Image resolution and evaluation of genetic hypotheses for planetary landscapes

The spatial resolution of image data tends to constrain the horizontal leng th scale of genetic hypotheses that are addressable by those data. No 'simp le' formula exists when image resolution is sufficient to test a given geom orphic process, which is dependent on what characteristics are diagnostic o f the particular process. Genetic hypotheses should be formulated along the lines of the "multiple working hypotheses" concept as described in a class ic paper by Chamberlin [J, Geol, 5 (1897) 837]. An essential element of a v iable working hypothesis is a clear indication of the characteristics predi cted by, or a consequence of, the hypothesis. An untestable hypothesis is n ot an effective working hypothesis. The history of the study of lunar sinuo us rilles is outlined as an illustration of the influence of image resoluti on and the formulation of genetic hypotheses on the subsequent advancement of understanding of the problem. Sinuous rilles on Venus and Mars, and cont roversial sinuous ridges on Mars are also reviewed. In the lunar case, the three-order-of-magnitude improvement in spatial resolution provided by Luna r Orbiter photographs over Earth-based telescopic photographs did nor resul t in definitive examination and elimination of published hypotheses for the formation of sinuous rilles. Topographic data obtained from cartographical ly controlled Apollo orbital photographs, along with important observations and samples obtained by the astronauts on the lunar surface, did test and exclude several hypotheses. The formulation of a genetic hypothesis, includ ing testable consequences of that hypothesis, is a greater determinant of i ts ultimate utility to the scientific community than is the image resolutio n available at any,given time. Published by Elsevier Science B.V.