Comparison of knobs on mars to isolated hills in eolian, fluvial and glacial environments

Abstract

Positive isolated features or knobs have been observed on Mars since Mariner 9 first photographed the planet in 1972. More recently, the Viking Orbiters photographed the surface at increased resolution. With the use of Viking photomosaics, a systematic search for knobs was completed. The knobs were characterized by length, width, geographic location, proximity to streaks and geologic surroundings. Similar isolated features on Earth eroded by fluvial, glacial, and eolian processes were studied and measured. Comparison of length-to-width ratios of Martian knobs to isolated hills on Earth indicate that the Martian knobs are most similar to the isolated hills formed in a hyper-arid environment. The terrestrial features were probably formed initially when solid rock was fractured, then wind erosion, starting at the fractures, continued to sweep away sediments leaving isolated hills. Such hills in fluvial and glacial environments have length-to-width ratios significantly higher than those of the Martian knobs. Other diagnostic features associated with such environments are absent in the case of the Martian knobs. Moreover, streaks, splotches, dunes and pitted and fluted rocks, all indicative of a eolian regime, are associated with the Martian knobs.