This paper examines the roles played by instruments and their associated practices in the development of the field of planetary geology. Specifically, remote sensing instruments and the images produced by instrument users are discussed. It is argued that through these instruments and images the first two generations of planetary geologists were able to 'domesticate' the planets and make them suitable for geological study. But this was not a straightforward process. The instruments themselves had to be 'domesticated' as geological tools, and (...) the definition of 'geologist' had to be broadened to include such tools and extraterrestrial terrains. This paper looks first at the first generation of planetary geologists associated with the mapping and study of the Moon in the 1960s and 70s, then focuses on the second generation that emerged during the exploration and mapping of Mars. Within this second section, the paper focuses on the introduction of one new type of instrument -- the orbiting infrared spectrometer, and examines three such instruments and the visual claims made with its images. (shrink)