William Hartmann is an American planetary scientist known for his work in the fields of planetary geology and astrobiology. He has contributed significantly to our understanding of the Moon, Mars, and other celestial bodies through his research and publications. Hartmann is also recognized for his role in the development of the Mars Exploration Program. In addition to his scientific research, Hartmann is an accomplished author and has written several books aimed at educating the public about space science. His work often emphasizes the importance of exploring other planets and understanding their potential for life beyond Earth.