We have been astonishingly successful in gathering knowledge about certain
objects or systems to which we seemingly have extremely limited access. In
light of this success, what are the methods through which we have come to
have this knowledge, and what are the limits of what we can know using these
methods? Traditionally, philosophers have viewed the methods that
scientists use in the investigation of limited-access systems as being
hypothetico-deductive. I argue that these methods are better understood by
thinking of what scientists are doing as gaining access to the previously
inaccessible parts of these systems through a series of indirect
measurements. We obtain a clearer picture both of what we can know with
confidence about limited-access systems, and the limits of this knowledge.
I illustrate this way of thinking about the epistemology of limited-access
systems through an examination of planetary astronomy and geophysics.