports today that,

"Peter Smith will receive his PhD from the University of Arizona, where he began work on his doctorate in 1975 but never finished at the end of May. The renowned scientist is responsible for all aspects of NASA’s enormously successful Phoenix Mission to Mars. The lure of hands-on research became irresistible, and he was talented enough to move forward without a PhD."

I wonder what his dissertation is about.